Using the Sharp IR Sensor to detect objects and their distance

Arduino → Arduino Tutorials and Guided Projects → VEX + Arduino, Mobile Robotics Platform → Using the Sharp IR Sensor to detect objects and their distance

Configuration

Now that we know how the sensor works and have it wired up, it is time to program it in ROBOTC. First we need to tell ROBOTC how the robot is configured.

In addition to the servos, you should configure analog pin 0 as an analog sensor, and call it sharpIR.

Your configuration code should now look like this:

#pragma config(CircuitBoardType, typeCktBoardUNO) #pragma config(UART_Usage, UART0, uartSystemCommPort, baudRate200000, IOPins, dgtl1, dgtl0) #pragma config(Sensor, anlg0, sharpIR, sensorAnalog) #pragma config(Motor, servo_10, rightServo, tmotorServoContinuousRotation, openLoop, IOPins, dgtl10, None) #pragma config(Motor, motor_11, leftServo, tmotorServoContinuousRotation, openLoop, reversed, IOPins, dgtl11, None) //*!!Code automatically generated by 'ROBOTC' configuration wizard  !!*//

Reading the Sensor

To get the reading from the sensor, you use "SesnorValue[]" just like with any other sensor. The Sharp IR sensor:

• returns lower values for object at further distances
• returns higher values for object that are closer.

Since the returned value does not have a linear relation to the distance, you can use the following formula and/or table to find the exact distance if needed.

D = distance in mm

V = the measured value

ADC Value	Voltage (V)	Distance (mm)	Distance (cm)	Distance (in)
80	0.391	841	84	33.1
120	0.586	518	52	20.4
160	0.781	367	37	14.4
200	0.977	280	28	11
240	1.172	225	23	8.9
280	1.367	187	19	7.4
320	1.563	160	16	6.3
360	1.758	139	14	5.5
400	1.953	122	12	4.8
440	2.148	109	11	4.3
480	2.344	98	10	3.9
520	2.539	89	9	3.5
560	2.734	82	8	3.2
600	2.93	75	8	3
640	3.125	69	7	2.7
680	3.32	65	6	2.5

Distance (mm) Distance (cm) ADC Value Voltage (V) 800 80 84 0.41 750 75 88 0.43 700 70 93 0.454 650 65 99 0.483 600 60 106 0.518 550 55 114 0.557 500 50 124 0.605 450 45 135 0.659 400 40 149 0.728 350 35 166 0.811 300 30 189 0.923 250 25 220 1.074 200 20 265 1.294 150 15 337 1.646 100 10 472 2.305

Distance (in) ADC Value Voltage (V) 32 82 0.4 30 87 0.425 28 92 0.449 26 98 0.479 24 105 0.513 22 113 0.552 20 122 0.596 18 133 0.649 16 147 0.718 14 164 0.801 12 187 0.913 10 217 1.06 8 262 1.279 6 333 1.626 4 466 2.275

Making the Program

To make it easier, and since we want the same result, we will be modifying an existing program to use the Sharp IR sensor. We will start with the code for the VEX ultrasonic rangefinder.

task main() { while (true) { //Make sure the value is not an error if(SensorValue[ultrasonic] > 0) { if (SensorValue[ultrasonic] <= 7) { //there is something within the threshold range motor[leftServo] = -50; motor[rightServo] = 50; wait1Msec(800); } else { //nothing in the threshold range motor[leftServo] = 50; motor[rightServo] = 50; } } } }

Since the Sharp IR sensor also returns a range of values, all we really need to do is change any reference of the ultrasonic sensor to reference the Sharp IR sensor instead. We will also need to adjust the threshold by using the lookup table mentioned earlier. Remember to change the config code!

#pragma config(CircuitBoardType, typeCktBoardUNO) #pragma config(UART_Usage, UART0, uartSystemCommPort, baudRate200000, IOPins, dgtl1, dgtl0) #pragma config(Sensor, anlg0, sharpIR, sensorAnalog) #pragma config(Motor, servo_10, rightServo, tmotorServoContinuousRotation, openLoop, IOPins, dgtl10, None) #pragma config(Motor, motor_11, leftServo, tmotorServoContinuousRotation, openLoop, reversed, IOPins, dgtl11, None) //*!!Code automatically generated by 'ROBOTC' configuration wizard  !!*// task main() { while (true) { if (SensorValue[sharpIR] >= 230) { //there is something within the threshold range motor[leftServo] = -15; motor[rightServo] = 15; wait1Msec(400); } else { //nothing in the threshold range motor[leftServo] = 15; motor[rightServo] = 15; } } }