2008-12-20T02:44:14Z

ScottM: /* Driving and Controlling */

==Introduction==

==Types of Fans==
===Axial (Propellor)===
[[Image:AxialFanPicture.JPG |thumb|150px|right| Axial Fan]]
This type of fan uses a fixed blade that produces airflow parallel to the direction of rotation. This fan design can be seen in many cooling applications, as it is designed to maximize the volume of air moved.

===Centrifugal (radial)===
[[Image:CentrifugalFanPicture.JPG |thumb|150px|right| Centrifugal Fan]]
A centrifugal fan is constructed with an impeller inside of a rigid housing and resembles a paddle wheel. Airflow is input through the center of the impellor and is output at a single radial vent. This type of fan is designed to increase the air pressure at its output, and is used in many blowing and inflating applications

==Driving and Controlling==

==Important Practical Considerations==
===Directionality===
Most prepackaged fans are optimized to spin in a single direction. In particular, both the physical shape and orientation of the blades as well as the controller for the electric motor are designed to allow for unidirectional operation. Even if the controller may be hacked to allow for bidirectional motion, the thrust will most likely be asymmetric.

To attain true bidirectional motion, one will typically have to select a bidirectional motor and propeller blade separately (avoid prepackaged fans). R/C airplane and helicopter hobby sites typically offer good starting points for such applications.

===Phase Lag===
One of the most significant practical limitations of using a fan as an actuator is the lag when accelerating the fan. Accelerating from one velocity to another velocity (increasing/decreasing thrust) physically takes time. The amount of time is typically proportional to the difference in velocities and can be on the order of seconds.

This phase lag limitation is due to the inherent design of many prepackaged fans as they are built to provide a constant velocity with no acceleration. (They are hence actuated by a motor with a small torque) This represents a typically blowing/venting application.

The phase lag of a fan is an important consideration for applications using fans to control their motion as this will increase the complexity of the controller.

Fans As Actuators

2008-12-20T02:44:04Z

ScottM: /* Driving and Controlling */

2008-12-20T02:40:32Z

ScottM: /* Centrifugal (radial) */

Fans As Actuators

2008-12-20T02:40:17Z

ScottM: /* Axial (Propellor) */

==Introduction==

==Types of Fans==
===Axial (Propellor)===
This type of fan uses a fixed blade that produces airflow parallel to the direction of rotation. This fan design can be seen in many cooling applications, as it is designed to maximize the volume of air moved.
[[Image:AxialFanPicture.JPG |thumb|150px|center| Axial Fan]]

===Centrifugal (radial)===
A centrifugal fan is constructed with an impeller inside of a rigid housing and resembles a paddle wheel. Airflow is input through the center of the impellor and is output at a single radial vent. This type of fan is designed to increase the air pressure at its output, and is used in many blowing and inflating applications
[[Image:CentrifugalFanPicture.JPG |thumb|150px|right| Centrifugal Fan]]

==Driving and Controlling==

==Important Practical Considerations==
===Directionality===
Most prepackaged fans are optimized to spin in a single direction. In particular, both the physical shape and orientation of the blades as well as the controller for the electric motor are designed to allow for unidirectional operation. Even if the controller may be hacked to allow for bidirectional motion, the thrust will most likely be asymmetric.

To attain true bidirectional motion, one will typically have to select a bidirectional motor and propeller blade separately (avoid prepackaged fans). R/C airplane and helicopter hobby sites typically offer good starting points for such applications.

===Phase Lag===
One of the most significant practical limitations of using a fan as an actuator is the lag when accelerating the fan. Accelerating from one velocity to another velocity (increasing/decreasing thrust) physically takes time. The amount of time is typically proportional to the difference in velocities and can be on the order of seconds.

This phase lag limitation is due to the inherent design of many prepackaged fans as they are built to provide a constant velocity with no acceleration. (They are hence actuated by a motor with a small torque) This represents a typically blowing/venting application.

The phase lag of a fan is an important consideration for applications using fans to control their motion as this will increase the complexity of the controller.

2008-12-18T20:06:19Z

ScottM:

The Northwestern University mechatronics design wiki provides reference material on the theory and applications of electronics, sensors, actuators, etc., for use in mechatronics-related research and projects. Practical applications often refer to equipment and supplies available in the [http://mechatronics.mech.northwestern.edu/ Northwestern Mechatronics Design Lab].

Important: Please be sure to read the [http://mechatronics.mech.northwestern.edu/mech-rules.pdf Rules for Using the Mechatronics Design Lab].

__TOC__

<h3>Design Competition 2008</h3>

Wiki pages on sensors, actuators, programming, and microcontrollers: use pages below
<br>
* [http://www.mech.northwestern.edu/courses/433/Writeups/QuickStart/ Parts in the DC2008 quick start pack]
* [http://peshkin.mech.northwestern.edu/pic/info/piccintro_2008-01-24.pdf PIC C intro slides, as presented 2008/01/24 (pdf)]
* [http://peshkin.mech.northwestern.edu/pic/info/picinterfacing_2008-01-28.pdf PIC interfacing slides, as presented 2008/01/28 (pdf)]
<br>

<h3>Sensors and actuators for DC</h3>
* [[Using Solderless Breadboard|Solderless Breadboard & wiring that works]]
* [[Using LEDs & IREDs]]
* [[Using a laser]]
* [[Sensing optical tape|Infrared reflectivity]]
** Using phototransistors
** Sensing optical tape
* [[Comparators | Comparators : the analog digital interface]]
* [http://www.robotroom.com/FaulhaberGearmotor.html Faulhaber MiniMotor SA gearmotor with encoder], as well as [[Actuators_Available_in_the_Mechatronics_Lab#Faulhaber_1524E006S_motor_with_141:1_gearhead_and_HES164A_magnetic_quadrature_encoder|the local wiki page]]
* [[Adding a magnetic encoder to a GM3 Gearmotor]]
** Using magnetic switches (Hall Effect)
* [[High-current devices|Driving high-current devices: several options]]
* [[Driving a Stepper Motor]]
* [[Driving an RC Servo]]
* [[Accelerometers]]
* [[Strain gauges]]
* [[Using the Basic Stamp Microcontroller|Basic Stamp Microcontroller]] <b>Not recommended for DC2008</b>
* [http://www.mech.northwestern.edu/courses/433/Writeups/Battery_NiMH/ NiMH rechargable batteries and chargers]

<h3> [http://peshkin.mech.northwestern.edu/datasheets Prof. Peshkin's favorite datasheets]</h3>
<br>

<h3>PIC 18F4520 prototyping board </h3>
*[[4520 Board intro|Prototyping board intro]]
*[[4520 Board construction|Assembling the 18F4520 prototyping board, circuit, parts]]
*[[4520 Board use|Using the 18F4520 prototyping board]]
<br>

<h3>Programming with CCS C </h3>
*[[C language|The C language]]
*[[CCS C|CCS C, specifically for the 18F4520]]
*[[Embedded Programming Tips for CCS C]]
*[[CCS IDE|Using the CCS development environment]]
*[[Debugging C on a PIC]]
*[[More debugging tips]]
*[http://www.ccsinfo.com/forum/ CCS user forum]
<br>

<h3>Interfacing and skeleton code for the PIC 18F4520</h3><br>
<b>These topics have wiki pages <i>and</i> sample code available</b><br>
<b>[http://peshkin.mech.northwestern.edu/pic/code Link to all sample code here.]</b>
<br>
* [[Digital inputs & outputs]] (filename: DigitalIO)
* [[Analog Input]] (filename: AnalogInput)
** reading a trimpot
** reading a phototransistor
** amplified phototransistor, and IRED strobing
** using an instrumentation amp (example: for a strain gauge)
* [[Analog Output|Analog Output, and the I2C bus]] (filename: AnalogOutput)
* [[Waveform Generation with AD9833]] (filename: AD9833)
* [[SPI - Serial Peripheral Interface - on the PIC]]
*[[Pulse width modulation|Pulse width modulation (PWM) for driving motors or other high current devices]] (filename: MotorPWM)
** using H-bridges
* [[Interrupts]]
* [[Quadrature decoding in software]] (filename: QuadratureSoft)
* [[Quadrature decoding in hardware, or just counters]] (filename: QuadratureHard)
* [[Running RC servos]] (filename: RCservoSoft & RCservoHard)
* [[Watchdog timer]] (filename: Watchdog)
* [[PIC RS232|RS-232 serial communication between a PC and a PIC]] (filename: RS232)
* [[C Example: Serial LCD|Text output to a serial LCD display]]
* [[C Example: Parallel Interfacing with LCDs|Text output to a parallel LCD display]]
* [[Servo skeleton with fast & slow interrupts]]
* [[XBee radio communication between PICs]] (and between a PC and a PIC)
* [[I2C communication between PICs]]
* [[Serial communication with Matlab]]
* [[SPI communication between PICs]] <b> (Note: this function has not been successfully tested)</b>
* [[Microphones]]
* [[Ambient light color sensing]]
* [[Controlling a seven segment display]]
* [[Storing constant data in program memory]]
* [[PIC computation time benchmarks]]
* [[Stepper motor control with the PIC]]
* [[Global Positioning System]]
* [[IR communication between PICs]] <b> (Note: this function has not been successfully tested) </b>
* [[Interfacing to External EEPROM]]
* [[I2C Motor Controller]]
* [[Interfacing with a Photodiode Array]]

<br>
<b>These topics have sample code available, but no wiki pages yet</b><br>
<b>[http://peshkin.mech.northwestern.edu/pic/code Link to all sample code here.]</b>

* Counter0 - Counting pulses with Timer0]
* Counter1 - Counting pulses with Timer1]
* Interrupt0 - Periodic servo cycles using interrupt routines, 10mS & slower; Timer 0]
* Interrupt2 - Periodic servo cycles using interrupt routines; 10mS & faster; Timer 2]
* InterruptExternal - Interrupts generated by an external pulse]

<br>
<b>These topics need more development</b><br>
<b>[http://peshkin.mech.northwestern.edu/pic/code Link to all sample code here.]</b><br>
* AnalogOutputParallel - Analog output using 8 digital lines]
* PIC-to-PIC communication
* Zigbee radio communication
* Modulated IR communication
* Strobing LEDs or IREDs for better range and immunity to background light
* I2C communication
* CAN bus
* Capturing data to Matlab
* Running stepper motors
<br>

<h3>PIC Microcontrollers</h3>
* [[PIC Microcontrollers with CCS Compiler]], for DC, 333, etc, using the CCS ICD-U40 device <b>[this section has been replaced by the material above]</b>
* [[PIC Microcontrollers with C18 Compiler]], for e-puck, or using the Microchip ICD device or
<br>

<h3>e-puck Mobile Robot</h3>
* [[e-puck Mobile Robot]]
<br>

<h3>[[Printing Circuit Boards]]</h3>

* [[PCB Artist | PCB Artist: Software provided by Advanced Circuits]]

<h3> Electronics </h3>
* [http://hades.mech.northwestern.edu/wiki/index.php/Category:Electronics Electronics]
* [[Phase-Sensitive Detection]]
* [http://en.wikipedia.org/wiki/Operational_amplifier_applications Op-Amp Applications]
<br>

<h3>Analog and Digital chips</h3>
* [[Comparators | Comparators: the analog to digital interface]]
* [[Filtering with the LMF100 | Filtering with the LMF100]]
* [http://en.wikipedia.org/wiki/Operational_amplifier_applications Opamps : building blocks of analog computation]
* [http://www.mech.northwestern.edu/courses/433/Writeups/InstAmp/instamp.htm Instrumentation amps, and NU circuit board for them]
* [[LED Drivers | Controlling larg numbers of LEDs with LED drivers]]

<br clear=all/>

<h3>[[:Category:Sensors|Sensors]]</h3>

* [[Potentiometers|Angle, Linear Position: Potentiometers]]
* [[Optointerrupter|Beam Breaker: Optointerrupter]]
* [[Optoreflector|Proximity: Optoreflector]]
* [[Sensing optical tape|Infrared reflectivity : Sensing optical tape]]
* [[Reed Switch|Proximity: Reed Switch]]
* [[Hall Effect Sensor|Proximity, Angle: Hall Effect Sensor]]
* [[Rotary Encoder|Angle: Rotary Encoder]]
* Angular Velocity: Tachometer
* [[Photodiodes and Phototransistors|Light: Photodiodes and Phototransistors]]
* [[Photocell|Ambient Light: Photocell]]
* [[Thermistor|Temperature: Thermistor]]
* Temperature: Thermotransistor IC
* Audio: [[Microphones]]
* [[Accelerometers|Tilt, Acceleration: Accelerometers]]
* [[Strain Gauge|Force: Strain Gauge]]
* Current: Current Sense Resistor
* [[Limit Switch|Contact: Microswitch (Limit Switch)]]
* [[Ambient light color sensing]]
* [[Global Positioning System]]
* [[Optics]]
* [[Optical Locating]]
* [[Lateral-Effect Photodiode]]
* [[IR Target Illumination|IRED's]]

<br clear=all/>

<h3>[[:Category:Actuators|Actuators]]</h3>
[[image:All-actuators-captions-small.jpg|thumb|300px|[[Actuators Available in the Mechatronics Lab|Available Actuators]]|right]]

* [[Brushed DC Motor Theory|Brushed DC Motors]]
** [[Choosing a Motor and Gearing Combination|Choosing a Motor and Gearing Combination]]
** [[Linear Amplifier Motor Driver|Driving Using a Linear Amplifier]]
** [[Driving using a single MOSFET|Driving using a single MOSFET]]
** [[Pulse Width Modulation|Driving Using Pulse Width Modulation]]
** [[PIC PWM Motor Driver]]
** [[Gear Motor]]
** [[Pulse Width Modulation]]
** [[Pulse_width_modulation]]
** [[Driving using a single MOSFET | Driving a DC motor using a single MOSFET]]
** [[Driving a DC Motor using PWM]]
** [[Driving a high current DC Motor using an H-bridge]]
** [http://www.mech.northwestern.edu/courses/433/Writeups/AddEncoderHobbyEngGearMotor Adding a rotation encoder to a gearmotor]
** [[Using Opto-Isolators to Prevent Interference]]
* [[Brushless DC Motors]]
** [[Driving Brushless DC Motors]]
* [[Stepper Motor Theory|Stepper Motors]]
** [[Stepper Motor Circuits|Driving Stepper Motors]]
** [[Unipolar Stepper Motor Driver Circuit]]
** [[Bipolar Stepper Motor Driver Circuit]]
* [[RC Servo Theory|RC Servos]]
** [[555 Servo Circuit|Driving Your Servo Using a 555 Timer]]
* [[Solenoid Theory|Solenoids]]
** Practice: Driving Your Solenoid
* AC Motors
** [[Using the Yaskawa Motors]]
* Fans As Actuators
* [[Actuators Available in the Mechatronics Lab]]
<br clear=all/>

<h3>Mechanical Design</h3>
*Mechanics of Materials
**Beam Mechanics
**[[Mohr's Circle]]
*Failure Theories
**Static Loading
**Variable Loading and Fatigue
*Fastening
**Nuts and Bolts
**Keys and Keyways
**Press-fits
**Set Screws
*Support
**Housings
**Shafts
**[[Bearings]]
*Transmission
**Rigid: [[Gears]]
**Flexible: Belts, Chains
**Motion Connection/Separation: Clutches, Brakes, Couplings
*Linkages
**Serial Chains
**Parallel and Closed-Loop Chains
*Other: springs/dampers, cams, etc.

<br clear=all/>

<h3>The PC/104 Stack</h3>
[[Image:Img0174.jpg|thumb|300px|[[PC104 Overview|The PC104 Stack]]|right]]
* [[PC104 Overview|Overview]]
* [[The PC/104 Lab Kit]]
* Hardware:
** [[Advantech CPU Card]]
** [[Sensoray 526 Data Aquisition Card]]

** [http://www.mech.northwestern.edu/courses/433/Writeups/PC104BoB/stack.htm#power[Power Components]]
** [http://www.mech.northwestern.edu/courses/433/Writeups/PC104BoB/stack.htm#electrical[I/O Electronics: Analog I/O, Digital I/O, Encoder Connections]]
* Advanced: Creating a Working Stack from Parts
** [http://www.mech.northwestern.edu/courses/433/Writeups/PC104BoB/stack.htm [Building the Breakout Board]]
** [http://www.mech.northwestern.edu/courses/433/Writeups/PC104BoB/stack.htm#ribboncables[Breakout Board Ribbon Cables]]
** [http://www.mech.northwestern.edu/courses/433/Writeups/PC104BoB/stack.htm#mechanical[Assembling the PC104 Stack]]
** '''[[Creating an xPC Flash Boot Disk]]''' <- when new version of MATLAB
* Custom Boards
** Dual PWM Motor Controller
** Dual Linear Amplifier Motor Controller
<br clear=all/>

<h3>xPC Target Real-Time Operating System</h3>

* [[xPC Overview|Overview of Real-Time Programming with Simulink and xPC Target]]
* [[Configuring xPC Target PC|Configuring xPC Host/Target PC]]
* [[Creating a Simple xPC Program|'''Quickstart''':Creating a simple xPC Program]]
* [[Common xPC Blocks|Commonly Used Blocks]]
* [[Using the Host Scope]]
*Advanced
** Model Properties
** [[XPC M-file Communication|M-file communication]]
** Using outside of the lab
** [[media:standalone.pdf|Standalone Mode]]
** Stateflow
* Code Examples
** [[Controlling a DC Motor with an Encoder]]
** Something With State Machine
** [[Using RS-232 and Printing to LCD]]
**[[UDP Communications between Target and Host PC]]
** M-functions and S-functions
** [[xPC Code From Student Projects]]
<br clear=all/>

<h3>QNX Real-Time Operating System</h3>
*[[media:qnxtemplate.zip|QNX Control Program with Interrupts]]

<br clear=all/>

<h3>Lab Supplies and Data Sheets</h3>

* [http://spreadsheets.google.com/pub?key=pa_bNAhFF-OvvxpSje1KDYg&output=html&gid=0&single=true Generally stocked lab inventory ]

<br clear=all>

<h3>[[Vendors]]</h3>

<br clear=all>

<h3>Other Software</h3>
*[[List of Useful Software for Download]]
*Circuit Schematics and PCB Layout
*LaTex Document Preparation
** [http://meta.wikimedia.org/wiki/Help:Formula Mathematical Formulae]
** Document Formatting
** [[LaTeX Software Setup|Software Setup]]
** IEEE Styles

<br clear=all>

<h3>[[Other Lab Equipment]]</h3>
* Prototyping Tools
** [[Tektronix TDS220 Oscilloscope]]
** [[Tektronix CFG253 Function Generator]]
** [[media:Mastech_power_supply_manual.pdf|Mastech Power Supply]]
** Fluke III Multimeter
** Benchtop Multimeter
** Powered Breadboard
** Soldering Iron
* [http://ediacaran.mech.northwestern.edu/neuromech/index.php/Lab_Equipment High Performance Neuromechatronics Benches]
* The Sensoray 626 DAQ Card

<br clear=all>

<h3>Course Material</h3>
* [[ME 224 Experimental Engineering]]
* [http://lims.mech.northwestern.edu/~lynch/courses/ME333/2008/index.html ME 333 Introduction to Mechatronics]
** [[Lab 5]]
** [[Suggested final projects]]
** [[ME 333 final projects]]

* [http://www.mech.northwestern.edu/courses/433/ ME 433 Advanced Mechatronics]

<br clear=all>

<h3>Miscellaneous</h3>
* [[Swarm Robot Project]]
** [[Swarm Robot Project Links]]

* [[Indoor Localization System]]
* [[Robot Helicopter Project]]
* [[E-Puck Color Sensing Project]]
* [[Guitar Tunning Project]]

XBee radio communication between PICs

2008-12-18T03:52:17Z

ScottM: /* Results */

== Overview ==

Typically, two pics communicate by [http://en.wikipedia.org/wiki/RS-232 RS-232], a wired transmission. However, it may be desirable to communicate via a wireless link. This wiki page demonstrates using XBee radio modems which conform to the IEEE 802.15.4 protocol. These radios will allow for wireless communication between two PICs and between a PIC and a computer.

[[Image:XBeePinOut.jpg |thumb|300px|right| XBee Manual]]

The IEEE 802.15.4 is a [http://en.wikipedia.org/wiki/IEEE_802.15.4 point-point/point-multipoint] communications protocol (similar to Bluetooth) designed for low-power devices. Like Bluetooth, the IEEE 802.15.4 specification also uses the 2.4 GHz ISM band. The ZigBee protocol, which deals with mesh networking and routing, is built upon the IEEE 802.15.4 specification.

The XBee radios, made by Digi (formerly Maxstream), are shipped with firmware implementing the IEEE 802.15.4 protocol, but can be loaded with the ZigBee protocol stack, which can be downloaded from the Digi website. Note that ZigBee is still in its infancy and devices from different manufacturers may not be compatible. The range for an XBee Pro indoors is up to 300 feet while line of site, outdoor communication is up to a mile. ([http://ftp1.digi.com/support/documentation/manual_xb_oemrfmodules_802.15.4.pdf XBee Manual])

The XBee chip is designed to be mounted in specific sockets (Note: These sockets don't fit in a standard bread board!) We soldered wires directly to the socket, which were then placed in a breadboard. (Printed circuit boards are being created to fix this issue.) The Xbee also requires a 3.3 voltage regulator.

For the pin locations, see page 7 of [http://ftp1.digi.com/support/documentation/manual_xb_oemrfmodules_802.15.4.pdf XBee Manual] or the figure to the right.

For PIC to computer interface, a terminal program such as X-CTU needs to be used. Although other terminal programs might work as well, X-CTU software was designed specifically for the XBee, and in addition to its terminal functions, it also has functions for testing signal strength, reading, saving, and writing the state of the XBee, and updating firmware. The X-CTU program is run on the PC while connected to a X-Bee via a serial port. The X-CTU software can be downloaded from [http://www.oricomtech.com/download.htm X-CTU Site].

<br clear="all">

== Circuit ==
[[Image:pictopic.jpg |thumb|300px|left| Communicating Pic to Pic]] [[Image:pctopic.jpg |thumb|left|300px| Communicating Computer to Pic]]
<br clear="all">

The XBee module can be connected directly to the UART port on the PIC. To connect it to a RS-232 port, one must use a voltage shifting transceiver chip because RS232 signals are from -15V to + 15V. The MAX232/ST232 chip will convert voltage level from RS-232 to TTL logic levels and vice versa. The chip requires 4 external capacitors (the fifth is a bypass capacitor) in order to operate.
The transceiver data sheet can be found [http://www.tranzistoare.ro/datasheets/105/502490_DS.pdf here].

In the circuit shown above, the serial port uses a DE9F 9-pin connector (Digikey part number 209FE-ND), which is used to connect the computer's serial port to the circuit.

In order to communicate PIC to PIC, two of the circuits shown on the left should be used.

In order to communicate PIC to computer, one of each of the circuits should be used. A better solution to connecting a PC to an XBee module is to use a cable that connects to the PC's USB port and converts to RS-232, as described on this [[PIC RS232]] page.

==XBee Interface Board==
[[Image:xbee_board_with_radio.jpg|thumb|right]]
[[XBee_Interface_Board| XBee Interface Board]]

<br clear="all">

== Code ==

'''Communication PIC to Computer'''

First you will need to get your PC speaking RS-232. You can try hyperterminal (standard on the PC) or [http://homepage.mac.com/dalverson/zterm/ zterm] or similar for the Mac for simple interactive RS-232. See [[Serial communication with Matlab|this page]] for an example of RS-232 communication using matlab. Or you can try [http://www.codeproject.com/KB/system/cserialport.aspx this C++ library] from within a Win32 C++ program. In any case, you are likely to need a special adapter cable to connect your PC to the XBee as described on the [[PIC RS232]] page.

The PIC code below will wait for the character '+' to appear on the serial port, and when it does, it will add the next two single digit numbers that are entered and return the result back to the computer. In order to connect with the PIC, the program X-CTU must be used on the computer as discussed above.

<pre>
#include <18f4520.h>
#fuses HS,NOLVP,NOWDT,NOPROTECT
#use delay(clock=20000000) // 20 MHz crystal on PCB
//#use rs232(baud=19200, xmit=PIN_A0, rcv=PIN_A1) // you can use any pins for software uart...
#use rs232(baud=9600, UART1) // hardware uart much better; uses RC6/TX and RC7/RX
// characters tranmitted faster than the pic eats them will cause UART to hang.

#include <stdlib.h>

int a;
char abuff[2]={0};
int b;
char bbuff[2]={0};

char x;
int sum;

void main() {
while (TRUE) {
if (kbhit()) {
x = getc();
}
if (x=='+'){
while (!kbhit()){}
abuff[0] = getc();
a = atoi(abuff);
while (!kbhit()){}
bbuff[0] = getc();
b = atoi(bbuff);

sum = a+b;
printf("sum=%u\r\n",sum);
x=0;
}
}
}

</pre>

'''Communication PIC to PIC'''

In this communication, each PIC has its own code, which is shown below.

''Transmitter''

<pre>
/* pic2pic_transmit.c
ME333 Lab 5
The transmitter checks to see if PIN A0 is high or low.
If the pin is high, the transmitter sends the signal 'a' to the receiver and
turns on an LED. If the pins is low, the transmitter sends the signal 'b'.
*/

#include <18f4520.h>
#fuses HS,NOLVP,NOWDT,NOPROTECT
#use delay(clock=20000000) // 20 MHz crystal on PCB
//#use rs232(baud=19200, xmit=PIN_A0, rcv=PIN_A1) // you can use any pins for software uart...
#use rs232(baud=9600, UART1) // hardware uart much better; uses RC6/TX and RC7/RX
// characters tranmitted faster than the pic eats them will cause UART to hang.

#include <stdlib.h>

#define LED_0 PIN_D0

void main() {
while (TRUE) {
if (input(PIN_A0)){
output_high(LED_0);
printf("a"); //sends signal a
}
else{
output_low(LED_0);
printf("b"); //sends signal b
}

}
}
</pre>

''Receiver''
<pre>

/* pic2pic_receive
ME 333 Lab 5
The receiver checks the signal from the XBEE and if the signal is 'a', the receiver turns on an LED.
*/

#include <18f4520.h>
#fuses HS,NOLVP,NOWDT,NOPROTECT
#use delay(clock=20000000) // 20 MHz crystal on PCB
//#use rs232(baud=19200, xmit=PIN_A0, rcv=PIN_A1) // you can use any pins for software uart...
#use rs232(baud=9600, UART1) // hardware uart much better; uses RC6/TX and RC7/RX
// characters tranmitted faster than the pic eats them will cause UART to hang.

#define LED_0 PIN_D0

#include <stdlib.h>

char x;

void main() {
while (TRUE) {
if (kbhit()) {
x = getc();
}
if (x=='a'){
output_high(LED_0);

}
else{
output_low(LED_0);

}
}
}

</pre>

==Using the XBee Radio==
===Using X-CTU===
Note: Setting up the radios will require the X-CTU terminal program. Select your settings under the '''PC Settings''' tab and click on '''Test/Query'''. Unfortunately, there is no easy way to tell what the current baud rate of the radio is set at (default is 9600), so you might have to try them all. Whoever had the radio before you may have changed the settings of the radio, so after your radio is successfully detected, you may wish to use command '''ATRE''' to reset the radio to factory defaults, and '''ATWR''' to save your settings.

===Parameters AT Commands===
AT commands enable you to set the parameters of the XBee radio. To enter AT command mode, open X-CTU (program discussed in overview), make sure your radio is detected, click on the '''terminal''' tab, and type in "+++" (without the quotes). The chip should respond with an "OK". Then, you can enter the commands. If the radio doesn't receive a commands for a while (default 10s), then it will exit command mode and return to normal operation mode; you can also force a return to normal operation mode with a ATCN command. '''All parameters are in hexadecimal format.'''

Commands are usually entered in the following formats (after entering command mode):

To read parameters: AT<parameter>

To write parameters: AT<parameter> <value>

For example, to read the ID of the radio, you could enter:

+++
ATMY

To set the value of the radio's ID to 1 you could enter:

+++
ATMY 1

The radio will start using the updated parameters after exiting the command mode, or if an ATAC (apply changes) command is given. '''If you want your changes to persist after rebooting the radio, make sure you use the ATWR command).'''

'''Specific instructions and descriptions of allowable parameters to send can be found in Section 3 of the XBee Product Manual.'''

Some commonly used commands:
*+++ Enter command mode
*ATCN Exit command mode
*ATAC Apply changes
*ATWR Write current parameter values to non-volatile memory (must reset or use ATAC for changes to take effect)
*ATRE Restore defaults
*ATFR Reset
*ATCH Set channel
*ATID Set network ID
*ATDH Set desination ID (high byte)
*ATDL Set destination ID (low byte)
*ATMY Set device ID
*ATBD Set baud rate
*ATAP Set transparent/API mode

===Transparent Operation===
By default, the radios are set to work in transparent mode (as opposed to API mode).

====Unicast/Multicast Mode====
(see section 2.4.1 in the manual)

A radio will be able to send send data to any other radio having the same channel (CH parameters), PAN-ID (ID parameter), and has a source address (MY in 16-bit address mode, SL+SH parameters in 64-bit address mode; see 2.4 in the manual for more about 16-bit versus 64-bit addressing) equal to the destination address (DL parameter in 16-bit addressing mode, DL+DH in 64-bit addressing mode) of the sending radio. You can set these parameters using the AT commands.

====Broadcast Mode====
(see section 2.4.2 in the manual)

To make your XBee broadcast packets, set the DL parameters to FFFF and the DH parameter to 0.

===Proprietary API mode===
To use the API mode, set the AP parameter to 1 or 2, depending on whether you will need escape characters (see 3.4 in the manual for more information).

The API mode allows users to send data in a packet structure. Commands and specific destination addresses can be embedded into packets, which allows you to give the radio commands without having to enter the AT command mode. The packet also inclues a checksum (the packet won't be sent/received if this is wrong), and receiving packets will have things like source address and signal strength embedded.

Writing software for the API mode may be more difficult, as you have to assemble a packet and calculate a checksum. You may wish to use API mode if you need to be able to detect corrupt data or if you need to communicate to many different radios individually.

===ZigBee Mode===
Maxstream provides a ZigBee stack for the XBee, but the firmware must be changed. The firmware can be changed with X-CTU, X-CTU can uplink to a server and download the correct firmware.

==Setting up Your XBee Network==
Although the XBee radios will be able to communicate with each other straight out of the box, they will be in broadcast mode, which means that your radio will be sending data to every other radio in the room, which is in most cases undesirable. Your radio will also be transmitting in broadcast mode, which could interfere with someone else's communications.

In order for two or more XBee radios to communicate, they must
#Have the same '''channel ID'''
#Have the same '''network ID'''
#The '''source ID''' on the receiving radio must match the '''destination ID''' of the sending radio.

To set the radios for point-to-point communication, there are four things to consider:
*Source ID - The Source ID is the ID number of your particular radio. You can read or write this parameter using the AT command '''ATMY'''.
*Destination ID - The Destination ID is the ID of the radio that you want to send to.
*PAN (Personal Area Network) ID is the ID of the network. Your radio will only send to radios with the same PAN ID unless you set your own ID to 0xFFFF, which will make you broadcast across all networks on the same channel.
*Channel - This is the radio channel of your XBee radio. Radios must be on the same channel in order to communicate. You can reduce interference between different XBee networks by using a different channel.

Your radio has two source IDs:
*A unique 64-bit serial number that is set at the factory and cannot be changed.
*A 16-bit ID that you can change.

===Example: Serial Cable Replacement (2 radios)===
If you simply want a pair of radios to communicate, the best way is to use the unique 64-bit serial number of your radio, which will eliminate the problem of someone else using the same channel, PAN ID, and IDs that you are using. Configure your radios by doing the following:

For both radios,
#Set the channels to be the same.
#Set the PAN ID to be the same.
#Set DH and DL to be equal to the SH and SL of the other radio, respectively.
#Set the MY parameter to 0xFFFF. This will block any messages with a 16-bit destination address.

Example:
In this example, we set the channel, PAN ID, source ID, and destination ID. (The things that you type into the terminal are bold, the reply from the radio is plain.)

Radio1:

:'''+++'''OK<br>
:'''ATCH C'''<br>
:OK<br>
:'''ATID 3332'''<br>
:OK<br>
:'''ATSH'''<br>
:13A200 ''Note: This serial number will be unique to your hardware''<br>
:'''ATSL'''<br>
:40088B78<br>
:'''ATMY FFFF'''
:OK<br>
:'''ATWR'''<br>
:OK<br>
:'''ATCN'''<br>
:OK<br>

Now, go to your other radio.

Radio2:

:'''+++'''OK <br>
:'''ATCH C'''<br>
:OK<br>
:'''ATID 3332'''<br>
:OK<br>
:'''ATDH 13A200''' <br>
:OK <br>
:'''ATDL 4088B78''' <br>
:OK<br>
:'''ATSH'''<br>
:13A200<br>
:'''ATSL'''<br>
:40088B96<br>
:'''ATMY FFFF'''
:OK<br>
:'''ATWR'''<br>
:OK<br>
:'''ATCN'''<br>
:OK<br>

Back to Radio1:
:'''+++'''OK <br>
:'''ATDH 13A200''' <br>
:OK <br>
:'''ATDL 4088B78''' <br>
:OK<br>
:'''ATWR'''<br>
:OK<br>
:'''ATCN'''<br>
:OK<br>

==Round Trip Latency Testing==
A test measuring the round trip time of the Xbee radio was performed to gain a sense of the average latency of the XBee radios communicating over the 802.15.4 protocol.

===Experimental Setup===
One XBee radio was connected to a computer running Windows XP with a standard USB->RS232 cable. As programmed in Visual Studio C++ Express, the computer performed a "loopback" protocol; the computer wrote the data it received (to the serial port) upon the receipt of a byte (from the serial port). In this sense, the computer simply echoes the data it receives on the serial port.

A second XBee radio was connected to a PIC184520 with a 40MHz crystal. Using the PIC-C programming language, the XBee radio is controlled using the pic's hardware EUSART. A variety of baud rates were tested as listed in the table below.

To capture the round trip time, the pic was programmed to set a digital output high, and send a byte of data. Upon receipt of the data (from the loopbacked PC), the pic subsequently set the digital output low. By viewing the digital output on an oscilloscope, the width of the pulse was measured to determine the amount of time between sending and receiving a single byte of data.

*Note that the latency of the computer is included in this test. For this test, it was assumed that the latency of the computer would be insignificant relative to the radios' communication time. To remove this additional latency in the future, one should create a hardware loopback by powering the first Xbee radio and physically connecting this radio's Rx and Tx line via a wire (no computer or PIC needed).

===Results===
<table border="1" width="35%">
<tr>
<td width="17.5%">
<p><font size="-1"><b>Baud Rate (bps)</b></font></p>
</td>
<td width="17.5%">
<p><font size="-1"><b>Round Trip Latency (ms)</b></font></p>
</td>
</tr>
<tr>
<td width="17.5%">
<p><font size="-1">9600</font></p>
</td>
<td width="17.5%">
<p><font size="-1">2.2</font></p>
</td>
</tr><tr>
<td width="17.5%">
<p><font size="-1">19200</font></p>
</td>
<td width="17.5%">
<p><font size="-1">1.2</font></p>
</td>
</tr><tr>
<td width="17.5%">
<p><font size="-1">38400</font></p>
</td>
<td width="17.5%">
<p><font size="-1">1.0</font></p>
</td>
</tr><tr>
<td width="17.5%">
<p><font size="-1">57600</font></p>
</td>
<td width="17.5%">
<p><font size="-1">0.5</font></p>
</td>
</tr>
<tr>
<td width="17.5%">
<p><font size="-1">115200</font></p>
</td>
<td width="17.5%">
<p><font size="-1">0.2</font></p>
</td>
</tr>
</table>