Help with a launch controller...

So here's what i have...an electronic key on/off switch, an LED and a momentary button trying to wire to a battery pack. I would like the light to work like a continuity light where I turn the key and it's ready to launch it lights up. I just have no idea how to wire it and I don't understand wiring diagrams.

These look like Radio Shack parts. Do you know the part numbers? This is kinda important, because LEDs typically run on only 3 volts, and require a current limiting resistor so they won't burn out if used with higher voltages. Radio Shack sells some that already have this part wired inside, with the correct value, to be used at 12 volts.

276-0270

WaltG said:

276-0270

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OK, good. That part is the LED with a correct current limiting resistor. You'll need to power the controller from a 12 volt battery.

A basic controller circuit is pretty simple. You need paired wire like speaker wire (or so-called "zip" cord). You can tell the two wire apart because one will either be a different color, or have a stripe or ribs running down it. Pick one wire (one color, or one with/without stripes-ribs) and don't mix the two. Because you're using an LED, polarity is important.

The way the circuit works is that one wire runs straight from the battery to the rocket (through the box). The switches and LED go on the other wire. Let's put the switches on the positive (+) wire. The circuit has two switches. The key switch turns the power on/off. The push switch goes across the LED and shorts it out so that all of the power goes to the engine "starter".



pay attention that the red wire from the LED is connected to the power switch (which goes to the + side of the battery).

circuit redrawn:



Not shown are clips for the battery or engine starter.

What my controller looks like:


let me know if you need more help.

Awesome. Thank you. For now using wires that came with kit. Went to launch for my son and nothing happened. Snipped wires and connected directly to battery and zoom...lol

Of course that launch had its problems

I did find something helpful. Michaels craft stores always has a 40-50% coupon you can print and has a few rocket things including large packs of engines

Ok. Don't know how well you can see this but I hope I got it right.

Looks like you got it right. Testing it will let you know for sure!

Well this seems stupid but didn't want to waste an igniter to hooked up to old pc fan I I think it's a winner. Light should be on when I turn key on and off when I push button?

Yeah, kinda. The way it works is that the LED (and resister) allow just a little current to pass through the engine "starter", but not enough to set it off. If there is a complete circuit, the LED will lite. When you press the push switch, you short across the LED and all the power from the battery goes to the "starter" (I *really* hate using that term!). Your test with the fan shows that everything is wired up in correct polarity. I'm betting it will work.

Now just gotta get a new rocket since old one stuck in tree....lol

WaltG said:

Now just gotta get a new rocket since old one stuck in tree....lol

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Can't help you with that one!

Should there be a resistor on here somewhere? If so where and which one?

WaltG said:

Should there be a resistor on here somewhere? If so where and which one?

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If this is your part



then it already has a 680 ohm resistor in it.

In your fan test you hooked up the fan and turned the key switch on, right ? LED lit but fan didn't spin until you pressed the button, correct ? You've built a two-switch parallel circuit. The path through the LED has (or should have) a higher resistence to current flow than the path through the momentary switch. Connecting the clips and turning the key completes the higher resistence path with enough juice flowing to light the LED but not enough to activate the device at the end of the clips. Pushing the button activates the second path and those electrons take the path of least resistance; the light goes out and whatever is at the end of the clips gets more amps. I might go ahead and sacrifice an igniter for complete peace of mind.

Someone was asking about resistor so wanted to be safe

WaltG said:

Should there be a resistor on here somewhere? If so where and which one?

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I posted something about that then deleted the post when I realized the spec for the led was 12v/20ma. I'm used to working with leds that are 3.3v rated and that requires an additional resistor to bring the voltage [12v] and current down. Being rated at 12v it should only pass the 20ma listed. However it is also a good idea to check that with a VOM just in case :y: happens.


Richard

Tested and worked great. Need to test on a rocket now. Thanks for all you're help. Next gonna try to make my own ignitors. Local radio shack going out of business so might get some 5-10 ohm resistors and do something with that.

So I got some 1/4 watt 10 ohm resistors. They heat up and smoke. If I attached a match to it would it be enough to ignite it?

So I got some 1/4 watt 10 ohm resistors. They heat up and smoke. If I attached a match to it would it be enough to ignite it?

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Yes it will. The 1/8 watt,10 ohm resistors work faster though. That's what I use for my igniters dipped in a liquid pyrogen.

Steve G

1/8W resistors are better as they can take less current to overload them. But they're still going to be fairly large. Miking your own igniters using fine gauge nichrome (and pyrogen dip) is better, as you can fabricate them to be small enough for even BP motors.

Well launch controller worked like a charm. Took the kids out for 3 launches today. No problems.