issue hooking up multiple infrared emitters

Forum 2005-2010 (read only) Hardware Troubleshooting
1

Once again, I admit to my arduino newbiness...but I'm working on a project that would involve 5 infrared emitters connected to my arduino pins. I can get one up and running fine at normal operating voltage (1.5V - 1.7V) by connecting it to pin 13, but when I try to connect the other emitters to pins 12, 11, etc, they only get 1.2V. I've tried almost every resistor I could think/dream up. I've even tried connecting directly and relying on the internal resistors...any way I put it I'm only getting 1.1V - 1.3V and the emitters don't put out enough light to register properly on my receivers. Is there something stupid I'm missing? Thank you!

OS: Windows XP Pro
Model: Arduino Duemilanove
Chip: ATMEGA168

2

You should be able to drive those IR emitters from any of the Arduino's digital I/O pins. You will need a resistor for each of them (apart from pin 13). Could you post the sketch code that you've used? Remember to put a 'pinMode' function call in your 'setup' function, to set the pins to act as outputs. What resistor values did you use?

3

I've tried multiple resistors, but as it stands now, I've got a 33Ohm resistor from pin 12 to the emitter. I have all of the pin modes set as output as well. When I measure the V off of the resistor it reads 1.17V. The particular emitter that I'm using gives of a visible red light, but even with 1.17V it's not visible.

I've slimmed down the code so all it should be doing is turning on the emitters connected to pins 13 and 12. Nothing special...here's the code:

int ledPin1 = 13;
int ledPin2 = 12;

void setup()
{
  pinMode(ledPin1, OUTPUT);
  pinMode(ledPin2, OUTPUT);
}

void loop()
{
  digitalWrite(ledPin1, HIGH);
  digitalWrite(ledPin2, HIGH);
}
4

When I measure the V off of the resistor it reads 1.17V.

I don't quite understand what you mean by that. If you connect a voltmeter to the Arduino I/O pin (positive) and Ground (negative), you should read 5V. Then, if you move the positive lead of the meter to the junction of resistor and LED, you should read the LED's forward voltage of 1.7V or so.

If you want to measure the LED current, then you'll need to select a current (Amps) range and put the meter in series with the LED.

33 Ohms sounds a little low, but with IR emitters, you need quite high current, so it may be OK. I would expect nearer 150 Ohms or 220 Ohms for an ordinary red LED.

5

All good advice above but this caught my eye:-

the emitters don't put out enough light to register properly on my receivers

Some receivers really on the IR light being modulated at a certain frequency (normally about 32kHz). They are designed to reject continuous light. That might be your problem.

6

It looks like part of my problem may be just this. I was able to get steady readings after switching around the receivers...it appears that they truly are matched pairs. I'm just using standard Radio Shack stuff. Now I guess it's up to me to straighten things out.

Thanks!

7

. . . and the ol' trick about looking at your IR led through the viewfinder of a digital camera may help.

BTW in your sample code you can move what you have in loop() into setup() and accomplish the same thing.