making a simple LED light

[Force Flow]

I've got a little project in the works here, and was trying to make an infrared LED light.

Now, I'm not very good with electronics past some of the fundamental basics of electricity, but here's what I have:

Two LR41 button batteries, rated at 1.5V (from what I can tell).

A red LED. This plus the two button batteries works in a little keychain light I had, so I figured I could do the same thing, except with an infrared light. Apparently not.

I got an infrared LED found at radioshack. I don't understand the significance of all these when it comes to figuring out what is needed in terms of power and resistors, but here's what was on the back of the box:

electrical characteristics:
forward voltage: 1.2V
forward current: 100mA

absolute maximum ratings:
forward voltage (20mA): 1.6V
reverse voltage: 5V
forward current: 1.2A
reverse current: 10uA


So, what I've tried is first both button batteries, then only a single button battery. Neither worked (I was viewing the IR LED through a digital camera, since it picked up the light from a TV remote).

Any ideas? I've never had much luck with this stuff, so hopefully I didn't blow the IR LED.

[Brad the best]

i would try a AA or something along those lines . little more amperage out of it . hooking it up the right way?

[Lespaul20]

I would try reversing the way you are hooking it up. LED are diodes so they only allow current to flow one way.

[Force Flow]

Yeah, had it the right way.

The AA did work, with the red LED, but dimly. So I tried it with the IR LED, which worked, but dimly.

So, I tried it with the button batteries again. As it turns out, this *did* work. Because of the lighting conditions and moving the LED around, I just couldn't actually see that it was turning on with the camera.

Thanks guys :)

[sgtspector]

Try connecting the leads from the led to the terminals on a 9-volt battery. That will light the led just fine. An expert in the filed once told me that it works just fine. I've been meaning to try it for a while now myself but never got around to it. A couple placed in a room and you could light a whole room up for your video camera. If you look directly at it you will see a tiny red dot from the led if it is lit.

[glc]

9 volts exceeds the rating of that LED, it will blow it out.

[The_YongGrand]

Put a resistor on it - a 9V will fry the LED! :eek:

[sgtspector]

Perhaps they used a different led but I was told that you could simply connect the led to the battery and it would work. But like I said I never did get to test it.

[Force Flow]

To a 9V? No.

[Brad the best]

ya a 9v wouldn't work the problem is amperage not voltage .aa has more amperage then a watch battery .

[liambl]

You could try connecting two AA batteries in parallel to increase current.

[David M]

Borrow a DC power supply, the type where you can control the voltage and the current. Set the current at the diodes rated current. Start out low and slowly bring up the voltage until until it works. Make sure you have the polarity correct. You will then be able to use a battery and a potentiometer to provide the correct voltage. Make sure the battery has at least the same or more current capacity than the diodes rating (amperage). Use a good multimeter for measuring the voltage across the diode...so you know what the voltage is supposed to be by experimentation.

[helicopter]

ForceFlow:
I am new to the forum and this is post #2 for me.
Here is the help you need with LED's:
http://ledcalc.com/

You need a bias resistor with this circuit. Any voltage from a battery
can used to calc the correct resistor! So Easy a cave....

Peace!
Helicopter

[Petef56]

Try this...

Use the two 1.5v batts in series so you have a 3v source.
Then use a 15 ohm 1/4 watt resistor in series with the LED.

or...

Use a 9V batt.
Then use a 75 ohm 1 watt resistor in series with the LED.

---pete---

[Force Flow]

hmm...could've sworn I replied to this and closed this issue...


Oh well...In any case, the wiring I had wasn't making good contact, but other than that, I was able to make it work with the parts I had

Thanks guys :)