Need help with a battery powered IR LED Array

Thread Starter

Jumper

Joined Nov 25, 2009
16
Well... I hate to back down from a challenge, but I am a n00b. I'm not a complete n00b but anything I do from here with this project would require a lot of help from you (SGT Wookie) or the forum and I fear my avalanche of questions would get old... And with my application I (think) can tolerate quite a range of light output from the declining voltage of a discharging battery. Just as long as both arrays have exactly the same output. I'm going to test the simple version that I have and probably build the low-voltage detection circuit posted by TKNG211 and add it later if the array works like I think it will. I appreciate all the help so far Sgt Wookie but I think I'll have to pass on your challenge.

I've got my array soldered together, I'm just working on the wiring now.
 

Thread Starter

Jumper

Joined Nov 25, 2009
16
Update:

Well I have achieved success thanks to the help I've received here! I had to make 2 sets of arrays actually since the first one didn't work for me. It lit up and didn't release the magic smoke (cool term I learned here :) ) but it did not work for its intended use.

I ended up making 2 identical arrays that used 21 IR LED's each. I wasn't sure what light intensity I would need so I used a 27Ω resistor and a 1K pot for each string of 7 LED's. The pot's would allow me to exactly balance the light output of the LED's which was very important because I couldn't tolerate any spots of uneven intensity in my arrays. Everything had to be equal. I also tested my LED's as Sgt Wookie suggested to get rid of those that were grossly out of tolerance. Here's a couple pics of the arrays. Its a comically simple circuit for the genius's here which made it a good starter circuit for me.





 

Thread Starter

Jumper

Joined Nov 25, 2009
16
This is what it looks like in the dark. Camera is a Sony Nightshot video camera:



The array shines down on an optical sensor that senses the shadow of an object as it passes by. In my case the application is a ballistic chronograph that calculates the speed of a bullet as it passes across the two screens. Unequal light on the sensors causes errant readings.

I think I'm going to make another set and use 940nm IR LED's with a 50 degree dispersion. The current LED's are 880nm and I wanted it to work with an IR filter over the sensor. The IR filter theoretically would filter out ambient light making it more sensitive. But for whatever reason it did not work with the filter over the sensor. The next version will have some bells and whistles. A battery life indicator maybe... Maybe a type of light sensor I could place at the sensor that would measure the light intensity at each sensor to make sure they are equal... Lots of fun in my future. Thanks again for all the help.
 
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