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driving a tri-color LED via separate 12v earth and 12v supply Answered

Hi Peeps,

I'm currently (pun intended) building a motorbike and want to have minimum clutter on the bike. I am wanting to incorporate a tri-colour LED to indicate status for high beam lamp AND neutral indicator lamp. If both are active, it will indicate Amber(or yellow).

so the problem is, high beam is easy to acheive as its a 12v supply, neutral is more complicated as this operates pysically via earth on the gear change. I need some sort of relay to drive a 12v supply, but have very limited space to do it in.

do you guys have any suggestions?

I'm looking at a height of 10mm max and length 20mm so transistors or something. I can solder and follow a circuit board so any suggestions what to do would be appreciated.

Thanks peeps

7 Replies

AndyGadgetBest Answer (author)2011-03-13

Here's a (very) rough sketch of what you need. It would be an idea to put a 0.1uF capacitor directly across each LED as well to give some protection from transients. I'm assuming you've got a common cathode LED. You'd need to swap things around a bit for common anode.

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AndyGadget (author)AndyGadget2011-03-13

I've just re-read the size constraint and that is pretty tight. Do a search for '12v subminiature relay' and you may find something that small. THIS one nearly does it.
If there's nothing suitable this could be done with a transistor, but relays are more resilient in an automotive environment like this.
p.s My sketch doesn't show the bi-colour LED too well but that is meant to be the two LEDS in the device.

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drewpi (author)AndyGadget2011-03-13

Cheers AG

that looks good, how resilient are the minature relays? this is a twin cyl bike and there is vibration (but I could isolate the vibes with closed cell foam)

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AndyGadget (author)drewpi2011-03-13

I was thinking electrically resilient rather than mechanically.
As long as the 'bike has suspension relays will be fine.

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lemonie (author)2011-03-13

If you have a 2-colour LED the logic table is:
OFF ON = RED (e.g.)
ON OFF = GREEN (e.g.)
ON ON = GREEN & RED which appears yellow as the 3rd colour.

Connect the two indicator lamp supplies to 2 of the LED pins and the other to GND.


(use resistors, be sure the bike's power supply is well regulated)

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drewpi (author)lemonie2011-03-13

thanks for the info on this, it helps me get my head round the issue

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