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Make an RGB LED show different colours based on range finder distance
Use a ping sensor to determine distance and then depending on the distance,
show warmer or cooler colours.
Built using a ping))) Sensor and connected to a RGB display.
Uses the ping))) example in the base Arduino install, written by David Mellis & Tom Igoe
#define PING_PIN 7
#define RED 9
#define GREEN 10
#define BLUE 11
#define BLUE_LONG 400
#define BLUE_SHORT 175
#define GREEN_LONG 225
#define GREEN_SHORT 75
#define RED_LONG 125
#define RED_SHORT 0
void setup() {
// initialize serial communication:
// set the LED off
pinMode(RED, OUTPUT);
pinMode(BLUE, OUTPUT);
// uses a common anode RGB LED (so +5v turns them off)
digitalWrite(RED, HIGH);
digitalWrite(GREEN, HIGH);
digitalWrite(BLUE, HIGH);
void loop()
long distance;
distance = ping();
// now depending on the distances we map the colours on the LED.
// BLUE will be bright at about 350 cm fading out to 175cm
// GREEN will be bright about 225cm fading out to about 75cm
// RED will be faded at about 125cm getting bright to 0cm
if (distance > RED_LONG) {
digitalWrite(RED, HIGH);
} else {
analogWrite(RED, map(distance, RED_LONG, RED_SHORT, 255, 0));
if ((distance > GREEN_LONG) || (distance < GREEN_SHORT)) {
digitalWrite(GREEN, HIGH);
} else {
analogWrite(GREEN, map(distance, GREEN_LONG, GREEN_SHORT, 255, 0));
if ((distance > BLUE_LONG) || (distance < BLUE_SHORT)) {
digitalWrite(BLUE, HIGH);
} else {
analogWrite(BLUE, map(distance, BLUE_LONG, BLUE_SHORT, 255, 0));
long ping() {
// returns the distance to the nearest object.
// establish variables for duration of the ping,
// and the distance result in inches and centimeters:
long duration, cm;
// The PING))) is triggered by a HIGH pulse of 2 or more microseconds.
// Give a short LOW pulse beforehand to ensure a clean HIGH pulse:
digitalWrite(PING_PIN, LOW);
digitalWrite(PING_PIN, HIGH);
digitalWrite(PING_PIN, LOW);
// The same pin is used to read the signal from the PING))): a HIGH
// pulse whose duration is the time (in microseconds) from the sending
// of the ping to the reception of its echo off of an object.
duration = pulseIn(PING_PIN, HIGH);
// convert the time into a distance
return (microsecondsToCentimeters(duration));
long microsecondsToCentimeters(long microseconds)
// The speed of sound is 340 m/s or 29 microseconds per centimeter.
// The ping travels out and back, so to find the distance of the
// object we take half of the distance travelled.
return microseconds / 29 / 2;

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ajfisher commented Jul 2, 2011

This circuit assumes a Common Anode RGB LED. Wire up ANODE to +5V and the other connections to your PWM pins which must be driven LOW to turn the LED on. Driving PWM pins HIGH will turn the LED off.

Wire up an ultrasonic sensor to a digital input pin on the Arduino. Code for this is based on ping))) from Parallax and uses the public domain code written by David Mellis, edited by Tom Igoe.


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cdastan commented Aug 20, 2014

Hi there AJ, thanks for the code! I'm wondering how to change the code to work with a common cathode RGB LED. Is it a simple change from "digitalWrite(RED, HIGH);" to "digitalWrite(RED, LOW);" for each color? I have tried this and it doesn't seem to be working correctly so I am asking why and how other parts of the codes may require editing based on drawing from ground as opposed to +5V.


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paolajuvenal commented Jun 24, 2015

hi AJ! your code is great, we are trying to turn off the other 2 colors of light when the distance is at the specific color! can you help, pleaseeeeeeeeee!

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