Infrared LED question

Forum 2005-2010 (read only) Hardware Interfacing
1

Hi,

I'm trying to make an infrared emitter-detector circuit using this infrared LED: http://www.vishay.com/docs/81002/81002.pdf

The detector part of the circuit definitely works (it responds to my TV remote control) but I can't pick up anything from this IR LED...

The wavelengths of the 2 components are matched so I think it should work in theory, which means I must be doing something wrong with the LED...

I thought it would just require a resistor to ground (like a normal LED)...

Any help/suggestions would be much appreciated!

2

The datasheet says 12 deg as the half angle, in other words it is a very narrow beam. As you cant see the IR you may simply not be pointing the IR LED at the detector right. ?

It is possible you may have a boroken/damaged one, you could measure that you still have th e1.6V forward voltage drop when passing 20mA through it.

3

Most digital cameras are sensitive to IR; you could use one to see if your LED is lighting (don't use the optical viewfinder of a DSLR!)

4

I'm trying to make an infrared emitter-detector circuit using this infrared LED

That is only an emitter what are you using for the detector?
Does the detector use modulated light? All IR remotes use modulated light.
If so then you need to modulate the IR diode at the same frequency as the detector expects.

5

Modulate the IR diode

... in this context means that it can't just be "on". It has to be going on/off/on/off so rapidly that when viewed with an IR sensive webcam or video camera, or digital camera with screen, not optical viewfinder... it seems, to a human to be "just on".

The speed at which it is going on/off/on/off matters too.

Point that TV remote at whatever webcam, etc, you have avialable. If you can see the IR from the remote, you SHOULD see the IR from your LED...

6

Thanks for the webcam tip; it seems to confirm that there is definitely nothing coming out of my IR LED, as it detects my TV remote fine...

In answer to somebody's question, the detector I'm using is http://www.vishay.com/docs/81508/81508.pdf - it too picks up the TV remote so I assume it works fine.

I've tried lots of different IR LEDs so it's not a faulty component... can't think what I'm doing wrong!

7

can't think what I'm doing wrong!

Well as you aren't telling us what you did do it is hard for us as well.

It could be you have the diode the wrong way round or have not defined the pin it is connected to as an output.

8

Sorry about that, I thought I'd made it clear in my earlier post. The LED is connected between the 5V pin and ground through a resistor (I've tried a range of values...), and is definitely connected the right way round as this circuit works fine with a normal LED.

9

have you tried using another infrared led? you may have burned yours out

10

Yes I've tried several of the IR LEDs, as well as a couple of different ones...