Ultrasonic ranging - Revision history

Lynch: /* Overview */

2009-02-16T08:11:43Z

Overview

Lynch at 08:11, 16 February 2009

2009-02-16T08:11:18Z

Ben Tollberg: /* Circuit */

2009-02-12T05:47:02Z

Circuit

Ben Tollberg: /* Circuit */

2009-02-12T05:46:39Z

Circuit

Ben Tollberg: /* Overview */

2009-02-12T05:45:36Z

Overview

Ben Tollberg: /* Circuit */

2009-02-12T05:45:16Z

Circuit

Ben Tollberg: /* Overview */

2009-02-12T05:44:37Z

Overview

Ankur Bakshi: /* Code */

2009-02-12T05:17:04Z

Code

Ankur Bakshi: /* Code */

2009-02-12T05:16:02Z

Code

Ankur Bakshi: /* Code */

2009-02-12T04:36:39Z

Code

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 [[Image:Ultrasonic_Ranging.JPG|right|thumb|400px|]]
-The Ping Ultrasonic Distance Sensor by Parallax has three pins. These pins are +5V, I/O, and Ground. In order to activate the sensor, a 5 microsecond 5V signal must be sent to the I/0 pin. The sensor then waits 750 microseconds before sending an ultrasonic wave. The sensor sets the I/O pin to high (+5V). When the sensor receives the reflected ultrasonic wave, it sets the I/O pin to low. The time that the I/O pin is high represents twice the distance of the object, as the wave must travel to the object and be reflected back. The sensor is rated for 2cm to 3m, though it will measure distances as far as 3.47m. After the sensor has received a signal there is a 200 microsecond refractory period. Due to the delay and the refractory period, one must wait 19.455 milliseconds between successive measurements (18.5 milliseconds to measure 3m + 5 microseconds to active the sensor + 750 microsecond delay + 200 microsecond refractory period). Charts diagramming the effects of elevation and angle of the object relative to the sensors can be found in the product documentation ([https://www.parallax.com/Portals/0/Downloads/docs/prod/acc/28015-PING-v1.5.pdf]).
+The Ping Ultrasonic Distance Sensor by Parallax has three pins. These pins are +5V, I/O, and Ground. In order to activate the sensor, a 5 microsecond 5V signal must be sent to the I/O pin. The sensor then waits 750 microseconds before sending an ultrasonic wave. The sensor sets the I/O pin to high (+5V). When the sensor receives the reflected ultrasonic wave, it sets the I/O pin to low. The time that the I/O pin is high represents twice the distance of the object, as the wave must travel to the object and be reflected back. The sensor is rated for 2cm to 3m, though it will measure distances as far as 3.47m. After the sensor has received a signal there is a 200 microsecond refractory period. Due to the delay and the refractory period, one must wait 19.455 milliseconds between successive measurements (18.5 milliseconds to measure 3m + 5 microseconds to active the sensor + 750 microsecond delay + 200 microsecond refractory period). Charts diagramming the effects of elevation and angle of the object relative to the sensors can be found in the product documentation ([https://www.parallax.com/Portals/0/Downloads/docs/prod/acc/28015-PING-v1.5.pdf]).
 <br><br><br><br>

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-== Original Assignment ==
-In this project you will demonstrate that you can measure distances using an ultrasonic transmitter and receiver, at distances up to a few meters.  While you could build from components (see, for example, [http://www.micro-examples.com/public/microex-navig/doc/090-ultrasonic-ranger.html this website]), in this project you will use [https://www.parallax.com/Store/Sensors/ObjectDetection/tabid/176/CategoryID/51/List/0/Level/a/ProductID/92/Default.aspx?SortField=ProductName%2cProductName this pre-packaged PING))) ultrasonic sensor].  Your results can be displayed on an LCD screen (see, e.g., [[C Example: Serial LCD]] or [[C Example: Parallel Interfacing with LCDs]]) or on a PC using the USB/RS-232 cable (see [[PIC RS232]]).
 == Overview ==

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 In the circuit, the black wire represents ground. Pin C5 was used as the output pin responsible for activating the sensor. The external triggers RB0 and RB1 were used to identify when the I/O pin of the sensor was set to high and low respectively. Pin C6 is used for RS-232 communication to the PC. In order to setup LCD output, see [[C Example: Parallel Interfacing with LCDs]].
-<br><br><br><br><br><br><br><br><br><br><br><br>
+<br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br>
 == Code ==

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 In the circuit, the black wire represents ground. Pin C5 was used as the output pin responsible for activating the sensor. The external triggers RB0 and RB1 were used to identify when the I/O pin of the sensor was set to high and low respectively. Pin C6 is used for RS-232 communication to the PC. In order to setup LCD output, see [[C Example: Parallel Interfacing with LCDs]].
+<br><br><br><br><br><br><br><br><br><br><br><br>
 == Code ==

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 The Ping Ultrasonic Distance Sensor by Parallax has three pins. These pins are +5V, I/O, and Ground. In order to activate the sensor, a 5 microsecond 5V signal must be sent to the I/0 pin. The sensor then waits 750 microseconds before sending an ultrasonic wave. The sensor sets the I/O pin to high (+5V). When the sensor receives the reflected ultrasonic wave, it sets the I/O pin to low. The time that the I/O pin is high represents twice the distance of the object, as the wave must travel to the object and be reflected back. The sensor is rated for 2cm to 3m, though it will measure distances as far as 3.47m. After the sensor has received a signal there is a 200 microsecond refractory period. Due to the delay and the refractory period, one must wait 19.455 milliseconds between successive measurements (18.5 milliseconds to measure 3m + 5 microseconds to active the sensor + 750 microsecond delay + 200 microsecond refractory period). Charts diagramming the effects of elevation and angle of the object relative to the sensors can be found in the product documentation ([https://www.parallax.com/Portals/0/Downloads/docs/prod/acc/28015-PING-v1.5.pdf]).
+<br><br><br><br>
 == Circuit ==

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        printf("%f meters\n",distance);
     }
  }

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 == Code ==
+Setup RS 232 support with appropriate baud rate and UART support.
  #include <18f4520.h>
  #fuses HS,NOLVP,NOWDT,NOPROTECT
  #use delay(clock=40000000)
- #use rs232(baud=19200, UART1) // hardware UART; uses  RC6/TX and RC7/RX
+ #use rs232(baud=19200, UART1)
+Global variables for the timer and the distance.
  int16 timer;
  float distance;
+This interrupt will be activated when external trigger RB0 transitions from Low to High. This function will initialize Timer 1 to 0.
+ #INT_EXT
- #INT_EXT             // designates that this is the routine to call when pin RB0/INTO changes state
  void INT0isr() {
-    SET_TIMER1(0);    // initialize timer 1 to 0
+    SET_TIMER1(0);
  }
+This interrupt will be activated when external trigger RB1 transitions from High to Low. This function will retrieve the time from Timer 1. It will then calculate the distance of the object. The .0000004 term represents the .8 microsecond increment of Timer 1 divided by 2. Division by 2 is required since the wave must travel twice the distance that is being measured. The speed of sound is estimated as 343 m/s at room temperature. If there is a temperature sensor, the speed of sound can be calculated as follows: <math>Csound=331.5+(.6*TCelsius)</math>. The if statement is used to prevent the detection of the activation signal.
- #INT_EXT1             // designates that this is the routine to call when pin RB1/INT1 changes state
+ #INT_EXT1
  void INT1isr() {
-    timer=GET_TIMER1(); // records timer 1 value
+    timer=GET_TIMER1();
-    distance=timer*.0000004*343; //scale timer
+    distance=timer*.0000004*343;
-    //.0000004 = .8 microsecond increment of the timer divided by 2
-    //Dividing by 2 is necessary because the time the wave takes to return to the sensor is twice the distance
-    //343 is an approximation for the speed of sound (in m/s) at Room Temperature, a temperature sensor could be
-    //used to estimate the speed of sound using the formula V=331.5+(.6*TCelsius)
     if(distance >.01) {
-       printf("%f meters\n",distance); //print out the Value in meters
+       printf("%f meters\n",distance);
     }
-    //this if statement is designed to ignore the initial signal used to activate the sensor
  }
  void main() {
+Enable the interrupts on pin RB0 and RB1
     enable_interrupts(INT_EXT);
     enable_interrupts(INT_EXT1);
     enable_interrupts(GLOBAL);
-    ext_int_edge(0, L_TO_H);      // interrupt on INT0/RB0 pin, low to high transition
+    ext_int_edge(0, L_TO_H);
-    ext_int_edge(1, H_TO_L);      // interrupt on INT1/RB1 pin, high to low transition
+    ext_int_edge(1, H_TO_L);
-    setup_timer_1(T1_INTERNAL|T1_DIV_BY_8); // start timer T1, which counts in .8 microsecond increments
+Initialize Timer 1. Timer 1 will count in .8 microsecond increments.
+    setup_timer_1(T1_INTERNAL|T1_DIV_BY_8);
+This loop will continue continuously measure the distance of an object.
     while(true) {
-       output_high(PIN_C5); //send signal to Ultrasonic Sensor for 5 microseconds
+A 5 microsecond signal activates the sensor.
+       output_high(PIN_C5);
        delay_us(5);
        output_low(PIN_C5);
-       input(PIN_C5); // set pin to input, since the sensor has one pin for I/O, pin c5 can not be outputting a signal
+The PIC pin must be set to an input to permit the sensor pin to send a signal.
-       delay_ms(200); //changeable delay
+       input(PIN_C5);
+A delay is added since there is a refractory period for the sensor. This delay can be changed to as low as 19.5 milliseconds.
+       delay_ms(200);
     }
  }