Calibration

This example demonstrates one techinque for calibrating sensor input. The board takes sensor readings for five seconds during the startup, and tracks the highest and lowest values it gets. These sensor readings during the first five seconds of the sketch execution define the minimum and maximum of expected values for the readings taken during the loop.

Hardware Required

Arduino board
LED
analog sensor (a photoresistor will do)
10k ohm resistor
220 ohm resistor
hook-up wires
breadboard

Circuit

Analog sensor (e.g. potentiometer, light sensor) on Analog input 2. LED on Digital pin 9.

calibration

Connect an LED to digital pin 9 with a 220 ohm current limiting resistor in series. Connect a photoresistor to 5V and then to analog pin 0 with a 10K ohm resistor to ground.

Schematic

calibration sch

Code

Before the setup, you set initial values for the minimum and maximum like so:

int sensorMin = 1023;        // minimum sensor value
int sensorMax = 0;           // maximum sensor value

These may seem backwards. Initially, you set the minimum high and read for anything lower than that, saving it as the new minimum. Likewise, you set the maximum low and read for anything higher as the new maximum, like so:

// calibrate during the first five seconds
while (millis() < 5000) {
sensorValue = analogRead(sensorPin);
// record the maximum sensor value
if (sensorValue > sensorMax) {
sensorMax = sensorValue;
}
// record the minimum sensor value
if (sensorValue < sensorMin) {
sensorMin = sensorValue;
}
}

This way, any further readings you take can be mapped to the range between this minimum and maximum like so:

// apply the calibration to the sensor reading
sensorValue = map(sensorValue, sensorMin, sensorMax, 0, 255);

Here's the whole program:

Table of Contents

Calibration

Hardware Required

Circuit

Schematic

Code

See Also: