Controlling the intensity of LED's

lil_fairee

Controlling the intensity of LED's

in Integration and Hardware • 2 years ago

Hi,

Im very new to processing so I'm looking for a little bit of help. At the moment Im making an RGB LED change color by turning on the desired color and the others off, depending on a value given to it. However what I need to do is have different variations of the each colors intensity as I have more than just three values. This just is an example of the simplistic method that Im using with some of the values:

if (temp == 17)

{

arduino.digitalWrite(ledPinR, Arduino.HIGH);

arduino.digitalWrite(ledPinG, Arduino.LOW);

arduino.digitalWrite(ledPinB, Arduino.LOW);

}

if (temp == 16)

{

arduino.digitalWrite(ledPinR, Arduino.LOW);

arduino.digitalWrite(ledPinG, Arduino.HIGH);

arduino.digitalWrite(ledPinB, Arduino.LOW);

}

If I have a value of 15 I would still like the green LED to light but at a lower intensity than 16.
Any help would be greatly appreciated and I apologize for asking what is probably a very basic question.

Replies(5)

23132421

Re: Controlling the intensity of LED's

2 years ago

Well, at the moment you're using a digitalWrite, so you have two values: HIGH, or LOW.

If you want something in-between, you're going to have to use an analogWrite and a pwm pin on your arduino.

lil_fairee

Re: Re: Controlling the intensity of LED's

2 years ago

Thanks for the quick reply! Care to elaborate a little?

if (temp == 17)

{

arduino.analogWrite (ledPinR, (temp*25));

arduino.digitalWrite(ledPinG, Arduino.LOW);

arduino.digitalWrite(ledPinB, Arduino.LOW);

}

Something like this? Cant seem to get it to work. The pins Im using are 9 10 and 11.

23132421

Re: Controlling the intensity of LED's

2 years ago

Apologies if you know this already: PWM refers to Pulse width modulation. Basically, it means that you are affecting the number of pulses of electricity that are being sent to the LED. The electricity that flows to the LED does not flow in a steady stream, it flows in a series of pulses too quick for your eye to catch (to put it another way, your LED is flickering really really fast).

PWM changes the number of pulses to dim the light (I believe its a value between 1-255?).

I haven't done arduino stuff for a while, but this page from the arduino site seems to indicate that you need to do something like arduino.analogWrite(ledPinR, 150);.

Finally, there are only a few pins on your arduino that accept PWM. They should be labeled as such.

Again, I'm rusty on this, but I think (?) it's correct.

Jesse Sco..

Re: Controlling the intensity of LED's

2 years ago

That's correct.

You can either setup variables for high, medium, low (or however many steps you want) eg.

int high = 255;

int med = 155;

int low = 55;

and then pass those values like

if(temp == 17) {

arduino.analogWrite(ledPinR, med);

arduino.analogWrite(ledPinG, low);

arduino.analogWrite(ledPinB, low);

}

... or you could use the map() function

int high = map(temp, 0, 17, 0, 255);

...

lil_fairee

Re: Re: Controlling the intensity of LED's

2 years ago

Thanks so much for your help. However when i try to incorporate the analog write into my sketch the LED will not light up any more as it did with digital write, and I cant see what the problem is.

import processing.serial.*;
import cc.arduino.*;
import processing.xml.*;
int temp;
int loopcheck = 5000;

Arduino arduino;
int ledPinR = 9;
int ledPinG = 10;
int ledPinB = 11;

void setup()
{

println(Arduino.list());
arduino = new Arduino(this, Arduino.list()[0], 57600);
arduino.pinMode(ledPinB, Arduino.OUTPUT);
arduino.pinMode(ledPinR, Arduino.OUTPUT);
arduino.pinMode(ledPinG, Arduino.OUTPUT);

}

void draw()
{
String urlCork = "http://weather.yahooapis.com/forecastrss?p=EIXX0011&u=c";
XMLElement report = new XMLElement(this, urlCork);
println(report.getChild("channel").getChild("item").getChild("yweather:condition").getIntAttribute("temp") + "°C in Cork today");
temp = int(report.getChild("channel").getChild("item").getChild("yweather:condition").getIntAttribute("temp"));
println(temp);
delay(loopcheck);

int high = 255;
int med = 155;
int low = 55;

if (temp < 20)

{

arduino.analogWrite(ledPinR, high);

arduino.analogWrite(ledPinG, low);

arduino.analogWrite(ledPinB, low);

}

}

I know that todays temperature is below 20 degrees so shouldn't it be lighting?

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