Electronic Launch controllers

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Sep 29, 2016
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I built a electronic launch controller about a year ago. Nothing fancy, but looked great and worked well.
Basically had a main switch that lit up and a led that shows its armed and ready for launch. And a launch button to fire the rocket. Basic !
Well this time around I wanted to build one with a continuity light that shows if the wires are connected and or the fuse is blown. But I can't figure out how to do it. I have followed a simple drawing and the light does not come on. Yes I checked the lamp, it works. Lol
Any help would be appreciated. ImageUploadedByRocketry Forum1475776175.012633.jpg
This is the diagram I used ImageUploadedByRocketry Forum1475776216.183792.jpgImageUploadedByRocketry Forum1475776250.524782.jpg


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Jan 19, 2009
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It's kind of hard to tell, but a couple thoughts that might help..

Is the light an LED? It might be backwards.. Make sure it has a proper current limiting resistor is it's an LED or you will blow it out.

One diagram shows a fuse and what looks to be a reverse polarity protection diode. Are those installed in your build?

When you turn on the main switch, do you get voltage from either ignitor terminal to ground (battery-)? If yes, short the ignitor clips, you should get voltage on both sides with the negative side of the meter connected to the battery ground.


Well-Known Member
Sep 1, 2010
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How long are the leads to the igniter, and what gauge wire are you using? Resistance could be too great, reducing current to below the level necessary to light the lamp...guessing it's a lamp because the symbol is one, and there's no current limiting resistor? An earlier suggestion of removing elements (igniter, fuse) in sequence and testing will help troubleshoot.


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Oct 29, 2015
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OK, I'm qualified to help.

Can you describe in more detail what you're trying to do? I'm having a hard time figuring out how the circuit is supposed to work.

You have a diode across the battery and fuse that guarantees the fuse will blow the moment you attach the battery backwards. That's OK, but may not be what you want to do.

It looks like you have a lamp (LED or Incandescent?) between the negative side of the igniter (noted as '+' in the schematic), and the ground coming off the battery. I don't see any current limiting in the circuit, so I'm going to assume that's a low-current incandescent bulb. Do you have any specs on it? If you built the launcher using the schematic as you show it, and the specs were appropriate on the bulb, the circuit should work fine.

I'll second soopirV's question, and ask where in the diagram the wire is between where you're standing and where the rocket is, and what gauge wire you're using.

You might have better luck by replacing the diode with a high-brightness RED LED and a 1 Kohm resistor, oriented so that it turns ON if the battery is connected backwards. You'll get an indication before you close the safety switch, so it'll be good. Then I'd remove the lamp, and replace it with a 1K Ohm resistor and a high brightness GREEN led, oriented so that it turns on when an igniter is attached. With my suggested changes, you'll get a good GREEN light when the igniter is attached, and you'll only be putting 10 ma through the igniter - which means it won't accidentally ignite just from the current going through it and the light.
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