We have tried to test and calibrate the distance sensor (SHARP 2Y0A21) using Arduino. Based on the lab test of a specific detector, the sensor data is noisy sometimes and only works for distance from 5 cm to 40 cm. We added a filter using median data of readings. And, we convert the readings to actual distance by using a quadratic regression curve fit. The test result is not perfect but acceptable. The Arduino code is attached below./********************************************************************
Blinking two LED repeatly for visual effect.
Measuring distance using SHARP 2YOA21 IR distance detector.
Based on the lab test, the distance detector works between 5-40 cm.
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// pin 10 & pin 13 have LEDs connected.
int led1 = 13;
int led2 = 10;
// pin A2 has an distance detector connected.
int IRSensor = A2;
// number of readings used to smooth the sensor data.
const int numReadings = 5;
// distance detector readings array
int readings[numReadings];
// distance array for comparison
int IRState[numReadings];
// median of the "numReadings" distance detector readings
int IRMedian;
int i, j;
int tmp;
int distance;
// the setup routine runs once when you press reset:
void setup() {
// initialize the digital pin as an output.
pinMode(led1, OUTPUT);
pinMode(led2, OUTPUT);
// initialize serial communication at 9600 bits per second:
Serial.begin(9600);
// make the IRSensor's pin an input:
pinMode(IRSensor, INPUT);
// initialize arrays
for (i = 0; i < numReadings; i++)
{
readings[i] = 650;
IRState[i] = 650;
}
}
// the loop routine runs over and over again forever:
void loop() {
digitalWrite(led1, HIGH); // turn the LED on (HIGH is the voltage level)
digitalWrite(led2, LOW); // turn the LED on (HIGH is the voltage level)
delay(20); // wait for 0.02 second
digitalWrite(led1, LOW); // turn the LED off by making the voltage LOW
digitalWrite(led2, HIGH); // turn the LED off by making the voltage LOW
delay(20); // wait for 0.02 second
// read the input pin and put the value at the end of the readings array:
for (i = 0; i < numReadings - 1; i++)
readings[i] = readings[i+1];
readings[numReadings - 1] = 650 - analogRead(IRSensor);
// copy readings array to IRState array for comparison
for (i = 0; i < numReadings; i++)
IRState[i] = readings[i];
// bubble sort IRState array
for (i = 0; i < numReadings - 1; i++)
for (j = i+1; j < numReadings; j++)
if(IRState[i] <= IRState[j])
{
tmp = IRState[i];
IRState[i] = IRState[j];
IRState[j] = tmp;
}
// find median
IRMedian = IRState[numReadings/2];
// converting the sensor readings to distance through a quadratic regression curve fit
distance = 0.000162059 * (float) IRMedian * (float) IRMedian - 0.0290382 * (float) IRMedian + 7.17082;
// Print out the distance on serial port
Serial.println(distance);
delay(1); // delay in between reads for stability
}
