2009-03-20T08:15:42Z

John Rula: /* Distance Calculation */

[[Image:Mechatronics2009Bball|right|thumb|180px]]
<br=clear all>
== Team Members ==
[[image:Team_12_Mechatronics_2009|Team Members from right to left: John, Alex, and Meredith|thumb|250px|right]]
* John Rula (Mechanical Engineering, Class of 2009)
* Alex Wojcicki (Mechanical Engineering, Class of 2009)
* Meredith Chow (Electrical Engineering, Class of 2010)

 

== Introduction ==

A throwing arm propelled by a Pittman DC brush motor is mounted on a turntable and throws the ball into the "hoop." The hoop is wrapped in reflective tape and an IR emitter, receiver pair is used to sense where the IR is reflected most (the hoop with highly reflective tape). An ultrasonic sensor then pings the hoop for the distance of the hoop. With this information, the arm is able to "make a basket."
[[Image:Mechatronics2009Bball|Entire system|left|thumb|200px]][[Image:mech2009bballcloseup|Front view|left|thumb|200px]][[Image:mech2009bballcloseupalternate|Close up|left|thumb|350px]]
 

== Mechanical Design ==
[[Image:Mechatronics2009BballCADassembly|CAD assembly|right|thumb|250px]]
The major mechanical components were machined out of clear acrylic using the laser cutter in the machine shop. Holes were machined and threaded as required. The base is a square (12" x 12") with threaded holes for attachment to the purchased turntable bearing. The turntable has threaded holes for attachment to the turntable bearing as well. Large holes were added to the turntable for screw access during assembly because once one of the parts is attached to the turntable, the screws would otherwise not be able to be tightened. The turntable features a rectangular cutout for the servo motor and threaded holes for mounting. There are additional through holes for mounting the sensor bracket and the motor supports.

Two motor supports were designed to accept the Pittman motor and hold it six inches above the turntable surface. Fasteners are inserted from below the turntable into threaded holes in the motor supports. Clamps were designed to thread onto the supports and secure the motor in place. The sensors (IR emitter/receiver pair and ultrasonic sensor) are mounted on a machined acrylic bracket that which is attached to the turntable again through fasteners inserted underneath the turntable.

The arm is also made of laser cut acrylic. It was designed with a close fit on the flat of the motor shaft and with a clamp for tightening using a threaded fastener. For manufacturing reasons, the ball holding portion of the arm was cut out of a separate piece of acrylic and secured to the end of the throwing arm.

The hoop can be anything with the highly reflective tape around it. It is suggested to have a circular profile for better performance detecting its center using the IR emitter/receiver.
[[Image:Mechatronics2009BballArmCloseup|Throwing arm attachment close up|right|thumb|250px]]

=== Mechanical Components ===

<table border=1>
<tr><th>Part</th><th>Part No.</th><th>Qty</th><th>Vendor</th><th>Price (Total)</th></tr>
<tr><td>Pittman Motor </td><td>GM8712</td><td>1</td><td>Lab</td><td>-</td></tr>
<tr><td>RC Servo Motor - Futaba </td><td>S3004</td><td>1</td><td>Lab</td><td>-</td></tr>
<tr><td>Acrylic .25" Thick, 24"X 24"</td><td>8560K357</td><td>1</td><td>[http://www.mcmaster.com/#8560K357 McMaster]</td><td>$39.63</td></tr>
<tr><td>Corrosion-Resistant Turntable</td><td>6031K17</td><td>1</td><td>[http://www.mcmaster.com/#6031k17 McMaster]</td><td>$2.42</td></tr>
<tr><td>Fasteners</td><td>-</td><td>24</td><td>Shop supply</td><td>-</td></tr>
<tr><td>Rubber Feet</td><td>-</td><td>4</td><td>Lab</td><td>-</td></tr>
</table>
 

== Electrical Design ==
The IR pair, ultrasonic, and servo have a relatively simple circuit. In the diagram below, the IR pair, ultrasonic, and servo are controlled by the program on PIC1. The IR pair and ultrasonic sensor are stacked vertically and inserted into the fitted holes on the laser cut acrylic. Because of the close proximity of the IR pair, to prevent saturation of the IR receiver, the emitter was wrapped in electrical tape. This allowed for the detection of reflected IR rather than from the emitter right below the detector. The RC servo goes through a sweep looking for the hoop. It finds the hoop by storing the location of the highest IR detection. The reflective tape used in Design Challenge 2008 and 2009 was used to wrap the hoop and is used to assist in the finding of the hoop as it reflects more IR radiation than most common objects. After making its sweep, the servo returns to the position where the most IR was detected. The ultrasonic sensor will then ping the hoop to find the distance of the hoop.

The Pittman motor, H-Bridge, and encoder chip circuit is more complex. This circuit is run by PIC2. The information collected about the hoop location is communicated from PIC1 to PIC2. The Pittman is used to launch the ball. After the hoop is found, the arm attached to the Pittman launches the ball into the hoop. The shaft rotates forward and then reverses to its previous position. The device is then ready to find the hoop and launch the ball again.

The two PICs communicated with a common ground and wire connecting RC6 and RC7 as shown in the diagram. The power supply was two 12 volt power supplies connected in series to give a total of 24 volts.

=== Electrical Components ===
<table border=1>
<tr><th>Part</th><th>Part No.</th><th>Qty</th><th>Vendor</th><th>Price (Total)</th></tr>
<tr><td>PICs</td><td>PIC18F4520</td><td>2</td><td>Lab</td><td>-</td></tr>
<tr><td>Encoder</td><td>LS7083</td><td>1</td><td>Lab</td><td>-</td></tr>
<tr><td>H-Bridge</td><td>L298N</td><td>1</td><td>Lab</td><td>-</td></tr>
<tr><td>Ping Ultrasonic Sensor</td><td>28015</td><td>1</td><td>Lab 5 supply</td><td>-</td></tr>
<tr><td>IR Emitter</td><td>QED123</td><td>1</td><td>Lab</td><td>-</td></tr>
<tr><td>IR Phototransistor</td><td>LTR-4206E</td><td>1</td><td>Lab</td><td>-</td></tr>
<tr><td>Diodes</td><td>1N4148</td><td>4</td><td>Lab</td><td>-</td></tr>
<tr><td>Resistors</td><td>47.5/150K</td><td>2</td><td>Lab</td><td>-</td></tr>
</table>
 

=== Circuit Diagram ===
[[image:team12mech2009cktwiki|Circuit diagram of how the the pics, sensors, and motor components are connected.|thumb|500px|left]][[image:mech2009bballelectronics|How the the pics, sensors, and motor components are connected.|thumb|500px|left]]

 

== Code ==

We used two PICs for this project. One ran the motor control since we wanted the smallest interrupt possible for the most accurate speed control. The other PIC ran the servo attached to the turntable as well as the infrared and ultrasonic sensors.

The motor was controlled using a PD controller which controlled both speed and position. Theory behind the controller was that if accurate speed control could be achieved along with the ability to control the release point by stopping the motor, we could control the distance the ball traveled to a high degree of accuracy having it follow simple kinematic equations. The launch was triggered when the ultrasonic sensor distance was sent to it. We opted against I2C and instead went with RS-232 for simplicity since we were only sending two bytes of data.

Full source code of the motor controller can be found [[Media:Motor-Control.c|here]].

== PD Controller ==

#INT_TIMER2 // designates that this is the routine to call when timer3 overflows
void Timer2isr() {
milsecs++;
if ((milsecs & 7) == 0) { // servo routine every 4ms is plenty. 250x/sec
//update counters and encoder
upCount = get_timer0();
encoderActual += upCount - lastUpCount;
downCount = get_timer1();
encoderActual -= downCount - lastDownCount;
lastUpCount = upCount;
lastDownCount = downCount;
We used hardware encoders due to the speed of rotation of the shaft.
theta = (int16)(encoderActual - offset) % EncCount;
thetaError = (signed int32)thetaTarget- (signed int32)theta;
Theta was used for position control. Due to the way we implemented it, the motor was only was only allowed 359.9 degrees of rotation which was suitable for our launching arm.
//speed controls whether it is in forward or reverse
if(thetaError > 0) speed = targetSpeed;
else if(thetaError < 0) speed = -targetSpeed;
A positive thetaError indicated that the motor needed to move CCW to reach its destination A negative thetaError indicated that the motor needed to move CW to reach its destination.
encoderTarget += speed; //need to add accuracy to speed
encoderTargetTheta = (int16)(encoderTarget) % EncCount;

if(encoderTargetTheta > thetaTarget && speed > 0) {
encoderTarget -= encoderTargetTheta - thetaTarget;
targetSpeed = 0;
} else if(encoderTargetTheta < thetaTarget && speed < 0) {
encoderTarget += thetaTarget - encoderTargetTheta;
targetSpeed = 0;
}
The encoderTargetTheta was used to handle the case of overshoots and was the theta value of the encoderTarget after the speed was added. If that theta value was above/below (depending on direction) the target theta value, it represented that the input had reached its destination, so the speed drops to zero, and the encoderTarget is set to the correct target value.
//do calculations for PD controller with new error
error = encoderTarget - (encoderActual - initialCount);
derivative = error - lastError;
lastError = error;

//At different speeds, need different gains, higher kps and kds for higher speeds ect...
if(speed <= 5) {
Torque = 3*error + 2*derivative;
} else
if (speed <= 75) {
Torque = 1.25 * error + 3 * derivative;
} else if (speed <= 100) {
Torque = 2 * error + 6 * derivative;
} else { //speed > 100
Torque = pGain * error + dGain * derivative;
}
In tuning the PD controller, it was found that different speeds needed different tunings in order to receive a smooth and accurate response. These values represent the best values we were able to obtain in tuning.
if(error > 0) { //going in the CCW direction, Torque positive
output_low(PIN_C4);
}
else if(error < 0) {
//invert for PWM
Torque = 624 + Torque;
output_high(PIN_C4);
if(launching == 1 && thetaError < 0) { //used to tune when launching
launching = 0;
thetaTarget = 300;
targetSpeed = 10;
}
}
Set PWM values to make motor go forward or reverse. Also, the case where 'launching==1' is to return the arm to a loading position after the arm has shot a ball.
if(Torque < 0) Torque = 0;
if(Torque > 624) Torque = 624;
set_pwm1_duty(Torque);

}
}
Set the motor's PWM and check for maximum and minimum values. 624 was used instead of 78 for PWM values based on how we set up our timer2.

== PIC to PIC communication with RS-232 ==
We choose to use RS-232 to communicate between PICs because of the small amount of data we were sending (a single int16) and to avoid the overhead required by I2C. We accomplished this by breaking our values into 8-bit chunks cast as chars and sending them one at a time.

sendDistance = avgdistance*100; //distance in cm\

//Break distance into two 8-bit ints and cast as chars to send over RS-232
//Will be reassembled on other pic
putc((char)(sendDistance>>8));
putc((char)(sendDistance & 255));
Code to send value.

#INT_RDA
void INTRDAisr() {

if(kbhit()) {
if(rsCount == 0) c_0 = getc();
else if(rsCount == 1) {
c_1 = getc();
distance = (int16)c_1 + ((int16)c_0<<8);
CalculateAndLaunch((float)distance);
}
}

rsCount++;
if(rsCount >= 2) rsCount = 0;
}
This interrupt is called when the hardware RS-232 receives a byte of data. Once two bytes of data are received (int16), the interrupt reassembles them into a single int16 and calls CalculateAndLaunch().

void main() {

setup_timer_2(T2_DIV_BY_4, 78, 16);
setup_timer_0(RTCC_EXT_L_TO_H | RTCC_DIV_1); //Counter used for Encoder A -- Up Count
setup_timer_1(T1_EXTERNAL | T1_DIV_BY_1); //Counter used for Encoder B -- Down Count

//setup offsets and intialize encoders
upCount = get_timer0();
downCount = get_timer1();
lastUpCount = upCount;
lastDownCount = downCount;

encoderActual += (upCount - downCount);

initialCount = encoderActual;

offset = encoderActual%EncCount;
if(encoderActual < 0) offset = -offset;

enable_interrupts(INT_TIMER2);
enable_interrupts(INT_RDA);
enable_interrupts(GLOBAL);
ext_int_edge(0, H_TO_L); // interrupt on INT0/RB0 pin, low to high transition
setup_ccp1(CCP_PWM);

set_pwm1_duty(0);
output_low(PIN_C4);
delay_us(10);

while(TRUE) {
delay_ms(5000);
}
}
== Distance Calculation ==
Shot distance was based on a second order polynomial fit we obtained experimentally. The data we collected is shown in the image on the right. [[Image:Distance-Calibration-basketball.png | Calibration data and trendline | thumb | 300px | right]]
void LaunchBall(int16 speed, int16 angle) {
targetSpeed = speed;
thetaTarget = angle;
launching=1;
}

void CalculateAndLaunch(float dist) {
dist = dist+30; //adjust for distance between ranger and motor
shotSpeed = -0.0012*(dist*dist) + 0.5884*dist + 89.678;
LaunchBall((int16)(shotSpeed/2), 3000);
}

== Results ==
In the end, the project ultimately succeeded -- baskets could be made. However, better tuning for the motor control and needs to be developed for more consistent results.

[http://www.youtube.com/watch?v=Y466dzP-qiY Link To Video]

===Problems Encountered===

*Attempting to integrate multiple pics and circuits onto one circuit board did not give good results. Ultimately, we had to use separate boards for each pic. This could be due to the effect of motor noise on our control circuitry.

*Motor control was an intense programming effort -- almost a project in its own right. Trying to combine the motor control and calibrate our throwing distance was difficult. Designing a functioning throwing device along with getting the rest of the project implemented was difficult to complete with the given time constraints.

*Many components burned out. Fly back diodes were implemented however, we still went through quite a few H-bridges. Encoder chips also burned out. The PING sensor burned out as well. We are not sure of the cause of some of these part failures.

*The length of wires for the Encoder A and B should be limited. When using long wires running from the encoder, we were not able to get our encoder chip to function properly. Replacing them with shorter wires fixed the issue. Because the signal from the encoder is switching at such high speeds, the loss in the long wires played a significant effect resulting in a faulty encoder count. Larger diameter wires may be an alternate solution to this problem.

== Notes ==
A few things we might change if we did it again:
*Simplify the motor control portion of the project. Trying to implement a speed control using the encoder count was difficult to implement. Simply using PWM to drive the motor at different speeds may have been sufficient.
*Test different wires for length and diameter for optimal performance for the Encoder A and B connections.
*Combine the PICs on one circuit board, solving the issues we encountered when attempting this.
*Perform a more detailed calibration, adjusting starting position, final launching position, and speed to get improved control over throwing distance.

Basketball

2009-03-20T08:14:26Z

John Rula: /* PD Controller */

[[Image:Mechatronics2009Bball|right|thumb|180px]]
<br=clear all>
== Team Members ==
[[image:Team_12_Mechatronics_2009|Team Members from right to left: John, Alex, and Meredith|thumb|250px|right]]
* John Rula (Mechanical Engineering, Class of 2009)
* Alex Wojcicki (Mechanical Engineering, Class of 2009)
* Meredith Chow (Electrical Engineering, Class of 2010)

 

== Introduction ==

A throwing arm propelled by a Pittman DC brush motor is mounted on a turntable and throws the ball into the "hoop." The hoop is wrapped in reflective tape and an IR emitter, receiver pair is used to sense where the IR is reflected most (the hoop with highly reflective tape). An ultrasonic sensor then pings the hoop for the distance of the hoop. With this information, the arm is able to "make a basket."
[[Image:Mechatronics2009Bball|Entire system|left|thumb|200px]][[Image:mech2009bballcloseup|Front view|left|thumb|200px]][[Image:mech2009bballcloseupalternate|Close up|left|thumb|350px]]
 

== Mechanical Design ==
[[Image:Mechatronics2009BballCADassembly|CAD assembly|right|thumb|250px]]
The major mechanical components were machined out of clear acrylic using the laser cutter in the machine shop. Holes were machined and threaded as required. The base is a square (12" x 12") with threaded holes for attachment to the purchased turntable bearing. The turntable has threaded holes for attachment to the turntable bearing as well. Large holes were added to the turntable for screw access during assembly because once one of the parts is attached to the turntable, the screws would otherwise not be able to be tightened. The turntable features a rectangular cutout for the servo motor and threaded holes for mounting. There are additional through holes for mounting the sensor bracket and the motor supports.

Two motor supports were designed to accept the Pittman motor and hold it six inches above the turntable surface. Fasteners are inserted from below the turntable into threaded holes in the motor supports. Clamps were designed to thread onto the supports and secure the motor in place. The sensors (IR emitter/receiver pair and ultrasonic sensor) are mounted on a machined acrylic bracket that which is attached to the turntable again through fasteners inserted underneath the turntable.

The arm is also made of laser cut acrylic. It was designed with a close fit on the flat of the motor shaft and with a clamp for tightening using a threaded fastener. For manufacturing reasons, the ball holding portion of the arm was cut out of a separate piece of acrylic and secured to the end of the throwing arm.

The hoop can be anything with the highly reflective tape around it. It is suggested to have a circular profile for better performance detecting its center using the IR emitter/receiver.
[[Image:Mechatronics2009BballArmCloseup|Throwing arm attachment close up|right|thumb|250px]]

=== Mechanical Components ===

<table border=1>
<tr><th>Part</th><th>Part No.</th><th>Qty</th><th>Vendor</th><th>Price (Total)</th></tr>
<tr><td>Pittman Motor </td><td>GM8712</td><td>1</td><td>Lab</td><td>-</td></tr>
<tr><td>RC Servo Motor - Futaba </td><td>S3004</td><td>1</td><td>Lab</td><td>-</td></tr>
<tr><td>Acrylic .25" Thick, 24"X 24"</td><td>8560K357</td><td>1</td><td>[http://www.mcmaster.com/#8560K357 McMaster]</td><td>$39.63</td></tr>
<tr><td>Corrosion-Resistant Turntable</td><td>6031K17</td><td>1</td><td>[http://www.mcmaster.com/#6031k17 McMaster]</td><td>$2.42</td></tr>
<tr><td>Fasteners</td><td>-</td><td>24</td><td>Shop supply</td><td>-</td></tr>
<tr><td>Rubber Feet</td><td>-</td><td>4</td><td>Lab</td><td>-</td></tr>
</table>
 

== Electrical Design ==
The IR pair, ultrasonic, and servo have a relatively simple circuit. In the diagram below, the IR pair, ultrasonic, and servo are controlled by the program on PIC1. The IR pair and ultrasonic sensor are stacked vertically and inserted into the fitted holes on the laser cut acrylic. Because of the close proximity of the IR pair, to prevent saturation of the IR receiver, the emitter was wrapped in electrical tape. This allowed for the detection of reflected IR rather than from the emitter right below the detector. The RC servo goes through a sweep looking for the hoop. It finds the hoop by storing the location of the highest IR detection. The reflective tape used in Design Challenge 2008 and 2009 was used to wrap the hoop and is used to assist in the finding of the hoop as it reflects more IR radiation than most common objects. After making its sweep, the servo returns to the position where the most IR was detected. The ultrasonic sensor will then ping the hoop to find the distance of the hoop.

The Pittman motor, H-Bridge, and encoder chip circuit is more complex. This circuit is run by PIC2. The information collected about the hoop location is communicated from PIC1 to PIC2. The Pittman is used to launch the ball. After the hoop is found, the arm attached to the Pittman launches the ball into the hoop. The shaft rotates forward and then reverses to its previous position. The device is then ready to find the hoop and launch the ball again.

The two PICs communicated with a common ground and wire connecting RC6 and RC7 as shown in the diagram. The power supply was two 12 volt power supplies connected in series to give a total of 24 volts.

=== Electrical Components ===
<table border=1>
<tr><th>Part</th><th>Part No.</th><th>Qty</th><th>Vendor</th><th>Price (Total)</th></tr>
<tr><td>PICs</td><td>PIC18F4520</td><td>2</td><td>Lab</td><td>-</td></tr>
<tr><td>Encoder</td><td>LS7083</td><td>1</td><td>Lab</td><td>-</td></tr>
<tr><td>H-Bridge</td><td>L298N</td><td>1</td><td>Lab</td><td>-</td></tr>
<tr><td>Ping Ultrasonic Sensor</td><td>28015</td><td>1</td><td>Lab 5 supply</td><td>-</td></tr>
<tr><td>IR Emitter</td><td>QED123</td><td>1</td><td>Lab</td><td>-</td></tr>
<tr><td>IR Phototransistor</td><td>LTR-4206E</td><td>1</td><td>Lab</td><td>-</td></tr>
<tr><td>Diodes</td><td>1N4148</td><td>4</td><td>Lab</td><td>-</td></tr>
<tr><td>Resistors</td><td>47.5/150K</td><td>2</td><td>Lab</td><td>-</td></tr>
</table>
 

=== Circuit Diagram ===
[[image:team12mech2009cktwiki|Circuit diagram of how the the pics, sensors, and motor components are connected.|thumb|500px|left]][[image:mech2009bballelectronics|How the the pics, sensors, and motor components are connected.|thumb|500px|left]]

 

== Code ==

We used two PICs for this project. One ran the motor control since we wanted the smallest interrupt possible for the most accurate speed control. The other PIC ran the servo attached to the turntable as well as the infrared and ultrasonic sensors.

The motor was controlled using a PD controller which controlled both speed and position. Theory behind the controller was that if accurate speed control could be achieved along with the ability to control the release point by stopping the motor, we could control the distance the ball traveled to a high degree of accuracy having it follow simple kinematic equations. The launch was triggered when the ultrasonic sensor distance was sent to it. We opted against I2C and instead went with RS-232 for simplicity since we were only sending two bytes of data.

Full source code of the motor controller can be found [[Media:Motor-Control.c|here]].

== PD Controller ==

#INT_TIMER2 // designates that this is the routine to call when timer3 overflows
void Timer2isr() {
milsecs++;
if ((milsecs & 7) == 0) { // servo routine every 4ms is plenty. 250x/sec
//update counters and encoder
upCount = get_timer0();
encoderActual += upCount - lastUpCount;
downCount = get_timer1();
encoderActual -= downCount - lastDownCount;
lastUpCount = upCount;
lastDownCount = downCount;
We used hardware encoders due to the speed of rotation of the shaft.
theta = (int16)(encoderActual - offset) % EncCount;
thetaError = (signed int32)thetaTarget- (signed int32)theta;
Theta was used for position control. Due to the way we implemented it, the motor was only was only allowed 359.9 degrees of rotation which was suitable for our launching arm.
//speed controls whether it is in forward or reverse
if(thetaError > 0) speed = targetSpeed;
else if(thetaError < 0) speed = -targetSpeed;
A positive thetaError indicated that the motor needed to move CCW to reach its destination A negative thetaError indicated that the motor needed to move CW to reach its destination.
encoderTarget += speed; //need to add accuracy to speed
encoderTargetTheta = (int16)(encoderTarget) % EncCount;

if(encoderTargetTheta > thetaTarget && speed > 0) {
encoderTarget -= encoderTargetTheta - thetaTarget;
targetSpeed = 0;
} else if(encoderTargetTheta < thetaTarget && speed < 0) {
encoderTarget += thetaTarget - encoderTargetTheta;
targetSpeed = 0;
}
The encoderTargetTheta was used to handle the case of overshoots and was the theta value of the encoderTarget after the speed was added. If that theta value was above/below (depending on direction) the target theta value, it represented that the input had reached its destination, so the speed drops to zero, and the encoderTarget is set to the correct target value.
//do calculations for PD controller with new error
error = encoderTarget - (encoderActual - initialCount);
derivative = error - lastError;
lastError = error;

//At different speeds, need different gains, higher kps and kds for higher speeds ect...
if(speed <= 5) {
Torque = 3*error + 2*derivative;
} else
if (speed <= 75) {
Torque = 1.25 * error + 3 * derivative;
} else if (speed <= 100) {
Torque = 2 * error + 6 * derivative;
} else { //speed > 100
Torque = pGain * error + dGain * derivative;
}
In tuning the PD controller, it was found that different speeds needed different tunings in order to receive a smooth and accurate response. These values represent the best values we were able to obtain in tuning.
if(error > 0) { //going in the CCW direction, Torque positive
output_low(PIN_C4);
}
else if(error < 0) {
//invert for PWM
Torque = 624 + Torque;
output_high(PIN_C4);
if(launching == 1 && thetaError < 0) { //used to tune when launching
launching = 0;
thetaTarget = 300;
targetSpeed = 10;
}
}
Set PWM values to make motor go forward or reverse. Also, the case where 'launching==1' is to return the arm to a loading position after the arm has shot a ball.
if(Torque < 0) Torque = 0;
if(Torque > 624) Torque = 624;
set_pwm1_duty(Torque);

}
}
Set the motor's PWM and check for maximum and minimum values. 624 was used instead of 78 for PWM values based on how we set up our timer2.

== PIC to PIC communication with RS-232 ==
We choose to use RS-232 to communicate between PICs because of the small amount of data we were sending (a single int16) and to avoid the overhead required by I2C. We accomplished this by breaking our values into 8-bit chunks cast as chars and sending them one at a time.

sendDistance = avgdistance*100; //distance in cm\

//Break distance into two 8-bit ints and cast as chars to send over RS-232
//Will be reassembled on other pic
putc((char)(sendDistance>>8));
putc((char)(sendDistance & 255));
Code to send value.

#INT_RDA
void INTRDAisr() {

if(kbhit()) {
if(rsCount == 0) c_0 = getc();
else if(rsCount == 1) {
c_1 = getc();
distance = (int16)c_1 + ((int16)c_0<<8);
CalculateAndLaunch((float)distance);
}
}

rsCount++;
if(rsCount >= 2) rsCount = 0;
}
This interrupt is called when the hardware RS-232 receives a byte of data. Once two bytes of data are received (int16), the interrupt reassembles them into a single int16 and calls CalculateAndLaunch().

void main() {

setup_timer_2(T2_DIV_BY_4, 78, 16);
setup_timer_0(RTCC_EXT_L_TO_H | RTCC_DIV_1); //Counter used for Encoder A -- Up Count
setup_timer_1(T1_EXTERNAL | T1_DIV_BY_1); //Counter used for Encoder B -- Down Count

//setup offsets and intialize encoders
upCount = get_timer0();
downCount = get_timer1();
lastUpCount = upCount;
lastDownCount = downCount;

encoderActual += (upCount - downCount);

initialCount = encoderActual;

offset = encoderActual%EncCount;
if(encoderActual < 0) offset = -offset;

enable_interrupts(INT_TIMER2);
enable_interrupts(INT_RDA);
enable_interrupts(GLOBAL);
ext_int_edge(0, H_TO_L); // interrupt on INT0/RB0 pin, low to high transition
setup_ccp1(CCP_PWM);

set_pwm1_duty(0);
output_low(PIN_C4);
delay_us(10);

while(TRUE) {
delay_ms(5000);
}
}
== Distance Calculation ==
Shot distance was based on a second order polynomial fit we obtained experimentally. The data we collected is shown in the image on the right. [[Image:Distance-Calibration-basketball.png]]
void LaunchBall(int16 speed, int16 angle) {
targetSpeed = speed;
thetaTarget = angle;
launching=1;
}

void CalculateAndLaunch(float dist) {
dist = dist+30; //adjust for distance between ranger and motor
shotSpeed = -0.0012*(dist*dist) + 0.5884*dist + 89.678;
LaunchBall((int16)(shotSpeed/2), 3000);
}

== Results ==
In the end, the project ultimately succeeded -- baskets could be made. However, better tuning for the motor control and needs to be developed for more consistent results.

[http://www.youtube.com/watch?v=Y466dzP-qiY Link To Video]

===Problems Encountered===

*Attempting to integrate multiple pics and circuits onto one circuit board did not give good results. Ultimately, we had to use separate boards for each pic. This could be due to the effect of motor noise on our control circuitry.

*Motor control was an intense programming effort -- almost a project in its own right. Trying to combine the motor control and calibrate our throwing distance was difficult. Designing a functioning throwing device along with getting the rest of the project implemented was difficult to complete with the given time constraints.

*Many components burned out. Fly back diodes were implemented however, we still went through quite a few H-bridges. Encoder chips also burned out. The PING sensor burned out as well. We are not sure of the cause of some of these part failures.

*The length of wires for the Encoder A and B should be limited. When using long wires running from the encoder, we were not able to get our encoder chip to function properly. Replacing them with shorter wires fixed the issue. Because the signal from the encoder is switching at such high speeds, the loss in the long wires played a significant effect resulting in a faulty encoder count. Larger diameter wires may be an alternate solution to this problem.

== Notes ==
A few things we might change if we did it again:
*Simplify the motor control portion of the project. Trying to implement a speed control using the encoder count was difficult to implement. Simply using PWM to drive the motor at different speeds may have been sufficient.
*Test different wires for length and diameter for optimal performance for the Encoder A and B connections.
*Combine the PICs on one circuit board, solving the issues we encountered when attempting this.
*Perform a more detailed calibration, adjusting starting position, final launching position, and speed to get improved control over throwing distance.

Basketball

2009-03-20T07:31:22Z

John Rula: /* Results */

[[Image:Mechatronics2009Bball|right|thumb|180px]]
<br=clear all>
== Team Members ==
[[image:Team_12_Mechatronics_2009|Team Members from right to left: John, Alex, and Meredith|thumb|250px|right]]
* John Rula (Mechanical Engineering, Class of 2009)
* Alex Wojcicki (Mechanical Engineering, Class of 2009)
* Meredith Chow (Electrical Engineering, Class of 2010)

 

== Introduction ==

A throwing arm propelled by a Pittman DC brush motor is mounted on a turntable and throws the ball into the "hoop." The hoop is wrapped in reflective tape and an IR emitter, receiver pair is used to sense where the IR is reflected most (the hoop with highly reflective tape). An ultrasonic sensor then pings the hoop for the distance of the hoop. With this information, the arm is able to "make a basket."
[[Image:Mechatronics2009Bball|Entire system|left|thumb|200px]][[Image:mech2009bballcloseup|Front view|left|thumb|200px]][[Image:mech2009bballcloseupalternate|Close up|left|thumb|350px]]
 

== Mechanical Design ==
[[Image:Mechatronics2009BballCADassembly|CAD assembly|right|thumb|250px]]
The major mechanical components were machined out of clear acrylic using the laser cutter in the machine shop. Holes were machined and threaded as required. The base is a square (12" x 12") with threaded holes for attachment to the purchased turntable bearing. The turntable has threaded holes for attachment to the turntable bearing as well. Large holes were added to the turntable for screw access during assembly because once one of the parts is attached to the turntable, the screws would otherwise not be able to be tightened. The turntable features a rectangular cutout for the servo motor and threaded holes for mounting. There are additional through holes for mounting the sensor bracket and the motor supports.

Two motor supports were designed to accept the Pittman motor and hold it six inches above the turntable surface. Fasteners are inserted from below the turntable into threaded holes in the motor supports. Clamps were designed to thread onto the supports and secure the motor in place. The sensors (IR emitter/receiver pair and ultrasonic sensor) are mounted on a machined acrylic bracket that which is attached to the turntable again through fasteners inserted underneath the turntable.

The arm is also made of laser cut acrylic. It was designed with a close fit on the flat of the motor shaft and with a clamp for tightening using a threaded fastener. For manufacturing reasons, the ball holding portion of the arm was cut out of a separate piece of acrylic and secured to the end of the throwing arm.

The hoop can be anything with the highly reflective tape around it. It is suggested to have a circular profile for better performance detecting its center using the IR emitter/receiver.
[[Image:Mechatronics2009BballArmCloseup|Throwing arm attachment close up|right|thumb|250px]]

=== Mechanical Components ===

<table border=1>
<tr><th>Part</th><th>Part No.</th><th>Qty</th><th>Vendor</th><th>Price (Total)</th></tr>
<tr><td>Pittman Motor </td><td>GM8712</td><td>1</td><td>Lab</td><td>-</td></tr>
<tr><td>RC Servo Motor - Futaba </td><td>S3004</td><td>1</td><td>Lab</td><td>-</td></tr>
<tr><td>Acrylic .25" Thick, 24"X 24"</td><td>8560K357</td><td>1</td><td>[http://www.mcmaster.com/#8560K357 McMaster]</td><td>$39.63</td></tr>
<tr><td>Corrosion-Resistant Turntable</td><td>6031K17</td><td>1</td><td>[http://www.mcmaster.com/#6031k17 McMaster]</td><td>$2.42</td></tr>
<tr><td>Fasteners</td><td>-</td><td>24</td><td>Shop supply</td><td>-</td></tr>
<tr><td>Rubber Feet</td><td>-</td><td>4</td><td>Lab</td><td>-</td></tr>
</table>
 

== Electrical Design ==
The IR pair, ultrasonic, and servo have a relatively simple circuit. In the diagram below, the IR pair, ultrasonic, and servo are controlled by the program on PIC1. The IR pair and ultrasonic sensor are stacked vertically and inserted into the fitted holes on the laser cut acrylic. Because of the close proximity of the IR pair, to prevent saturation of the IR receiver, the emitter was wrapped in electrical tape. This allowed for the detection of reflected IR rather than from the emitter right below the detector. The RC servo goes through a sweep looking for the hoop. It finds the hoop by storing the location of the highest IR detection. The reflective tape used in Design Challenge 2008 and 2009 was used to wrap the hoop and is used to assist in the finding of the hoop as it reflects more IR radiation than most common objects. After making its sweep, the servo returns to the position where the most IR was detected. The ultrasonic sensor will then ping the hoop to find the distance of the hoop.

The Pittman motor, H-Bridge, and encoder chip circuit is more complex. This circuit is run by PIC2. The information collected about the hoop location is communicated from PIC1 to PIC2. The Pittman is used to launch the ball. After the hoop is found, the arm attached to the Pittman launches the ball into the hoop. The shaft rotates forward and then reverses to its previous position. The device is then ready to find the hoop and launch the ball again.

The two PICs communicated with a common ground and wire connecting RC6 and RC7 as shown in the diagram. The power supply was two 12 volt power supplies connected in series to give a total of 24 volts.

=== Electrical Components ===
<table border=1>
<tr><th>Part</th><th>Part No.</th><th>Qty</th><th>Vendor</th><th>Price (Total)</th></tr>
<tr><td>PICs</td><td>PIC18F4520</td><td>2</td><td>Lab</td><td>-</td></tr>
<tr><td>Encoder</td><td>LS7083</td><td>1</td><td>Lab</td><td>-</td></tr>
<tr><td>H-Bridge</td><td>L298N</td><td>1</td><td>Lab</td><td>-</td></tr>
<tr><td>Ping Ultrasonic Sensor</td><td>28015</td><td>1</td><td>Lab 5 supply</td><td>-</td></tr>
<tr><td>IR Emitter</td><td>QED123</td><td>1</td><td>Lab</td><td>-</td></tr>
<tr><td>IR Phototransistor</td><td>LTR-4206E</td><td>1</td><td>Lab</td><td>-</td></tr>
<tr><td>Diodes</td><td>1N4148</td><td>4</td><td>Lab</td><td>-</td></tr>
<tr><td>Resistors</td><td>47.5/150K</td><td>2</td><td>Lab</td><td>-</td></tr>
</table>
 

=== Circuit Diagram ===
[[image:team12mech2009cktwiki|Circuit diagram of how the the pics, sensors, and motor components are connected.|thumb|500px|left]][[image:mech2009bballelectronics|How the the pics, sensors, and motor components are connected.|thumb|500px|left]]

 

== Code ==

We used two PICs for this project. One ran the motor control since we wanted the smallest interrupt possible for the most accurate speed control. The other PIC ran the servo attached to the turntable as well as the infrared and ultrasonic sensors.

The motor was controlled using a PD controller which controlled both speed and position. Theory behind the controller was that if accurate speed control could be achieved along with the ability to control the release point by stopping the motor, we could control the distance the ball traveled to a high degree of accuracy having it follow simple kinematic equations. The launch was triggered when the ultrasonic sensor distance was sent to it. We opted against I2C and instead went with RS-232 for simplicity since we were only sending two bytes of data.

Full source code of the motor controller can be found [[Media:Motor-Control.c|here]].

== PD Controller ==

#INT_TIMER2 // designates that this is the routine to call when timer3 overflows
void Timer2isr() {
milsecs++;
if ((milsecs & 7) == 0) { // servo routine every 4ms is plenty. 250x/sec
//update counters and encoder
upCount = get_timer0();
encoderActual += upCount - lastUpCount; //NEW HERE (REMOVED (SIGNED INT16 CAST)
downCount = get_timer1();
encoderActual -= downCount - lastDownCount; //NEW HERE SAME AS ABOVE
lastUpCount = upCount;
lastDownCount = downCount;

theta = (int16)(encoderActual - offset) % EncCount;
thetaError = (signed int32)thetaTarget- (signed int32)theta;

//speed controls whether it is in forward or reverse
if(thetaError > 0) speed = targetSpeed;
else if(thetaError < 0) speed = -targetSpeed;

encoderTarget += speed; //need to add accuracy to speed
encoderTargetTheta = (int16)(encoderTarget) % EncCount;

if(encoderTargetTheta > thetaTarget && speed > 0) {
encoderTarget -= encoderTargetTheta - thetaTarget;
targetSpeed = 0;
} else if(encoderTargetTheta < thetaTarget && speed < 0) {
encoderTarget += thetaTarget - encoderTargetTheta;
targetSpeed = 0;
}

//do calculations for PD controller with new error
error = encoderTarget - (encoderActual - initialCount);
derivative = error - lastError;
lastError = error;

//At different speeds, need different gains, higher kps and kds for higher speeds ect...
if(speed <= 5) {
Torque = 3*error + 2*derivative;
} else
if (speed <= 75) {
Torque = 1.25 * error + 3 * derivative;
} else if (speed <= 100) {
Torque = 2 * error + 6 * derivative;
} else { //speed > 100
Torque = pGain * error + dGain * derivative;
}

if(error > 0) { //going in the CCW direction, Torque positive
output_low(PIN_C4);
}
else if(error < 0) {
//invert for PWM
Torque = 624 + Torque;
output_high(PIN_C4);
if(launching == 1 && thetaError < 0) { //used to tune when launching
launching = 0;
thetaTarget = 300;
targetSpeed = 10;
}
}

if(Torque < 0) Torque = 0;
if(Torque > 624) Torque = 624;
set_pwm1_duty(Torque);

}
}

#INT_RDA
void INTRDAisr() {

if(kbhit()) {
if(rsCount == 0) c_0 = getc();
else if(rsCount == 1) {
c_1 = getc();
distance = (int16)c_1 + ((int16)c_0<<8);
CalculateAndLaunch((float)distance);
}
}

rsCount++;
if(rsCount >= 2) rsCount = 0;
}
This interrupt is called when the hardware RS-232 receives a byte of data. Once two bytes of data are received (int16), the interrupt reassembles them into a single int16 and calls CalculateAndLaunch().

void main() {

setup_timer_2(T2_DIV_BY_4, 78, 16);
setup_timer_0(RTCC_EXT_L_TO_H | RTCC_DIV_1); //Counter used for Encoder A -- Up Count
setup_timer_1(T1_EXTERNAL | T1_DIV_BY_1); //Counter used for Encoder B -- Down Count

//setup offsets and intialize encoders
upCount = get_timer0();
downCount = get_timer1();
lastUpCount = upCount;
lastDownCount = downCount;

encoderActual += (upCount - downCount);

initialCount = encoderActual;

offset = encoderActual%EncCount;
if(encoderActual < 0) offset = -offset;

enable_interrupts(INT_TIMER2);
enable_interrupts(INT_RDA);
enable_interrupts(GLOBAL);
ext_int_edge(0, H_TO_L); // interrupt on INT0/RB0 pin, low to high transition
setup_ccp1(CCP_PWM);

set_pwm1_duty(0);
output_low(PIN_C4);
delay_us(10);

while(TRUE) {
delay_ms(5000);
}
}

void LaunchBall(int16 speed, int16 angle) {
targetSpeed = speed;
thetaTarget = angle;
launching=1;
}

void CalculateAndLaunch(float dist) {
dist = dist+30; //adjust for distance between ranger and motor
shotSpeed = -0.0012*(dist*dist) + 0.5884*dist + 89.678;
LaunchBall((int16)(shotSpeed/2), 3000);
}

== Results ==
In the end, the project ultimately succeeded -- baskets could be made. However, better tuning for the motor control and needs to be developed for more consistent results.

[http://www.youtube.com/watch?v=Y466dzP-qiY Link To Video]

===Problems Encountered===

*Attempting to integrate multiple pics and circuits onto one circuit board did not give good results. Ultimately, we had to use separate boards for each pic. This could be due to the effect of motor noise on our control circuitry.

*Motor control was an intense programming effort -- almost a project in its own right. Trying to combine the motor control and calibrate our throwing distance was difficult. Designing a functioning throwing device along with getting the rest of the project implemented was difficult to complete with the given time constraints.

*Many components burned out. Fly back diodes were implemented however, we still went through quite a few H-bridges. Encoder chips also burned out. The PING sensor burned out as well. We are not sure of the cause of some of these part failures.

*The length of wires for the Encoder A and B should be limited. When using long wires running from the encoder, we were not able to get our encoder chip to function properly. Replacing them with shorter wires fixed the issue. Because the signal from the encoder is switching at such high speeds, the loss in the long wires played a significant effect resulting in a faulty encoder count. Larger diameter wires may be an alternate solution to this problem.

== Notes ==
A few things we might change if we did it again:
*Simplify the motor control portion of the project. Trying to implement a speed control using the encoder count was difficult to implement. Simply using PWM to drive the motor at different speeds may have been sufficient.
*Test different wires for length and diameter for optimal performance for the Encoder A and B connections.
*Combine the PICs on one circuit board, solving the issues we encountered when attempting this.
*Perform a more detailed calibration, adjusting starting position, final launching position, and speed to get improved control over throwing distance.

Basketball

2009-03-20T07:18:22Z

John Rula: /* Code */

[[Image:Mechatronics2009Bball|right|thumb|180px]]
<br=clear all>
== Team Members ==
[[image:Team_12_Mechatronics_2009|Team Members from right to left: John, Alex, and Meredith|thumb|250px|right]]
* John Rula (Mechanical Engineering, Class of 2009)
* Alex Wojcicki (Mechanical Engineering, Class of 2009)
* Meredith Chow (Electrical Engineering, Class of 2010)

 

== Introduction ==

A throwing arm propelled by a Pittman DC brush motor is mounted on a turntable and throws the ball into the "hoop." The hoop is wrapped in reflective tape and an IR emitter, receiver pair is used to sense where the IR is reflected most (the hoop with highly reflective tape). An ultrasonic sensor then pings the hoop for the distance of the hoop. With this information, the arm is able to "make a basket."
[[Image:Mechatronics2009Bball|Entire system|left|thumb|200px]][[Image:mech2009bballcloseup|Front view|left|thumb|200px]][[Image:mech2009bballcloseupalternate|Close up|left|thumb|350px]]
 

== Mechanical Design ==
[[Image:Mechatronics2009BballCADassembly|CAD assembly|right|thumb|250px]]
The major mechanical components were machined out of clear acrylic using the laser cutter in the machine shop. Holes were machined and threaded as required. The base is a square (12" x 12") with threaded holes for attachment to the purchased turntable bearing. The turntable has threaded holes for attachment to the turntable bearing as well. Large holes were added to the turntable for screw access during assembly because once one of the parts is attached to the turntable, the screws would otherwise not be able to be tightened. The turntable features a rectangular cutout for the servo motor and threaded holes for mounting. There are additional through holes for mounting the sensor bracket and the motor supports.

Two motor supports were designed to accept the Pittman motor and hold it six inches above the turntable surface. Fasteners are inserted from below the turntable into threaded holes in the motor supports. Clamps were designed to thread onto the supports and secure the motor in place. The sensors (IR emitter/receiver pair and ultrasonic sensor) are mounted on a machined acrylic bracket that which is attached to the turntable again through fasteners inserted underneath the turntable.

The arm is also made of laser cut acrylic. It was designed with a close fit on the flat of the motor shaft and with a clamp for tightening using a threaded fastener. For manufacturing reasons, the ball holding portion of the arm was cut out of a separate piece of acrylic and secured to the end of the throwing arm.

The hoop can be anything with the highly reflective tape around it. It is suggested to have a circular profile for better performance detecting its center using the IR emitter/receiver.
[[Image:Mechatronics2009BballArmCloseup|Throwing arm attachment close up|right|thumb|250px]]

=== Mechanical Components ===

<table border=1>
<tr><th>Part</th><th>Part No.</th><th>Qty</th><th>Vendor</th><th>Price (Total)</th></tr>
<tr><td>Pittman Motor </td><td>GM8712</td><td>1</td><td>Lab</td><td>-</td></tr>
<tr><td>RC Servo Motor - Futaba </td><td>S3004</td><td>1</td><td>Lab</td><td>-</td></tr>
<tr><td>Acrylic .25" Thick, 24"X 24"</td><td>8560K357</td><td>1</td><td>[http://www.mcmaster.com/#8560K357 McMaster]</td><td>$39.63</td></tr>
<tr><td>Corrosion-Resistant Turntable</td><td>6031K17</td><td>1</td><td>[http://www.mcmaster.com/#6031k17 McMaster]</td><td>$2.42</td></tr>
<tr><td>Fasteners</td><td>-</td><td>24</td><td>Shop supply</td><td>-</td></tr>
<tr><td>Rubber Feet</td><td>-</td><td>4</td><td>Lab</td><td>-</td></tr>
</table>
 

== Electrical Design ==
The IR pair, ultrasonic, and servo have a relatively simple circuit. In the diagram below, the IR pair, ultrasonic, and servo are controlled by the program on PIC1. The IR pair and ultrasonic sensor are stacked vertically and inserted into the fitted holes on the laser cut acrylic. Because of the close proximity of the IR pair, to prevent saturation of the IR receiver, the emitter was wrapped in electrical tape. This allowed for the detection of reflected IR rather than from the emitter right below the detector. The RC servo goes through a sweep looking for the hoop. It finds the hoop by storing the location of the highest IR detection. The reflective tape used in Design Challenge 2008 and 2009 was used to wrap the hoop and is used to assist in the finding of the hoop as it reflects more IR radiation than most common objects. After making its sweep, the servo returns to the position where the most IR was detected. The ultrasonic sensor will then ping the hoop to find the distance of the hoop.

The Pittman motor, H-Bridge, and encoder chip circuit is more complex. This circuit is run by PIC2. The information collected about the hoop location is communicated from PIC1 to PIC2. The Pittman is used to launch the ball. After the hoop is found, the arm attached to the Pittman launches the ball into the hoop. The shaft rotates forward and then reverses to its previous position. The device is then ready to find the hoop and launch the ball again.

The two PICs communicated with a common ground and wire connecting RC6 and RC7 as shown in the diagram. The power supply was two 12 volt power supplies connected in series to give a total of 24 volts.

=== Electrical Components ===
<table border=1>
<tr><th>Part</th><th>Part No.</th><th>Qty</th><th>Vendor</th><th>Price (Total)</th></tr>
<tr><td>PICs</td><td>PIC18F4520</td><td>2</td><td>Lab</td><td>-</td></tr>
<tr><td>Encoder</td><td>LS7083</td><td>1</td><td>Lab</td><td>-</td></tr>
<tr><td>H-Bridge</td><td>L298N</td><td>1</td><td>Lab</td><td>-</td></tr>
<tr><td>Ping Ultrasonic Sensor</td><td>28015</td><td>1</td><td>Lab 5 supply</td><td>-</td></tr>
<tr><td>IR Emitter</td><td>QED123</td><td>1</td><td>Lab</td><td>-</td></tr>
<tr><td>IR Phototransistor</td><td>LTR-4206E</td><td>1</td><td>Lab</td><td>-</td></tr>
<tr><td>Diodes</td><td>1N4148</td><td>4</td><td>Lab</td><td>-</td></tr>
<tr><td>Resistors</td><td>47.5/150K</td><td>2</td><td>Lab</td><td>-</td></tr>
</table>
 

=== Circuit Diagram ===
[[image:team12mech2009cktwiki|Circuit diagram of how the the pics, sensors, and motor components are connected.|thumb|500px|left]][[image:mech2009bballelectronics|How the the pics, sensors, and motor components are connected.|thumb|500px|left]]

 

== Code ==

We used two PICs for this project. One ran the motor control since we wanted the smallest interrupt possible for the most accurate speed control. The other PIC ran the servo attached to the turntable as well as the infrared and ultrasonic sensors.

The motor was controlled using a PD controller which controlled both speed and position. Theory behind the controller was that if accurate speed control could be achieved along with the ability to control the release point by stopping the motor, we could control the distance the ball traveled to a high degree of accuracy having it follow simple kinematic equations. The launch was triggered when the ultrasonic sensor distance was sent to it. We opted against I2C and instead went with RS-232 for simplicity since we were only sending two bytes of data.

Full source code of the motor controller can be found [[Media:Motor-Control.c|here]].

== PD Controller ==

#INT_TIMER2 // designates that this is the routine to call when timer3 overflows
void Timer2isr() {
milsecs++;
if ((milsecs & 7) == 0) { // servo routine every 4ms is plenty. 250x/sec
//update counters and encoder
upCount = get_timer0();
encoderActual += upCount - lastUpCount; //NEW HERE (REMOVED (SIGNED INT16 CAST)
downCount = get_timer1();
encoderActual -= downCount - lastDownCount; //NEW HERE SAME AS ABOVE
lastUpCount = upCount;
lastDownCount = downCount;

theta = (int16)(encoderActual - offset) % EncCount;
thetaError = (signed int32)thetaTarget- (signed int32)theta;

//speed controls whether it is in forward or reverse
if(thetaError > 0) speed = targetSpeed;
else if(thetaError < 0) speed = -targetSpeed;

encoderTarget += speed; //need to add accuracy to speed
encoderTargetTheta = (int16)(encoderTarget) % EncCount;

if(encoderTargetTheta > thetaTarget && speed > 0) {
encoderTarget -= encoderTargetTheta - thetaTarget;
targetSpeed = 0;
} else if(encoderTargetTheta < thetaTarget && speed < 0) {
encoderTarget += thetaTarget - encoderTargetTheta;
targetSpeed = 0;
}

//do calculations for PD controller with new error
error = encoderTarget - (encoderActual - initialCount);
derivative = error - lastError;
lastError = error;

//At different speeds, need different gains, higher kps and kds for higher speeds ect...
if(speed <= 5) {
Torque = 3*error + 2*derivative;
} else
if (speed <= 75) {
Torque = 1.25 * error + 3 * derivative;
} else if (speed <= 100) {
Torque = 2 * error + 6 * derivative;
} else { //speed > 100
Torque = pGain * error + dGain * derivative;
}

if(error > 0) { //going in the CCW direction, Torque positive
output_low(PIN_C4);
}
else if(error < 0) {
//invert for PWM
Torque = 624 + Torque;
output_high(PIN_C4);
if(launching == 1 && thetaError < 0) { //used to tune when launching
launching = 0;
thetaTarget = 300;
targetSpeed = 10;
}
}

if(Torque < 0) Torque = 0;
if(Torque > 624) Torque = 624;
set_pwm1_duty(Torque);

}
}

#INT_RDA
void INTRDAisr() {

if(kbhit()) {
if(rsCount == 0) c_0 = getc();
else if(rsCount == 1) {
c_1 = getc();
distance = (int16)c_1 + ((int16)c_0<<8);
CalculateAndLaunch((float)distance);
}
}

rsCount++;
if(rsCount >= 2) rsCount = 0;
}
This interrupt is called when the hardware RS-232 receives a byte of data. Once two bytes of data are received (int16), the interrupt reassembles them into a single int16 and calls CalculateAndLaunch().

void main() {

setup_timer_2(T2_DIV_BY_4, 78, 16);
setup_timer_0(RTCC_EXT_L_TO_H | RTCC_DIV_1); //Counter used for Encoder A -- Up Count
setup_timer_1(T1_EXTERNAL | T1_DIV_BY_1); //Counter used for Encoder B -- Down Count

//setup offsets and intialize encoders
upCount = get_timer0();
downCount = get_timer1();
lastUpCount = upCount;
lastDownCount = downCount;

encoderActual += (upCount - downCount);

initialCount = encoderActual;

offset = encoderActual%EncCount;
if(encoderActual < 0) offset = -offset;

enable_interrupts(INT_TIMER2);
enable_interrupts(INT_RDA);
enable_interrupts(GLOBAL);
ext_int_edge(0, H_TO_L); // interrupt on INT0/RB0 pin, low to high transition
setup_ccp1(CCP_PWM);

set_pwm1_duty(0);
output_low(PIN_C4);
delay_us(10);

while(TRUE) {
delay_ms(5000);
}
}

void LaunchBall(int16 speed, int16 angle) {
targetSpeed = speed;
thetaTarget = angle;
launching=1;
}

void CalculateAndLaunch(float dist) {
dist = dist+30; //adjust for distance between ranger and motor
shotSpeed = -0.0012*(dist*dist) + 0.5884*dist + 89.678;
LaunchBall((int16)(shotSpeed/2), 3000);
}

== Results ==
In the end, the project ultimately succeeded -- baskets could be made. However, better tuning for the motor control and needs to be developed for more consistent results.

LINK TO VIDEO HERE

===Problems Encountered===

*Attempting to integrate multiple pics and circuits onto one circuit board did not give good results. Ultimately, we had to use separate boards for each pic. This could be due to the effect of motor noise on our control circuitry.

*Motor control was an intense programming effort -- almost a project in its own right. Trying to combine the motor control and calibrate our throwing distance was difficult. Designing a functioning throwing device along with getting the rest of the project implemented was difficult to complete with the given time constraints.

*Many components burned out. Fly back diodes were implemented however, we still went through quite a few H-bridges. Encoder chips also burned out. The PING sensor burned out as well. We are not sure of the cause of some of these part failures.

*The length of wires for the Encoder A and B should be limited. When using long wires running from the encoder, we were not able to get our encoder chip to function properly. Replacing them with shorter wires fixed the issue. Because the signal from the encoder is switching at such high speeds, the loss in the long wires played a significant effect resulting in a faulty encoder count. Larger diameter wires may be an alternate solution to this problem.

== Notes ==
A few things we might change if we did it again:
*Simplify the motor control portion of the project. Trying to implement a speed control using the encoder count was difficult to implement. Simply using PWM to drive the motor at different speeds may have been sufficient.
*Test different wires for length and diameter for optimal performance for the Encoder A and B connections.
*Combine the PICs on one circuit board, solving the issues we encountered when attempting this.
*Perform a more detailed calibration, adjusting starting position, final launching position, and speed to get improved control over throwing distance.

Basketball

2009-03-20T06:40:44Z

John Rula: /* Code */

[[Image:Mechatronics2009Bball|right|thumb|180px]]
<br=clear all>
== Team Members ==
[[image:Team_12_Mechatronics_2009|Team Members from right to left: John, Alex, and Meredith|thumb|250px|right]]
* John Rula (Mechanical Engineering, Class of 2009)
* Alex Wojcicki (Mechanical Engineering, Class of 2009)
* Meredith Chow (Electrical Engineering, Class of 2010)

 

== Introduction ==

A throwing arm propelled by a Pittman DC brush motor is mounted on a turntable and throws the ball into the "hoop." The hoop is wrapped in reflective tape and an IR emitter, receiver pair is used to sense where the IR is reflected most (the hoop with highly reflective tape). An ultrasonic sensor then pings the hoop for the distance of the hoop. With this information, the arm is able to "make a basket."
[[Image:Mechatronics2009Bball|Entire system|left|thumb|200px]][[Image:mech2009bballcloseup|Front view|left|thumb|200px]][[Image:mech2009bballcloseupalternate|Close up|left|thumb|350px]]
 

== Mechanical Design ==
[[Image:Mechatronics2009BballCADassembly|CAD assembly|right|thumb|250px]]
The major mechanical components were machined out of clear acrylic using the laser cutter in the machine shop. Holes were machined and threaded as required. The base is a square (12" x 12") with threaded holes for attachment to the purchased turntable bearing. The turntable has threaded holes for attachment to the turntable bearing as well. Large holes were added to the turntable for screw access during assembly because once one of the parts is attached to the turntable, the screws would otherwise not be able to be tightened. The turntable features a rectangular cutout for the servo motor and threaded holes for mounting. There are additional through holes for mounting the sensor bracket and the motor supports.

Two motor supports were designed to accept the Pittman motor and hold it six inches above the turntable surface. Fasteners are inserted from below the turntable into threaded holes in the motor supports. Clamps were designed to thread onto the supports and secure the motor in place. The sensors (IR emitter/receiver pair and ultrasonic sensor) are mounted on a machined acrylic bracket that which is attached to the turntable again through fasteners inserted underneath the turntable.

The arm is also made of laser cut acrylic. It was designed with a close fit on the flat of the motor shaft and with a clamp for tightening using a threaded fastener. For manufacturing reasons, the ball holding portion of the arm was cut out of a separate piece of acrylic and secured to the end of the throwing arm.

The hoop can be anything with the highly reflective tape around it. It is suggested to have a circular profile for better performance detecting its center using the IR emitter/receiver.
[[Image:Mechatronics2009BballArmCloseup|Throwing arm attachment close up|right|thumb|250px]]

=== Mechanical Components ===

<table border=1>
<tr><th>Part</th><th>Part No.</th><th>Qty</th><th>Vendor</th><th>Price (Total)</th></tr>
<tr><td>Pittman Motor </td><td>GM8712</td><td>1</td><td>Lab</td><td>-</td></tr>
<tr><td>RC Servo Motor - Futaba </td><td>S3004</td><td>1</td><td>Lab</td><td>-</td></tr>
<tr><td>Acrylic .25" Thick, 24"X 24"</td><td>8560K357</td><td>1</td><td>[http://www.mcmaster.com/#8560K357 McMaster]</td><td>$39.63</td></tr>
<tr><td>Corrosion-Resistant Turntable</td><td>6031K17</td><td>1</td><td>[http://www.mcmaster.com/#6031k17 McMaster]</td><td>$2.42</td></tr>
<tr><td>Fasteners</td><td>-</td><td>24</td><td>Shop supply</td><td>-</td></tr>
<tr><td>Rubber Feet</td><td>-</td><td>4</td><td>Lab</td><td>-</td></tr>
</table>
 

== Electrical Design ==
The IR pair, ultrasonic, and servo have a relatively simple circuit. In the diagram below, the IR pair, ultrasonic, and servo are controlled by the program on PIC1. The IR pair and ultrasonic sensor are stacked vertically and inserted into the fitted holes on the laser cut acrylic. Because of the close proximity of the IR pair, to prevent saturation of the IR receiver, the emitter was wrapped in electrical tape. This allowed for the detection of reflected IR rather than from the emitter right below the detector. The RC servo goes through a sweep looking for the hoop. It finds the hoop by storing the location of the highest IR detection. The reflective tape used in Design Challenge 2008 and 2009 was used to wrap the hoop and is used to assist in the finding of the hoop as it reflects more IR radiation than most common objects. After making its sweep, the servo returns to the position where the most IR was detected. The ultrasonic sensor will then ping the hoop to find the distance of the hoop.

The Pittman motor, H-Bridge, and encoder chip circuit is more complex. This circuit is run by PIC2. The information collected about the hoop location is communicated from PIC1 to PIC2. The Pittman is used to launch the ball. After the hoop is found, the arm attached to the Pittman launches the ball into the hoop. The shaft rotates forward and then reverses to its previous position. The device is then ready to find the hoop and launch the ball again.

The two pics communicated with a common ground and wire connecting RC6 and RC7 as shown in the diagram. The power supply was two 12 volt power supplies connected in series to give a total of 24 volts.

=== Electrical Components ===
<table border=1>
<tr><th>Part</th><th>Part No.</th><th>Qty</th><th>Vendor</th><th>Price (Total)</th></tr>
<tr><td>PICs</td><td>PIC18F4520</td><td>2</td><td>Lab</td><td>-</td></tr>
<tr><td>Encoder</td><td>LS7083</td><td>1</td><td>Lab</td><td>-</td></tr>
<tr><td>H-Bridge</td><td>L298N</td><td>1</td><td>Lab</td><td>-</td></tr>
<tr><td>Ping Ultrasonic Sensor</td><td>28015</td><td>1</td><td>Lab 5 supply</td><td>-</td></tr>
<tr><td>IR Emitter</td><td>QED123</td><td>1</td><td>Lab</td><td>-</td></tr>
<tr><td>IR Phototransistor</td><td>LTR-4206E</td><td>1</td><td>Lab</td><td>-</td></tr>
<tr><td>Diodes</td><td>1N4148</td><td>4</td><td>Lab</td><td>-</td></tr>
<tr><td>Resistors</td><td>47.5/150K</td><td>2</td><td>Lab</td><td>-</td></tr>
</table>
 

=== Circuit Diagram ===
[[image:team12mech2009cktwiki|Circuit diagram of how the the pics, sensors, and motor components are connected.|thumb|500px|left]][[image:mech2009bballelectronics|How the the pics, sensors, and motor components are connected.|thumb|500px|left]]

 

== Code ==

We used two PICs for this project. One ran the motor control since we wanted the smallest interrupt possible for the most accurate speed control. The other PIC ran the servo attached to the turntable as well as the infrared and ultrasonic sensors.

The motor was controlled using a PD controller which controlled both speed and position. Theory behind the controller was that if accurate speed control could be achieved along with the ability to control the release point by stopping the motor, we could control the distance the ball traveled to a high degree of accuracy having it follow simple kinematic equations. The launch was triggered when the ultrasonic sensor distance was sent to it. We opted against I2C and instead went with RS-232 for simplicity since we were only sending two bytes of data.

Full source code of the motor controller can be found here:[[Media:Motor-Control.c]].

#INT_RDA
void INTRDAisr() {

if(kbhit()) {
if(rsCount == 0) c_0 = getc();
else if(rsCount == 1) {
c_1 = getc();
distance = (int16)c_1 + ((int16)c_0<<8);
CalculateAndLaunch((float)distance);
}
}

rsCount++;
if(rsCount >= 2) rsCount = 0;
}
This interrupt is called when the hardware RS-232 receives a byte of data. Once two bytes of data are received (int16), the interrupt reassembles them into a single int16 and calls CalculateAndLaunch().

#INT_TIMER2 // designates that this is the routine to call when timer3 overflows
void Timer2isr() {
milsecs++;
if ((milsecs & 7) == 0) { // servo routine every 4ms is plenty. 250x/sec
//update counters and encoder
upCount = get_timer0();
encoderActual += upCount - lastUpCount; //NEW HERE (REMOVED (SIGNED INT16 CAST)
downCount = get_timer1();
encoderActual -= downCount - lastDownCount; //NEW HERE SAME AS ABOVE
lastUpCount = upCount;
lastDownCount = downCount;

theta = (int16)(encoderActual - offset) % EncCount;
thetaError = (signed int32)thetaTarget- (signed int32)theta;

//speed controls whether it is in forward or reverse
if(thetaError > 0) speed = targetSpeed;
else if(thetaError < 0) speed = -targetSpeed;

encoderTarget += speed; //need to add accuracy to speed
encoderTargetTheta = (int16)(encoderTarget) % EncCount;

if(encoderTargetTheta > thetaTarget && speed > 0) {
encoderTarget -= encoderTargetTheta - thetaTarget;
targetSpeed = 0;
} else if(encoderTargetTheta < thetaTarget && speed < 0) {
encoderTarget += thetaTarget - encoderTargetTheta;
targetSpeed = 0;
}

//do calculations for PD controller with new error
error = encoderTarget - (encoderActual - initialCount);
derivative = error - lastError;
lastError = error;

//At different speeds, need different gains, higher kps and kds for higher speeds ect...
if(speed <= 5) {
Torque = 3*error + 2*derivative;
} else
if (speed <= 75) {
Torque = 1.25 * error + 3 * derivative;
} else if (speed <= 100) {
Torque = 2 * error + 6 * derivative;
} else { //speed > 100
Torque = pGain * error + dGain * derivative;
}

if(error > 0) { //going in the CCW direction, Torque positive
output_low(PIN_C4);
}
else if(error < 0) {
//invert for PWM
Torque = 624 + Torque;
output_high(PIN_C4);
if(launching == 1 && thetaError < 0) { //used to tune when launching
launching = 0;
thetaTarget = 300;
targetSpeed = 10;
}
}

if(Torque < 0) Torque = 0;
if(Torque > 624) Torque = 624;
set_pwm1_duty(Torque);

}
}

void main() {

setup_timer_2(T2_DIV_BY_4, 78, 16);
setup_timer_0(RTCC_EXT_L_TO_H | RTCC_DIV_1); //Counter used for Encoder A -- Up Count
setup_timer_1(T1_EXTERNAL | T1_DIV_BY_1); //Counter used for Encoder B -- Down Count

//setup offsets and intialize encoders
upCount = get_timer0();
downCount = get_timer1();
lastUpCount = upCount;
lastDownCount = downCount;

encoderActual += (upCount - downCount);

initialCount = encoderActual;

offset = encoderActual%EncCount;
if(encoderActual < 0) offset = -offset;

enable_interrupts(INT_TIMER2);
enable_interrupts(INT_RDA);
enable_interrupts(GLOBAL);
ext_int_edge(0, H_TO_L); // interrupt on INT0/RB0 pin, low to high transition
setup_ccp1(CCP_PWM);

set_pwm1_duty(0);
output_low(PIN_C4);
delay_us(10);

while(TRUE) {
delay_ms(5000);
}
}

void LaunchBall(int16 speed, int16 angle) {
targetSpeed = speed;
thetaTarget = angle;
launching=1;
}

void CalculateAndLaunch(float dist) {
dist = dist+30; //adjust for distance between ranger and motor
shotSpeed = -0.0012*(dist*dist) + 0.5884*dist + 89.678;
LaunchBall((int16)(shotSpeed/2), 3000);
}

== Results ==
In the end, the project ultimately succeeded -- baskets could be made. However, better tuning for the motor control and needs to be developed for more consistent results.

LINK TO VIDEO HERE

===Problems Encountered===

*Attempting to integrate multiple pics and circuits onto one circuit board did not give good results. Ultimately, we had to use separate boards for each pic. This could be due to the effect of motor noise on our control circuitry.

*Motor control was an intense programming effort -- almost a project in its own right. Trying to combine the motor control and calibrate our throwing distance was difficult. Designing a functioning throwing device along with getting the rest of the project implemented was difficult to complete with the given time constraints.

*Many components burned out. Fly back diodes were implemented however, we still went through quite a few H-bridges. Encoder chips also burned out. The PING sensor burned out as well. We are not sure of the cause of some of these part failures.

*The length of wires for the Encoder A and B should be limited. When using long wires running from the encoder, we were not able to get our encoder chip to function properly. Replacing them with shorter wires fixed the issue. Because the signal from the encoder is switching at such high speeds, the loss in the long wires played a significant effect resulting in a faulty encoder count. Larger diameter wires may be an alternate solution to this problem.

== Notes ==
A few things we might change if we did it again:
*Simplify the motor control portion of the project. Trying to implement a speed control using the encoder count was difficult to implement. Simply using PWM to drive the motor at different speeds may have been sufficient.
*Test different wires for length and diameter for optimal performance for the Encoder A and B connections.
*Combine the PICs on one circuit board, solving the issues we encountered when attempting this.
*Perform a more detailed calibration, adjusting starting position, final launching position, and speed to get improved control over throwing distance.

File:Turntable-Control.c

2009-03-20T06:17:27Z

John Rula:

File:Motor-Control.c

2009-03-20T06:17:04Z

John Rula:

Basketball

2009-03-20T06:01:24Z

John Rula: /* Code */

[[Image:Mechatronics2009Bball|right|thumb|180px]]
<br=clear all>
== Team Members ==
[[image:Team_12_Mechatronics_2009|Team Members from right to left: John, Alex, and Meredith|thumb|250px|right]]
* John Rula (Mechanical Engineering, Class of 2009)
* Alex Wojcicki (Mechanical Engineering, Class of 2009)
* Meredith Chow (Electrical Engineering, Class of 2010)

 

== Introduction ==

A throwing arm propelled by a Pittman DC brush motor is mounted on a turntable and throws the ball into the "hoop." The hoop is wrapped in reflective tape and an IR emitter, receiver pair is used to sense where the IR is reflected most (the hoop with highly reflective tape). An ultrasonic sensor then pings the hoop for the distance of the hoop. With this information, the arm is able to "make a basket."
[[Image:Mechatronics2009Bball|Entire system|left|thumb|200px]][[Image:mech2009bballcloseup|Front view|left|thumb|200px]][[Image:mech2009bballcloseupalternate|Close up|left|thumb|350px]]
 

== Mechanical Design ==
[[Image:Mechatronics2009BballCADassembly|CAD assembly|right|thumb|250px]]
The major mechanical components were machined out of clear acrylic using the laser cutter in the machine shop. Holes were machined and threaded as required. The base is a square (12" x 12") with threaded holes for attachment to the purchased turntable bearing. The turntable has threaded holes for attachment to the turntable bearing as well. Large holes were added to the turntable for screw access during assembly because once one of the parts is attached to the turntable, the screws would otherwise not be able to be tightened. The turntable features a rectangular cutout for the servo motor and threaded holes for mounting. There are additional through holes for mounting the sensor bracket and the motor supports.

Two motor supports were designed to accept the Pittman motor and hold it six inches above the turntable surface. Fasteners are inserted from below the turntable into threaded holes in the motor supports. Clamps were designed to thread onto the supports and secure the motor in place. The sensors (IR emitter/receiver pair and ultrasonic sensor) are mounted on a machined acrylic bracket that which is attached to the turntable again through fasteners inserted underneath the turntable.

The arm is also made of laser cut acrylic. It was designed with a close fit on the flat of the motor shaft and with a clamp for tightening using a threaded fastener. For manufacturing reasons, the ball holding portion of the arm was cut out of a separate piece of acrylic and secured to the end of the throwing arm.

The hoop can be anything with the highly reflective tape around it. It is suggested to have a circular profile for better performance detecting its center using the IR emitter/receiver.
[[Image:Mechatronics2009BballArmCloseup|Throwing arm attachment close up|right|thumb|250px]]

=== Mechanical Components ===

<table border=1>
<tr><th>Part</th><th>Part No.</th><th>Qty</th><th>Vendor</th><th>Price (Total)</th></tr>
<tr><td>Pittman Motor </td><td>GM8712</td><td>1</td><td>Lab</td><td>-</td></tr>
<tr><td>RC Servo Motor - Futaba </td><td>S3004</td><td>1</td><td>Lab</td><td>-</td></tr>
<tr><td>Acrylic .25" Thick, 24"X 24"</td><td>8560K357</td><td>1</td><td>[http://www.mcmaster.com/#8560K357 McMaster]</td><td>$39.63</td></tr>
<tr><td>Corrosion-Resistant Turntable</td><td>6031K17</td><td>1</td><td>[http://www.mcmaster.com/#6031k17 McMaster]</td><td>$2.42</td></tr>
<tr><td>Fasteners</td><td>-</td><td>24</td><td>Shop supply</td><td>-</td></tr>
<tr><td>Rubber Feet</td><td>-</td><td>4</td><td>Lab</td><td>-</td></tr>
</table>
 

== Electrical Design ==
The IR pair, ultrasonic, and servo have a relatively simple circuit. In the diagram below, the IR pair, ultrasonic, and servo are controlled by the program on PIC1. The IR pair and ultrasonic sensor are stacked vertically and inserted into the fitted holes on the laser cut acrylic. Because of the close proximity of the IR pair, to prevent saturation of the IR receiver, the emitter was wrapped in electrical tape. This allowed for the detection of reflected IR rather than from the emitter right below the detector. The RC servo goes through a sweep looking for the hoop. It finds the hoop by storing the location of the highest IR detection. The reflective tape used in Design Challenge 2008 and 2009 was used to wrap the hoop and is used to assist in the finding of the hoop as it reflects more IR radiation than most common objects. After making its sweep, the servo returns to the position where the most IR was detected. The ultrasonic sensor will then ping the hoop to find the distance of the hoop.

The Pittman motor, H-Bridge, and encoder chip circuit is more complex. This circuit is run by PIC2. The information collected about the hoop location is communicated from PIC1 to PIC2. The Pittman is used to launch the ball. After the hoop is found, the arm attached to the Pittman launches the ball into the hoop. The shaft rotates forward and then reverses to its previous position. The device is then ready to find the hoop and launch the ball again.

The two pics communicated with a common ground and wire connecting RC6 and RC7 as shown in the diagram. The power supply was two 12 volt power supplies connected in series to give a total of 24 volts.

=== Electrical Components ===
<table border=1>
<tr><th>Part</th><th>Part No.</th><th>Qty</th><th>Vendor</th><th>Price (Total)</th></tr>
<tr><td>PICs</td><td>PIC18F4520</td><td>2</td><td>Lab</td><td>-</td></tr>
<tr><td>Encoder</td><td>LS7083</td><td>1</td><td>Lab</td><td>-</td></tr>
<tr><td>H-Bridge</td><td>L298N</td><td>1</td><td>Lab</td><td>-</td></tr>
<tr><td>Ping Ultrasonic Sensor</td><td>28015</td><td>1</td><td>Lab 5 supply</td><td>-</td></tr>
<tr><td>IR Emitter</td><td>QED123</td><td>1</td><td>Lab</td><td>-</td></tr>
<tr><td>IR Phototransistor</td><td>LTR-4206E</td><td>1</td><td>Lab</td><td>-</td></tr>
<tr><td>Diodes</td><td>1N4148</td><td>4</td><td>Lab</td><td>-</td></tr>
<tr><td>Resistors</td><td>47.5/150K</td><td>2</td><td>Lab</td><td>-</td></tr>
</table>
 

=== Circuit Diagram ===
[[image:team12mech2009cktwiki|Circuit diagram of how the the pics, sensors, and motor components are connected.|thumb|500px|left]][[image:mech2009bballelectronics|How the the pics, sensors, and motor components are connected.|thumb|500px|left]]

 

== Code ==
#include <18f4520.h>
#fuses HS,NOLVP,NOWDT,NOPROTECT
#use delay(clock=40000000)
#use rs232(baud=19200, UART1)

int16 EncCount = 9984; //Number of Encoder Counts per Rev
float pGain =1.25; //Kp for proportional control
float dGain =3; //Kd for derivative control
signed int32 encoderTarget = 0; //Target for encoder counts to reach
signed int32 error = 0; //EncoderTarget - EncoderActual
signed int32 lastError; //Previous error term
signed int32 encoderActual = 0; //Actual position of shaft in total encoder counts
signed int32 initialCount = 0; //Encoder count when system boots
signed int32 speed = 0; //Speed of rotation 250*speed = encoder counts per second
signed int32 targetSpeed = 0; //What speed should be set to
signed int32 Torque; //PWM value
signed int32 derivative = 0; //Derivative term
signed int32 offset = 0; //Value to set theta = 0 from when system starts
int16 theta=0; //Value between 0->EncCount representing angle from 0 to 360
int16 thetaTarget = 0; //Position Control Target
int16 encoderTargetTheta =0 ; //Theta value of encoderTarget after speed has been added
signed int32 thetaError = 0; // == thetaTarget - theta
int16 upCount = 0, downCount = 0, lastUpCount = 0, lastDownCount = 0; //Encoder count variables
int launching = 0; //Indicates whether arm is on up-swing of launch (1), (0) otherwise
int32 milsecs = 0; //Increments at each interrupt
int rsCount = 0; //Used to track characters coming over RS-232
char c_0 = 0;
char c_1 = 0;
int16 distance =0; //Distance sent to PIC over RS-232
float shotSpeed; //Speed determined by CalculateAndLaunch()

void LaunchBall(int16 speed, int16 angle);
void CalculateAndLaunch(float dist);

#INT_RDA
void INTRDAisr() {

if(kbhit()) {
if(rsCount == 0) c_0 = getc();
else if(rsCount == 1) {
c_1 = getc();
distance = (int16)c_1 + ((int16)c_0<<8);
CalculateAndLaunch((float)distance);
}
}

rsCount++;
if(rsCount >= 2) rsCount = 0;
}

#INT_TIMER2 // designates that this is the routine to call when timer3 overflows
void Timer2isr() {
milsecs++;
if ((milsecs & 7) == 0) { // servo routine every 4ms is plenty. 250x/sec
//update counters and encoder
upCount = get_timer0();
encoderActual += upCount - lastUpCount; //NEW HERE (REMOVED (SIGNED INT16 CAST)
downCount = get_timer1();
encoderActual -= downCount - lastDownCount; //NEW HERE SAME AS ABOVE
lastUpCount = upCount;
lastDownCount = downCount;

theta = (int16)(encoderActual - offset) % EncCount;
thetaError = (signed int32)thetaTarget- (signed int32)theta;

//speed controls whether it is in forward or reverse
if(thetaError > 0) speed = targetSpeed;
else if(thetaError < 0) speed = -targetSpeed;

encoderTarget += speed; //need to add accuracy to speed
encoderTargetTheta = (int16)(encoderTarget) % EncCount;

if(encoderTargetTheta > thetaTarget && speed > 0) {
encoderTarget -= encoderTargetTheta - thetaTarget;
targetSpeed = 0;
} else if(encoderTargetTheta < thetaTarget && speed < 0) {
encoderTarget += thetaTarget - encoderTargetTheta;
targetSpeed = 0;
}

//do calculations for PD controller with new error
error = encoderTarget - (encoderActual - initialCount);
derivative = error - lastError;
lastError = error;

//At different speeds, need different gains, higher kps and kds for higher speeds ect...
if(speed <= 5) {
Torque = 3*error + 2*derivative;
} else
if (speed <= 75) {
Torque = 1.25 * error + 3 * derivative;
} else if (speed <= 100) {
Torque = 2 * error + 6 * derivative;
} else { //speed > 100
Torque = pGain * error + dGain * derivative;
}

if(error > 0) { //going in the CCW direction, Torque positive
output_low(PIN_C4);
}
else if(error < 0) {
//invert for PWM
Torque = 624 + Torque;
output_high(PIN_C4);
if(launching == 1 && thetaError < 0) { //used to tune when launching
launching = 0;
thetaTarget = 300;
targetSpeed = 10;
}
}

if(Torque < 0) Torque = 0;
if(Torque > 624) Torque = 624;
set_pwm1_duty(Torque);

}
}

void main() {

setup_timer_2(T2_DIV_BY_4, 78, 16);
setup_timer_0(RTCC_EXT_L_TO_H | RTCC_DIV_1); //Counter used for Encoder A -- Up Count
setup_timer_1(T1_EXTERNAL | T1_DIV_BY_1); //Counter used for Encoder B -- Down Count

//setup offsets and intialize encoders
upCount = get_timer0();
downCount = get_timer1();
lastUpCount = upCount;
lastDownCount = downCount;

encoderActual += (upCount - downCount);

initialCount = encoderActual;

offset = encoderActual%EncCount;
if(encoderActual < 0) offset = -offset;

enable_interrupts(INT_TIMER2);
enable_interrupts(INT_RDA);
enable_interrupts(GLOBAL);
ext_int_edge(0, H_TO_L); // interrupt on INT0/RB0 pin, low to high transition
setup_ccp1(CCP_PWM);

set_pwm1_duty(0);
output_low(PIN_C4);
delay_us(10);

while(TRUE) {
delay_ms(5000);
}
}

void LaunchBall(int16 speed, int16 angle) {
targetSpeed = speed;
thetaTarget = angle;
launching=1;
}

void CalculateAndLaunch(float dist) {
dist = dist+30; //adjust for distance between ranger and motor
shotSpeed = -0.0012*(dist*dist) + 0.5884*dist + 89.678;
LaunchBall((int16)(shotSpeed/2), 3000);
}

== Results ==
In the end, the project ultimately succeeded -- baskets could be made. However, better tuning for the motor control and needs to be developed for more consistent results.

LINK TO VIDEO HERE

===Problems Encountered===

*Attempting to integrate multiple pics and circuits onto one circuit board did not give good results. Ultimately, we had to use separate boards for each pic. This could be due to the effect of motor noise on our control circuitry.

*Motor control was an intense programming effort -- almost a project in its own right. Trying to combine the motor control and calibrate our throwing distance was difficult. Designing a functioning throwing device along with getting the rest of the project implemented was difficult to complete with the given time constraints.

*Many components burned out. Fly back diodes were implemented however, we still went through quite a few H-bridges. Encoder chips also burned out. The PING sensor burned out as well. We are not sure of the cause of some of these part failures.

*The length of wires for the Encoder A and B should be limited. When using long wires running from the encoder, we were not able to get our encoder chip to function properly. Replacing them with shorter wires fixed the issue. Because the signal from the encoder is switching at such high speeds, the loss in the long wires played a significant effect resulting in a faulty encoder count. Larger diameter wires may be an alternate solution to this problem.

== Notes ==
A few things we might change if we did it again:
*Simplify the motor control portion of the project. Trying to implement a speed control using the encoder count was difficult to implement. Simply using PWM to drive the motor at different speeds may have been sufficient.
*Test different wires for length and diameter for optimal performance for the Encoder A and B connections.
*Combine the PICs on one circuit board, solving the issues we encountered when attempting this.
*Perform a more detailed calibration, adjusting starting position, final launching position, and speed to get improved control over throwing distance.

Basketball

2009-03-20T05:34:42Z

John Rula: /* Code */

[[Image:Mechatronics2009Bball|right|thumb|180px]]
<br=clear all>
== Team Members ==
[[image:Team_12_Mechatronics_2009|Team Members from right to left: John, Alex, and Meredith|thumb|250px|right]]
* John Rula (Mechanical Engineering, Class of 2009)
* Alex Wojcicki (Mechanical Engineering, Class of 2009)
* Meredith Chow (Electrical Engineering, Class of 2010)

 

== Introduction ==

A throwing arm propelled by a Pittman DC brush motor is mounted on a turntable and throws the ball into the "hoop." The hoop is wrapped in reflective tape and an IR emitter, receiver pair is used to sense where the IR is reflected most (the hoop with highly reflective tape). An ultrasonic sensor then pings the hoop for the distance of the hoop. With this information, the arm is able to "make a basket."
[[Image:Mechatronics2009Bball|Entire system|left|thumb|200px]][[Image:mech2009bballcloseup|Front view|left|thumb|200px]][[Image:mech2009bballcloseupalternate|Close up|left|thumb|350px]]
 

== Mechanical Design ==
[[Image:Mechatronics2009BballCADassembly|CAD assembly|right|thumb|250px]]
The major mechanical components were machined out of clear acrylic using the laser cutter in the machine shop. Holes were machined and threaded as required. The base is a square (12" x 12") with threaded holes for attachment to the purchased turntable bearing. The turntable has threaded holes for attachment to the turntable bearing as well. Large holes were added to the turntable for screw access during assembly because once one of the parts is attached to the turntable, the screws would otherwise not be able to be tightened. The turntable features a rectangular cutout for the servo motor and threaded holes for mounting. There are additional through holes for mounting the sensor bracket and the motor supports.

Two motor supports were designed to accept the Pittman motor and hold it six inches above the turntable surface. Fasteners are inserted from below the turntable into threaded holes in the motor supports. Clamps were designed to thread onto the supports and secure the motor in place. The sensors (IR emitter/receiver pair and ultrasonic sensor) are mounted on a machined acrylic bracket that which is attached to the turntable again through fasteners inserted underneath the turntable.

The arm is also made of laser cut acrylic. It was designed with a close fit on the flat of the motor shaft and with a clamp for tightening using a threaded fastener. For manufacturing reasons, the ball holding portion of the arm was cut out of a separate piece of acrylic and secured to the end of the throwing arm.

The hoop can be anything with the highly reflective tape around it. It is suggested to have a circular profile for better performance detecting its center using the IR emitter/receiver.
[[Image:Mechatronics2009BballArmCloseup|Throwing arm attachment close up|right|thumb|250px]]

=== Mechanical Components ===

<table border=1>
<tr><th>Part</th><th>Part No.</th><th>Qty</th><th>Vendor</th><th>Price (Total)</th></tr>
<tr><td>Pittman Motor </td><td>GM8712</td><td>1</td><td>Lab</td><td>-</td></tr>
<tr><td>RC Servo Motor - Futaba </td><td>S3004</td><td>1</td><td>Lab</td><td>-</td></tr>
<tr><td>Acrylic .25" Thick, 24"X 24"</td><td>8560K357</td><td>1</td><td>[http://www.mcmaster.com/#8560K357 McMaster]</td><td>$39.63</td></tr>
<tr><td>Corrosion-Resistant Turntable</td><td>6031K17</td><td>1</td><td>[http://www.mcmaster.com/#6031k17 McMaster]</td><td>$2.42</td></tr>
<tr><td>Fasteners</td><td>-</td><td>24</td><td>Shop supply</td><td>-</td></tr>
<tr><td>Rubber Feet</td><td>-</td><td>4</td><td>Lab</td><td>-</td></tr>
</table>
 

== Electrical Design ==
The IR pair, ultrasonic, and servo have a relatively simple circuit. In the diagram below, the IR pair, ultrasonic, and servo are controlled by the program on PIC1. The IR pair and ultrasonic sensor are stacked vertically and inserted into the fitted holes on the laser cut acrylic. Because of the close proximity of the IR pair, to prevent saturation of the IR receiver, the emitter was wrapped in electrical tape. This allowed for the detection of reflected IR rather than from the emitter right below the detector. The RC servo goes through a sweep looking for the hoop. It finds the hoop by storing the location of the highest IR detection. The reflective tape used in Design Challenge 2008 and 2009 was used to wrap the hoop and is used to assist in the finding of the hoop as it reflects more IR radiation than most common objects. After making its sweep, the servo returns to the position where the most IR was detected. The ultrasonic sensor will then ping the hoop to find the distance of the hoop.

The Pittman motor, H-Bridge, and encoder chip circuit is more complex. This circuit is run by PIC2. The information collected about the hoop location is communicated from PIC1 to PIC2. The Pittman is used to launch the ball. After the hoop is found, the arm attached to the Pittman launches the ball into the hoop. The shaft rotates forward and then reverses to its previous position. The device is then ready to find the hoop and launch the ball again.

The two pics communicated with a common ground and wire connecting RC6 and RC7 as shown in the diagram. The power supply was two 12 volt power supplies connected in series to give a total of 24 volts.

=== Electrical Components ===
<table border=1>
<tr><th>Part</th><th>Part No.</th><th>Qty</th><th>Vendor</th><th>Price (Total)</th></tr>
<tr><td>PICs</td><td>PIC18F4520</td><td>2</td><td>Lab</td><td>-</td></tr>
<tr><td>Encoder</td><td>LS7083</td><td>1</td><td>Lab</td><td>-</td></tr>
<tr><td>H-Bridge</td><td>L298N</td><td>1</td><td>Lab</td><td>-</td></tr>
<tr><td>Ping Ultrasonic Sensor</td><td>28015</td><td>1</td><td>Lab 5 supply</td><td>-</td></tr>
<tr><td>IR Emitter</td><td>QED123</td><td>1</td><td>Lab</td><td>-</td></tr>
<tr><td>IR Phototransistor</td><td>LTR-4206E</td><td>1</td><td>Lab</td><td>-</td></tr>
<tr><td>Diodes</td><td>1N4148</td><td>4</td><td>Lab</td><td>-</td></tr>
<tr><td>Resistors</td><td>47.5/150K</td><td>2</td><td>Lab</td><td>-</td></tr>
</table>
 

=== Circuit Diagram ===
[[image:team12mech2009cktwiki|Circuit diagram of how the the pics, sensors, and motor components are connected.|thumb|500px|left]][[image:mech2009bballelectronics|How the the pics, sensors, and motor components are connected.|thumb|500px|left]]

 

== Code ==
#include <18f4520.h>
#fuses HS,NOLVP,NOWDT,NOPROTECT
#use delay(clock=40000000)
#use rs232(baud=19200, UART1)

int16 EncCount = 9984;
float pGain =1.25;
float dGain =3;
signed int32 encoderTarget = 0;
signed int32 error = 0;
signed int32 lastError;
signed int32 encoderActual = 0;
signed int32 initialCount = 0;
signed int32 speed = 0;
signed int32 targetSpeed = 0;
signed int32 LeftError, LeftErrorLastTime=0, LeftIntegral, LeftDerivative, LeftTorque;
signed int32 derivative = 0;
signed int32 offset = 0;
int16 theta=0;
int16 thetaTarget = 0;
int16 encoderTargetTheta =0 ;
signed int32 thetaError = 0;
int16 upCount = 0, downCount = 0, lastUpCount = 0, lastDownCount = 0;
int launching = 0;
int32 milsecs = 0;
int rsCount = 0;
char c_0 = 0;
char c_1 = 0;
int16 distance =0 ;
float shotSpeed;

void LaunchBall(int16 speed, int16 angle);
void CalculateAndLaunch(float dist);

#INT_RDA
void INTRDAisr() {

if(kbhit()) {
if(rsCount == 0) c_0 = getc();
else if(rsCount == 1) {
c_1 = getc();
distance = (int16)c_1 + ((int16)c_0<<8);
CalculateAndLaunch((float)distance);
}
}

rsCount++;
if(rsCount >= 2) rsCount = 0;

}

#INT_TIMER2 // designates that this is the routine to call when timer3 overflows
void Timer2isr() {
milsecs++;
if ((milsecs & 7) == 0) { // servo routine every 4ms is plenty. 250x/sec

//update counters and encoder
upCount = get_timer0();
encoderActual += upCount - lastUpCount; //NEW HERE (REMOVED (SIGNED INT16 CAST)
downCount = get_timer1();
encoderActual -= downCount - lastDownCount; //NEW HERE SAME AS ABOVE

lastUpCount = upCount;
lastDownCount = downCount;

theta = (int16)(encoderActual - offset) % EncCount;
thetaError = (signed int32)thetaTarget- (signed int32)theta;

//speed controls whether it is in forward or reverse
if(thetaError > 0) speed = targetSpeed;
else if(thetaError < 0) speed = -targetSpeed;

encoderTarget += speed; //need to add accuracy to speed

encoderTargetTheta = (int16)(encoderTarget) % EncCount;

if(encoderTargetTheta > thetaTarget && speed > 0) {
encoderTarget -= encoderTargetTheta - thetaTarget;
targetSpeed = 0;

} else if(encoderTargetTheta < thetaTarget && speed < 0) {
encoderTarget += thetaTarget - encoderTargetTheta;
targetSpeed = 0;
}

encoderTargetTheta = (int16)(encoderTarget) % EncCount;

//do calculations for PD controller with new error
error = encoderTarget - (encoderActual - initialCount);

derivative = error - lastError;
lastError = error;

//At different speeds, need different gains, higher kps and kds for higher speeds ect...
if(speed <= 5) {
LeftTorque = 3*error + 2*derivative;
} else
if (speed <= 75) {
LeftTorque = 1.25 * error + 3 * derivative; // good luck w/o floats...
} else if (speed <= 100) {
LeftTorque = 2 * error + 6 * derivative; // good luck w/o floats...
} else { //speed > 100
LeftTorque = pGain * error + dGain * derivative; // good luck w/o floats...
}

if(error > 0) { //going in the CCW direction, Left torque positive
output_low(PIN_C4);
}
else if(error < 0) {
//invert for PWM
LeftTorque = 624 + LeftTorque;
output_high(PIN_C4);
if(launching == 1 && thetaError < 0) { //used to tune when launching
launching = 0;
thetaTarget = 300;
targetSpeed = 10;
}
}

if(LeftTorque < 0) LeftTorque = 0;
if(LeftTorque > 624) LeftTorque = 624;

set_pwm1_duty(LeftTorque);

output_d(encoderActual);

}
}

void main() {

setup_timer_2(T2_DIV_BY_4, 78, 16); // clock at 16KHz, interrupt every 4*25nS * 4 * 78 * 16 = 0.5mS

setup_timer_0(RTCC_EXT_L_TO_H | RTCC_DIV_1); // default is divide by two!
setup_timer_1(T1_EXTERNAL | T1_DIV_BY_1); // default is divide by one

//setup offsets and intialize encoders
upCount = get_timer0();
downCount = get_timer1();
lastUpCount = upCount;
lastDownCount = downCount;

encoderActual += (upCount - downCount);

initialCount = encoderActual;

offset = encoderActual%EncCount;
if(encoderActual < 0) offset = -offset;

enable_interrupts(INT_TIMER2);
enable_interrupts(INT_RDA);
enable_interrupts(GLOBAL);

ext_int_edge(0, H_TO_L); // interrupt on INT0/RB0 pin, low to high transition

setup_ccp1(CCP_PWM);
set_pwm1_duty(0);
delay_us(10);

output_low(PIN_C4);

while(TRUE) {
delay_ms(5000);
}
}

void LaunchBall(int16 speed, int16 angle) {
targetSpeed = speed;
thetaTarget = angle;
launching=1;
}

void CalculateAndLaunch(float dist) {
dist = dist+30; //adjust for distance between ranger and motor
shotSpeed = -0.0012*(dist*dist) + 0.5884*dist + 89.678;
LaunchBall((int16)(shotSpeed/2), 3000);
}

== Results ==
In the end, the project ultimately succeeded -- baskets could be made. However, better tuning for the motor control and needs to be developed for more consistent results.

LINK TO VIDEO HERE

===Problems Encountered===

*Attempting to integrate multiple pics and circuits onto one circuit board did not give good results. Ultimately, we had to use separate boards for each pic. This could be due to the effect of motor noise on our control circuitry.

*Motor control was an intense programming effort -- almost a project in its own right. Trying to combine the motor control and calibrate our throwing distance was difficult. Designing a functioning throwing device along with getting the rest of the project implemented was difficult to complete with the given time constraints.

*Many components burned out. Fly back diodes were implemented however, we still went through quite a few H-bridges. Encoder chips also burned out. The PING sensor burned out as well. We are not sure of the cause of some of these part failures.

*The length of wires for the Encoder A and B should be limited. When using long wires running from the encoder, we were not able to get our encoder chip to function properly. Replacing them with shorter wires fixed the issue. Because the signal from the encoder is switching at such high speeds, the loss in the long wires played a significant effect resulting in a faulty encoder count. Larger diameter wires may be an alternate solution to this problem.

== Notes ==
A few things we might change if we did it again:
*Simplify the motor control portion of the project. Trying to implement a speed control using the encoder count was difficult to implement. Simply using PWM to drive the motor at different speeds may have been sufficient.
*Test different wires for length and diameter for optimal performance for the Encoder A and B connections.
*Combine the PICs on one circuit board, solving the issues we encountered when attempting this.
*Perform a more detailed calibration, adjusting starting position, final launching position, and speed to get improved control over throwing distance.

Fingertip laser light sensor

2009-02-12T18:32:12Z

John Rula: /* Circuit */

== Original Assignment ==

I will provide you with a laser that emits a sheet of laser light and a phototransistor for detecting this light. You will investigate their use in developing a fingertip position sensor that senses distance to the finger based on reflected laser light. Your job is to design a sensor circuit and determine the analog voltage readings you get as a function of (1) your finger position and (2) the sensor's location relative to the emitter. You will likely display your results by communicating with a PC or by writing to an LCD (see, e.g., [[C Example: Serial LCD]] or [[C Example: Parallel Interfacing with LCDs]]).

== Overview ==
[[Image:Setup.jpg|thumb|right|250px|Experimental Setup]]
A laser that emits a sheet of laser light and phototransistor were the main components of this lab. They are used to investigate a fingertip position sensor that senses the position of the finger based on reflected laser light. The laser is positioned so that it emits a sheet of light just above the plane of the table. If a finger is placed within this field of light, then it will reflect the light back towards the laser. A phototransistor was used to detect the light reflected from the finger. A sensor circuit was designed to take analog voltage readings from the phototransistor with the intention of relating the intensity of reflected light to both the (1) finger position and (2) the phototransistor's location relative to the emitter. The results were displayed by communicating with a PC.

To begin we placed the phototransistor directly adjacent to the laser in order that the distance from the laser to the finger would be approximately the same as the distance from the finger back to the phototransistor. In our first experimental setup, we tested four different resistors in the phototransistor sensing circuit while varying the finger position directly away from the laser (up/down in the figure) in order to get an idea of the level of sensitivity that each resistor would provide. Our second experiment involved moving the finger perpindicular to the laser (left/right in the figure) at three fixed intervals.

Then, we manipulated the position of the phototransistor to see if we could get an improved sensitivity from our sensing circuit. In our third experiment, we put a shield (electrical tape) on the backside of the phototransistor and moved it directly out (down in the figure) into the sheet of light at different positions and varied the finger position in the same (up/down) direction. In the fourth experiment, we moved the transistor directly to the left of the laser in several positions and measured the variation as the finger moved in the up/down direction.

'''Important Note: '''The effect of ambient light on the photodiode is significant. In fact, the shadow cast on the photodiode when a finger was placed nearby had a larger effect than the total light reflected from the finger. In order to compensate for this, it was necessary to strobe the laser. The measurement when the laser was on was compared to the measurement when the laser was off to compensate for the ambient light and determine the light intensity contributed by just the laser. (See Code)

== Circuit ==
[[Image:detector circuit.jpg]]

== Code ==
The code involved in the fingertip detector strobes the laser every 10ms to get a reading of both the laser light and the ambient light on the phototransitsor. The ambient light is then subtracted out to give only the amount of laser light reflected. Due to the noise involved in the reading from the phototransistor, we averaged every 20 readings for each output.

#include <18f4520.h>
#DEVICE ADC=10 //10-bit ADC
#fuses HS,NOLVP,NOWDT,NOPROTECT
#use delay(clock=40000000) // 40 MHz crystal on PCB
#use rs232(baud=19200, UART1) // hardware uart
int16 reading;
int16 ambient;
int32 reading_sum=0;
int32 ambient_sum=0;
int i=0;
float dist=0;
int16 diff = 0;
void main()
{
setup_adc_ports(AN0_TO_AN3); //setup ADC ports
setup_adc(ADC_CLOCK_INTERNAL);
while(TRUE) {
set_adc_channel(0); //set adc channel
output_high(PIN_C0); //strobe the laser high for 10 ms
delay_ms(10);
reading = read_adc(); //take phototransistor reading with reflected laser light
reading_sum += reading; //add reading to reading_sum which we will average later
output_low(PIN_C0); //strobe the laser low for 10 ms
delay_ms(10);
ambient = read_adc(); //take reading of ambient light
ambient_sum += ambient; //add ambient reading to ambient_sum which we will average later
i += 1;
//Due to the inherent noise of the system, we average 20 readings for each output
if(i >= 20) { //number 20 is number that we average each cycle
reading = reading_sum / i;
ambient = ambient_sum / i;
diff = reading - ambient;
dist = 395/(float)diff; //close approximation of distance curve using 19.5K resistor
//print results over the serial port
printf("L = %Lu A = %Lu Diff = %Lu Dist = %f\r\n", reading, ambient, diff, dist);
//reset values of I, reading_sum, and ambient_sum
i=0;
reading_sum = 0;
ambient_sum = 0;
}
}
}

== Data ==
[[Image:Resistor Selection.jpg|thumb|left|300px|Click to Enlarge]]
'''First Experiment: '''The phototransistor is placed directly adjacent to the laser. The finger was moved directly away from the laser (up/down in Experimental Setup above). Different resistors were used to investigate sensitivity.

Note: In all experiments voltage was measured on a scale of 0V to 5V and recorded as a 10-bit integer (0-1023).
 

[[Image:Distance Calibration.jpg|thumb|left|300px|Click to Enlarge]]
Distance calibration using 19.5 K-Ohm resistor

The fit applied to the curve was of the form: <math>I=A*d^B</math>
where I is the intensity of light (measured as a voltage), d is the distance, and A and B are constants.

The best fit to the data was A = 395 and B = -1 <math>(R^2=.974)</math>

The resulting calibration used to calculate distance from the intensity is <math>d=I/395</math>
 

[[Image:Varying Horizontal Position.jpg|thumb|left|300px|Click to Enlarge]]
'''Second Experiment: '''The phototransistor is placed directly adjacent to the laser. The finger was placed at fixed distances from the laser (1 cm, 2.5 cm, 5 cm) and then moved horizontally (left/right in Experimental Setup above). Using 19.5 K-Ohm resistor.

Note: The negative values are on the same side of the laser as the phototransistor. This results in a shorter distance for the light to travel and a greater intensity on the left side.
 

[[Image:Varying Phototransistor Position.jpg|thumb|left|300px|Click to Enlarge]]
'''Third Experiment: '''The phototransistor was moved directly out into the sheet of light (up/down in Experimental Setup). The finger was moved in same up/down direction. Using 19.5 K-Ohm resistor.
 

[[Image:Varying Phototransistor Position Horizontally.jpg|thumb|left|300px|Click to Enlarge]]
'''Fourth Experiment: '''The phototransistor was moved to the left of the laser. The finger was moved in the up/down direction. Using 19.5 K-Ohm Resistor.
 

== Limitations and Environmental Factors ==

There were a few environmental factors that affect the sensors:

1) Ambient light: The overhead light saturated the phototransistor and so the laser was pulsed (the pic was programmed to strobe the laser) in an effort to provide a noticeable difference between the ambient and laser light. As noted above, a finger in front of the transistor cast a shadow which had a larger effect (due to the blocking of the ambient light)than the actual blocking of the laser. Be aware that as the experiment is done any shadow cast on the sensors by a finger or body part will affect the ambient light sensed by the phototransistor and should be taken into account.

2) Lower resistances can be used for the phototransistor to prevent saturation but this also causes a reduced sensitivity to light.

3) The sheet laser provided was not uniform. There were different intensities of light across the line emitted.

4) There is a limited range in which the fingertip laser light sensor is accurate. Using the code and setup described above, there was accurate sensing of the fingertip directly in front of the laser and phototransistor to about seven centimeters.

5) The same finger and the fingernail side were used for all of the experiments. Results may be affected by testing with different fingers or whether it is the fingernail side or not, or a side of the finger. Instead of a finger, a white plastic dowel could be used as a control initially and then a finger used with more progress.

File:Detector circuit.jpg

2009-02-12T18:31:31Z

John Rula: Circuit Diagram

Circuit Diagram

Fingertip laser light sensor

2009-02-12T17:50:28Z

John Rula: /* Code */

== Original Assignment ==

I will provide you with a laser that emits a sheet of laser light and a phototransistor for detecting this light. You will investigate their use in developing a fingertip position sensor that senses distance to the finger based on reflected laser light. Your job is to design a sensor circuit and determine the analog voltage readings you get as a function of (1) your finger position and (2) the sensor's location relative to the emitter. You will likely display your results by communicating with a PC or by writing to an LCD (see, e.g., [[C Example: Serial LCD]] or [[C Example: Parallel Interfacing with LCDs]]).

== Overview ==
[[Image:Setup.jpg|thumb|right|250px|Experimental Setup]]
A laser that emits a sheet of laser light and phototransistor were the main components of this lab. They are used to investigate a fingertip position sensor that senses the position of the finger based on reflected laser light. The laser is positioned so that it emits a sheet of light just above the plane of the table. If a finger is placed within this field of light, then it will reflect the light back towards the laser. A phototransistor was used to detect the light reflected from the finger. A sensor circuit was designed to take analog voltage readings from the phototransistor with the intention of relating the intensity of reflected light to both the (1) finger position and (2) the phototransistor's location relative to the emitter. The results were displayed by communicating with a PC.

To begin we placed the phototransistor directly adjacent to the laser in order that the distance from the laser to the finger would be approximately the same as the distance from the finger back to the phototransistor. In our first experimental setup, we tested four different resistors in the phototransistor sensing circuit while varying the finger position directly away from the laser (up/down in the figure) in order to get an idea of the level of sensitivity that each resistor would provide. Our second experiment involved moving the finger perpindicular to the laser (left/right in the figure) at three fixed intervals.

Then, we manipulated the position of the phototransistor to see if we could get an improved sensitivity from our sensing circuit. In our third experiment, we put a shield (electrical tape) on the backside of the phototransistor and moved it directly out (down in the figure) into the sheet of light at different positions and varied the finger position in the same (up/down) direction. In the fourth experiment, we moved the transistor directly to the left of the laser in several positions and measured the variation as the finger moved in the up/down direction.

'''Important Note: '''The effect of ambient light on the photodiode is significant. In fact, the shadow cast on the photodiode when a finger was placed nearby had a larger effect than the total light reflected from the finger. In order to compensate for this, it was necessary to strobe the laser. The measurement when the laser was on was compared to the measurement when the laser was off to compensate for the ambient light and determine the light intensity contributed by just the laser. (See Code)

== Circuit ==

== Code ==
The code involved in the fingertip detector strobes the laser every 10ms to get a reading of both the laser light and the ambient light on the phototransitsor. The ambient light is then subtracted out to give only the amount of laser light reflected. Due to the noise involved in the reading from the phototransistor, we averaged every 20 readings for each output.

#include <18f4520.h>
#DEVICE ADC=10 //10-bit ADC
#fuses HS,NOLVP,NOWDT,NOPROTECT
#use delay(clock=40000000) // 40 MHz crystal on PCB
#use rs232(baud=19200, UART1) // hardware uart
int16 reading;
int16 ambient;
int32 reading_sum=0;
int32 ambient_sum=0;
int i=0;
float dist=0;
int16 diff = 0;
void main()
{
setup_adc_ports(AN0_TO_AN3); //setup ADC ports
setup_adc(ADC_CLOCK_INTERNAL);
while(TRUE) {
set_adc_channel(0); //set adc channel
output_high(PIN_C0); //strobe the laser high for 10 ms
delay_ms(10);
reading = read_adc(); //take phototransistor reading with reflected laser light
reading_sum += reading; //add reading to reading_sum which we will average later
output_low(PIN_C0); //strobe the laser low for 10 ms
delay_ms(10);
ambient = read_adc(); //take reading of ambient light
ambient_sum += ambient; //add ambient reading to ambient_sum which we will average later
i += 1;
//Due to the inherent noise of the system, we average 20 readings for each output
if(i >= 20) { //number 20 is number that we average each cycle
reading = reading_sum / i;
ambient = ambient_sum / i;
diff = reading - ambient;
dist = 395/(float)diff; //close approximation of distance curve using 19.5K resistor
//print results over the serial port
printf("L = %Lu A = %Lu Diff = %Lu Dist = %f\r\n", reading, ambient, diff, dist);
//reset values of I, reading_sum, and ambient_sum
i=0;
reading_sum = 0;
ambient_sum = 0;
}
}
}

== Data ==
[[Image:Resistor Selection.jpg|thumb|left|300px|Click to Enlarge]]
'''First Experiment: '''The phototransistor is placed directly adjacent to the laser. The finger was moved directly away from the laser (up/down in Experimental Setup above). Different resistors were used to investigate sensitivity.

Note: In all experiments voltage was measured on a scale of 0V to 5V and recorded as a 10-bit integer (0-1023).
 

[[Image:Distance Calibration.jpg|thumb|left|300px|Click to Enlarge]]
Distance calibration using 19.5 K-Ohm resistor

The fit applied to the curve was of the form: <math>I=A*d^B</math>
where I is the intensity of light (measured as a voltage), d is the distance, and A and B are constants.

The best fit to the data was A = 395 and B = -1 <math>(R^2=.974)</math>

The resulting calibration used to calculate distance from the intensity is <math>d=I/395</math>
 

[[Image:Varying Horizontal Position.jpg|thumb|left|300px|Click to Enlarge]]
'''Second Experiment: '''The phototransistor is placed directly adjacent to the laser. The finger was placed at fixed distances from the laser (1 cm, 2.5 cm, 5 cm) and then moved horizontally (left/right in Experimental Setup above). Using 19.5 K-Ohm resistor.

Note: The negative values are on the same side of the laser as the phototransistor. This results in a shorter distance for the light to travel and a greater intensity on the left side.
 

[[Image:Varying Phototransistor Position.jpg|thumb|left|300px|Click to Enlarge]]
'''Third Experiment: '''The phototransistor was moved directly out into the sheet of light (up/down in Experimental Setup). The finger was moved in same up/down direction. Using 19.5 K-Ohm resistor.
 

[[Image:Varying Phototransistor Position Horizontally.jpg|thumb|left|300px|Click to Enlarge]]
'''Fourth Experiment: '''The phototransistor was moved to the left of the laser. The finger was moved in the up/down direction. Using 19.5 K-Ohm Resistor.
 

== Limitations and Environmental Factors ==

There were a few environmental factors that affect the sensors:

1) Ambient light: The overhead light saturated the phototransistor and so the laser was pulsed (the pic was programmed to strobe the laser) in an effort to provide a noticeable difference between the ambient and laser light. As noted above, a finger in front of the transistor cast a shadow which had a larger effect (due to the blocking of the ambient light)than the actual blocking of the laser. Be aware that as the experiment is done any shadow cast on the sensors by a finger or body part will affect the ambient light sensed by the phototransistor and should be taken into account.

2) Lower resistances can be used for the phototransistor to prevent saturation but this also causes a reduced sensitivity to light.

3) The sheet laser provided was not uniform. There were different intensities of light across the line emitted.

4) There is a limited range in which the fingertip laser light sensor is accurate. Using the code and setup described above, there was accurate sensing of the fingertip directly in front of the laser and phototransistor to about seven centimeters.

5) The same finger and the fingernail side were used for all of the experiments. Results may be affected by testing with different fingers or whether it is the fingernail side or not, or a side of the finger. Instead of a finger, a white plastic dowel could be used as a control initially and then a finger used with more progress.