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By Mee_n_Mac
#147281
hassmaschine wrote:but I'd be supplying the LEDs with 5v, not 12v?
Ahhh, now I understand. At one point I thought you weren't sure the cluster had enough 5V "umpf" left to run the LEDs and so were going to run them off 12V.
I intend on using the 12v to switch the transistor on? will that not fly?
It should fly just fine.
By hassmaschine
#147339
okay, I've got the circuit built and it works! yay! :)

question - it appears I get some current leakage from the 12v source. If I disconnect 5v and switch the transistor on, it still powers the backlights (albiet dimly). That means I should increase R2, correct?

I built a new board with the op-amp for the gas gauge, and thought it didn't work. then I realized I switched which pin was ground on my 20 pin header, so it wasn't connected. woops. :oops:
By Mee_n_Mac
#147345
hassmaschine wrote:okay, I've got the circuit built and it works! yay! :)
question - it appears I get some current leakage from the 12v source. If I disconnect 5v and switch the transistor on, it still powers the backlights (albiet dimly). That means I should increase R2, correct?
Hmmmm. If you've disconnected 5V from the system and still get the LEDs to come on, it means there's another source of current for the LEDs someplace in the cluster, no doubt some indirect path through some "high" resistance. The value of R2 shouldn't make any difference. If you increase it enough to stop any light output, it won't work when the 5V to the LEDs is present. There's no way the 12V is going through the transistor to turn on the LEDs. Something is not quite the way we think it is. Is it possible the cluster has another "driver circuit", in parallel with the transistor you've added, and that's somehow suppling power to the LEDs ??
By hassmaschine
#147365
perhaps - to be clear, it only turns them on when I activate the transistor, they don't stay on. and when I hook up the 5v, they appear to work normally.

I'm not seeing anything that looks like it's getting overheated, so maybe I won't worry about it too much.