How to Use RGB LEDs to Identify Colours - DIY Colour Sensor
by TechMartian in Circuits > Sensors
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How to Use RGB LEDs to Identify Colours - DIY Colour Sensor
![WwnCKXzmRoC3eX+jObuJqQ_thumb_7a9.jpg](/proxy/?url=https://content.instructables.com/FQN/K6PA/J6QQJ5UD/FQNK6PAJ6QQJ5UD.jpg&filename=WwnCKXzmRoC3eX+jObuJqQ_thumb_7a9.jpg)
![RGB LED Colour Detector](/proxy/?url=https://content.instructables.com/FIC/3DBN/J6IF481P/FIC3DBNJ6IF481P.jpg&filename=RGB LED Colour Detector)
This is a DIY colour detector made only using an RGB LED and a photoresistor sensor.
I got a comment and request from one of my Instructables that they would like to see an LED used as a colour detector. Then, I got the idea that if I were to use an RGB LED, I can detect all the colour spectrum possible by sending PWM signals to the LED.
BoM
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- Arduino
- RGB LED
- Photoresistor
- 10kΩ resistor
- 3x 100Ω Resistor
- Jumper
- Breadboard wires
Wire the RGB LED
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This will be the emitter part of our circuit emitting different colours which will bounce off of objects, by the law of optics which will be detected by our photosensor.
* Connect pin 2, the longest pin to the GND pin on the Arduino.
* Connect pin 1, the red coloured LED of the RGB LED to pin 5 on the Arduino.
* Connect pin 3, the greed coloured LED of the RGB LED to pin 6 on the Arduino.
* Connect pin 4, the bleu coloured LED of the RGB LED to pin 9 on the Arduino.
You will notice that all of these are plugged into PWM pins marked with a tilda symbol "~" so that we can independently control the brightness of each of the LEDs.
Wire the Photosensor
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The reflected light from the emitter (RGB) LED bouncing back off of any objects will be read by the photosensor which will used calibrated values to find the individual R-G-B colour values of a particular colour.
Make sure you move the photosensor very close to the emitter.
* Connect one of the pins, call this pin 1, of the photosensor to the GND pin on the Arduino
* Connect pin 2 of the photosensor to the 3.3V pin on the Arduino.
* Connect pin 2 of the photosensor to the A0 pin on the Arduino.
You will notice that the last two wirings are all parallel. This is because we are making a voltage divider to get the changing voltage reading as the reflected light changes in intensity.
Code
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![Screen Shot 2017-08-25 at 10.58.35 AM.png](/proxy/?url=https://content.instructables.com/FMH/S2SM/J6QQJ5WC/FMHS2SMJ6QQJ5WC.png&filename=Screen Shot 2017-08-25 at 10.58.35 AM.png)
![Screen Shot 2017-08-25 at 10.58.43 AM.png](/proxy/?url=https://content.instructables.com/FTW/BD38/J6QQJ5WD/FTWBD38J6QQJ5WD.png&filename=Screen Shot 2017-08-25 at 10.58.43 AM.png)
// Define colour sensor LED pins
int ledArray[] = {5,6,9};
// boolean to know if the balance has been set boolean balanceSet = false;
//place holders for colour detected int red = 0; int green = 0; int blue = 0;
//floats to hold colour arrays float colourArray[] = {0,0,0}; float whiteArray[] = {0,0,0}; float blackArray[] = {0,0,0};
//place holder for average int avgRead;
void setup(){ //setup the outputs for the colour sensor pinMode(2,OUTPUT); pinMode(3,OUTPUT); pinMode(4,OUTPUT); //begin serial communication Serial.begin(9600);
} void loop(){
checkBalance(); checkColour(); printColour(); } void checkBalance(){ //check if the balance has been set, if not, set it if(balanceSet == false){ setBalance(); } } void setBalance(){ //set white balance delay(5000); //delay for five seconds, this gives us time to get a white sample in front of our sensor //scan the white sample. //go through each light, get a reading, set the base reading for each colour red, green, and blue to the white array for(int i = 0;i<=2;i++){ digitalWrite(ledArray[i],HIGH); delay(100); getReading(5); //number is the number of scans to take for average, this whole function is redundant, one reading works just as well. whiteArray[i] = avgRead; digitalWrite(ledArray[i],LOW); delay(100); } //done scanning white, now it will pulse blue to tell you that it is time for the black (or grey) sample. //set black balance delay(5000); //wait for five seconds so we can position our black sample //go ahead and scan, sets the colour values for red, green, and blue when exposed to black for(int i = 0;i<=2;i++){ digitalWrite(ledArray[i],HIGH); delay(100); getReading(5); blackArray[i] = avgRead; //blackArray[i] = analogRead(2); digitalWrite(ledArray[i],LOW); delay(100); } //set boolean value so we know that balance is set balanceSet = true; delay(5000); //delay another 5 seconds to let us catch up }
void checkColour(){ for(int i = 0;i<=2;i++){ digitalWrite(ledArray[i],HIGH); //turn or the LED, red, green or blue depending which iteration delay(100); //delay to allow CdS to stabalize, they are slow getReading(5); //take a reading however many times colourArray[i] = avgRead; //set the current colour in the array to the average reading float greyDiff = whiteArray[i] - blackArray[i]; //the highest possible return minus the lowest returns the area for values in between colourArray[i] = (colourArray[i] - blackArray[i])/(greyDiff)*255; //the reading returned minus the lowest value divided by the possible range multiplied by 255 will give us a value roughly between 0-255 representing the value for the current reflectivity(for the colour it is exposed to) of what is being scanned digitalWrite(ledArray[i],LOW); //turn off the current LED delay(100); } } void getReading(int times){ int reading; int tally=0; //take the reading however many times was requested and add them up for(int i = 0;i < times;i++){ reading = analogRead(0); tally = reading + tally; delay(10); } //calculate the average and set it avgRead = (tally)/times; } //prints the colour in the colour array, in the next step, we will send this to processing to see how good the sensor works. void printColour(){ Serial.print("R = "); Serial.println(int(colourArray[0])); Serial.print("G = "); Serial.println(int(colourArray[1])); Serial.print("B = "); Serial.println(int(colourArray[2])); //delay(2000); }
Calibrate
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First prepare a black and white piece of paper before the uploading the code.
After uploading the code, you will notice that during the first 5 seconds of the program running the RGB LED will emit a variety of colours. Place a black paper over the LED and photosensor for this first 5 seconds. Then switch the paper to the white piece of paper for the next 5 seconds.
The code is written so that these first 10 seconds are the calibration period.
Test and Enjoy!
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Take different coloured paper and test it out. It will print the individual R, G, B values onto the screen.