# plane full of LEDs

• posted

I had decided to go with 12 volts running sets of 3 LEDs with 68 ohm resistors, but then I found an old transmitter battery and an old receiver battery lying around in my basement. I thought it would be a lot easier to put them together without splitting the receiver pack in half, so I ended up making a 12 cell battery. I also dug through a little drawer full of loose resistors that I happen to have, and I found a handful of 33 ohm and a handful of 39 ohm. These will run sets of four LEDs in series, as confirmed by a test that I did last night.

The great thing about using my mismatched bulk supply of resistors is that when the battery is running down, half of the LEDs will go out before the other half. As I recall, this was also the case on my friend's airplane that inspired me to do this project. He said that this was very useful because he never had his lights go out unexpectedly while flying.

• posted

I have had that happen a couple of times. Once when a short unexpectedly ran the battery flat rather suddenly and once when the on/off switch was being cycled by a faulty servo. Exciting times that are well avoided. The first case I managed to make a landing by moonlight and the spectators could not see the airplane. The second case I set the power to idle, flaps down, and prayed.

• posted

Just a few things - did you ever work out what the forward voltage is of your LEDs? I think people assumed it was 3.5v, but do you know for sure? It's easy to find out using a multimeter if the data isn't available.

Secondly, as I'm sure you realise, a 12 cell battery is not 12v, rather, more like 15v.

• posted

They are rated 3.0 to 3.8 volts, 25 mA. I wanted to make a 12 volt battery at first, but I ended up making a 14.4 volt battery because it was easier.

• posted

You might like to measure the voltage across just one of the LEDs in the chain - that'll confirm the forward voltage. You could also measure the voltage across the resistor - divide that voltage by the value of the resistor (I=V/R) and you can confirm what current they're running at.

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