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simplest circuit that doesn't work

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rudytj

New Member
i am trying to simply get a LED to light up when i turn on an air compressor in my jeep. I drew up a simple diagram of the circuit, i left out the fuse and the pressure switch as they have no bearing on the circuit that i can see. The led is connected the correct way, has the resister built in (from radio shack) and is not blown (still works if i don't put it in the circuit). but it does not turn on when i switch the compressor on. I am feeling like the kid in "breakfast club" whose lamp wouldn't light up when he pulled the trunk...don't make me get a flare gun!!!!



scott
 
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giftiger_wunsch

New Member
From your diagram, it appears you've most likely blown out the LED. What's the rating on the LED? It should have a series resistor, as most LEDs will be destroyed as soon as they are connected directly to a battery like that... sorry, I just realised it's a car battery. As far as I'm aware, virtually any LED will be destroyed by a car battery supply :eek:
 
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rudytj

New Member
thank you...i just edited the original post to explain that it has the resistor for 12v (radioshack) built in and it still works not in the circuit

scott
 

giftiger_wunsch

New Member
I'm assuming the rest of the circuit works, i.e. there isn't a problem with the battery? Perhaps the part is faulty. Try checking the voltage across the LED / current through the LED with a multimeter while connected and switched on.

Sorry, just realised you said it works in a different circuit. Either way, try testing the current through the LED with it switched on. If you don't detect a current, try checking the connections...
 
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rudytj

New Member
i can check for the voltage across the LED later, the rest works as planned flip switch...compressor clutch locks up and the compressor pumps untill the pressure switch turns it off at 100psi. i tried multiple ground points for the LED.
 
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giftiger_wunsch

New Member
Well your descriptions seem to suggest that the battery works, the switch works, the LED works, and it's correctly wired. Make sure your physical circuit matches the basic diagram you posted, check the connections, and double-check each component works...
 

rudytj

New Member
so you agree it should work...i'll put the flare gun away and look for operator error.

I just wanted to make sure it wasn't more complicated like the resistor causing to much resistance. or that the compressor clutch was drawing to much etc

scott
 

kpatz

New Member
Aside from the obvious (checking the connections), verify that the switch is on the +12 side of the circuit and not the ground side, otherwise you'd get zero volts to the LED. Also, make sure the polarity on the LED is correct. Check the voltage too, maybe the compressor draws a lot of current and there's some resistance that's causing a voltage drop, though I would think the compressor would run poorly in that instance.
 
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audioguru

Well-Known Member
Most Helpful Member
The schematic was posted over at PhotoBucket but now it is gone.
Why not post the schematic here??
 
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