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Soft circuit trouble? Answered

I am having trouble with a project that I am working on.  I have 12 leds in parallel spiraling out from a centre connected by conductive thread, the Led's are yellow and where stripped from a battery powered led xmas light set.  I intend to use the battery holder and on/off switch unit that came with it (2X1.5v batteries and has a 6.8ohm resister) to power the lights.  Unfortunately when I connect the power supply to the lights the first led is bright and it each led following is progressively less bright, the leds at the end are pretty dim. 

So this is basically the same circuit that the xmas lights had but with conductive thread instead of wire.  I double checked that there were no loose or crossed threads.  After discovering the problem I checked the details about the conductive thread and it has a resistance of 30ohms/foot.  The length of the thread connecting all of the leds is roughly 1ft. 

So I'm guessing the problem is that there is too much resistance in the circuit? Or is there something else I'm doing wrong?

Is there any way that I can change this circuit so that it can still run on 3v batteries (2x1.5v)? 



Best Answer 8 years ago

Yep, at a guess that sounds like resistance.

Simplest fix: Make sure the wires to each LED are roughly the same length. If you've wired it as a spiral, replace that with a star configuration, with positive and negative stars all converging at a central point. You might need some "wasted" length zigzagging back and forth to make it come out evenly, especially for the LED(s) near the center.

Another fix would be to add resistors to the brighter resistors to dim them down until they're even with the dimmer ones, then increase the voltage to compensate.


Answer 8 years ago

Thanks for your response, I like your first suggestion of having the wires the same length, in my spiral the further out the leds are the large the gap is between them. I am just having a little trouble visualizing how a star configuration would look like, and were the wires would run, would you be able to show me a diagram?


Answer 8 years ago

+ wire from battery runs to a central point. Equal-length wires run from that point to each LED's + terminal. - wire from battery runs to another central point; equal-length wires from _that_ point run to each LED's - terminal.


8 years ago

I did a search on conductive thread and from what I am seeing its biggest use is for adapting gloves to be able to use touch screens on phones and such. So I think the problem is that they are not designed to transfer much in the way of current. They do enough so they can register a touch but not power anything.
If you want to stick with using the thread to connect your lights you need to make it more conductive. You can do that by adding a thin copper wire, wrapping it around the thread in a spiral. You can get the ideal wire for this by getting a cheap extension cord and striping the insulation off and using one of the fine strands of wire inside. The wire can conduct more than enough to run the lights and its very flexible so it can work with the thread. Its also fairly strong. Its one downfall might be if it flexes a lot over time it might break.
Its very handy wire and pretty cheap, you might find you can use it in a lot of ways.


Answer 8 years ago

Thanks, I will to try this, orksecurity's suggestion helped a bit but the lights are still a bit dim.