After searching online for an answer to how to convert a toggle switch to a momentary switch I found the circuit below. I've simulated it and it works in CircuitLab.


simulate this circuit – Schematic created using CircuitLab

I'd like to do the same thing using a transistor instead of a relay but so far I haven't been able to make it work in CircuitLab. Can I convert a toggle switch to momentary switch using a transistor and capacitor?


I believe something like this would work for you:

You will have to play around with the cap and resistor values in order to achieve your desired timing and intensity for the lamp.

  • 2
    \$\begingroup\$ I would also add a diode between the base of the transistor and ground (cathode to base, anode to ground) to deal with the negative going edge (-12V) when the capacitor is switched to ground \$\endgroup\$ – JIm Dearden Jun 22 '13 at 6:48

Note that the behaviour of these two circuits is not equivalent. The first circuit will be active on both transitions, while the second will be active on low to high, but not on high to low (or won't work at all without that diode).


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