12V lights instead of status LED's

I want to use old 12V lights as status indicators instead of suggested LED’s.
What I found in the manual is dat the status connections pull to ground when active, am I right about this?
After some research I found that I should connect the 12v light with a P-channel MOSFET to be controlled with the 3.3v from the board. I’ve been doing some test but i can’t seem to get it working.

Any suggestions here?

Can you add more information about what you tried and the result ?

Try this.

N Channel

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Thank you for this, awesome!
Do you have an idea on what MOSFET and Transistor to use? I’m not really into the names and numbers of those yet…


Any general purpose NPN transistor will do e.g BC184, BC337 and for the the N-channel FET e.g. 2N7002. Vgs on switch on is about 10V so find a FET with this in mind. if you’re just switching an LED, use a 1K2 resistor. This will limit the LED current to 10mA (12/1200) = 10mA


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Thanks a lot Stewart.
I will have to order the FET and transistor, I’ll give an update when i’m able to test that setup.

Had a little succes trying with some parts I had laying around, a BC337 and P16nf06 FET.
The 12v flashes a bit when the LED on the board flashes. However it doesn’t turn off all the way when the LED is off. Is this a matter of trying different resistors?

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Looks good, can make a lamp with music inside :slight_smile:

Excellent. Can you scope the gate voltage when its switching?

A super simple circuit is to use an OptoDarlington such as a TIL 197. It’s a 4 pin chip so all you need to do is to take the LED output from the board and feed it via a suitable resistor into Pins 1 & 2 (which is essentially an LED) then attach Pin 3 to the lamp supply ground and pin 4 to the lamp negative and the lamp positive to the +12 supply. The chips also come in a 2 way and 4 way package - TIL 198 & TIL 199.

This has the advantage of completely isolating your Arylic board from the lamp circuit so could reduce potential supply interference from the 12v side.

PC817, PC827 or PC847 optocouplers with transistor outputs may be better suited as I don’t know the spec of the lamps you have but they are pin to pin compatible with the TIL197 types. If you need more power then these optocouplers will replace the transistor stage in stewc’s circuit quite nicely and give the benefit of isolation.

ULN2803A is a also a pretty useful chip for these applications but are not opto-isolated and you may need to invert the logic going in with some NOT gates but again, very simple to use.

This is awesome, thank you very much! This is actually kind of what i’m looking for.
What i’ve found in my region to try is LTV-847, would that also work?
Having 4 channels is perfect.

LTV-847 Datasheet

This is the light I will be using.

@stewc I’ve been very busy these days so didn’t get to test the previous setup and check the gate voltage. I’ll try to do that the coming days.

I like to use TLP592AF-ND. The only external component you need is a 330 ohm resistor on the input of the Opto led. These also provide isolation from the 12v.