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You're right, parallel and a protection diode is always a good shout.

I'll still be going CAN-BUS route as i'd like mine to function with the M button, not the power button as i tend to drive everywhere with the power button on, but then press M mode when i want to have some fun.
 

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It depends on the resistance of the sport button LED. Either would really work. You CAN wire it paralell, but remember electricity favors the path of least resistance. My thought was a relay coil with ~10Ω or likely less of resistance will win vs. an LED which typically has high resistance since an LED internally is essentialy an air gap that curent flows over which produces the light.
 

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It will work but id get something with lugs or socket unless you are putting on a pcb and in a box

Parralell will work, series will halve the voltage and probably wont operate your relay and dim the led

Dont forget a diode or relay with inbuilt led, that will also stop the voltage spike when the coils field collapses
 

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reviving an old thread: has anyone succesfully implemented the idea to drive a relay off the Power button status LED circuit- If so, any hints, tips, limitations? For example, is it known definitively to work if you run a relay off the circuit in parallel with the LED, or in series, and is an additional protection diode required.
 

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reviving an old thread: has anyone succesfully implemented the idea to drive a relay off the Power button status LED circuit- If so, any hints, tips, limitations? For example, is it known definitively to work if you run a relay off the circuit in parallel with the LED, or in series, and is an additional protection diode required.
Here is an idea..... Why not use an optocoupler to drive the relay, you might need a fet it's way to early for solid design now, but that way you get complete isolation and protection for the dme and the draw on it is less.
 

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Here is an idea..... Why not use an optocoupler to drive the relay, you might need a fet it's way to early for solid design now, but that way you get complete isolation and protection for the dme and the draw on it is less.
A very good suggestion - it certainly would negate any issues or concerns about the back emf of the relay damaging the DME.
That being said, it kinda defeats the purpose of the Power button idea of a simple solution. If going through that much effort I think I would rather go the Arduino/Can Bus/M-Button route, which adds programability. Though I have no experience with Arduino...
 
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Beniki
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