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I am trying to design a push button that turns my device on upon a single press and turns it off upon holding the push button for a few seconds.

I found this circuit:

Circuit diagram

Aside from the 10uF capacitor and the 300k resistor which are used as a RC time delay for the press and hold to turn off effect, what do the rest of the components i.e. the 10k, both 100k resistors and the 1uF and 0.1uF capacitors do?

Also, my device runs on 3V3 power so I'm not sure if it will still work with these component values, which is why I'm asking the above question.

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1 Answer 1

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First of all 3.3V should be enough since that MOSFET has a very low gate threshold. You would maybe touch up some resistor but in principle it should work as-is.

The 'series' capacitors are used to transform a level into an edge, as differentiators. When you change polarity they briefly conduct while changing charge and that's developed in a potential by the associated resistors.

The other 100k resistors are simply pullup to hold the lines to a definite state since MOSFET are, essentially, open circuits when seen from the gate. Also, they develop the capacitor pulses.

I presume the auto-on/off switch chooses the state when you power on the circuit, the 100nF capacitor in that case gives the inital pulse.

Of course the top MOSFET runs the load while the bottom one latches the gate of the top one, if it wasn't clear. Hope it helps

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  • \$\begingroup\$ I'm encountering this problem where the on latch is working but the off latch is not. I'm using everything as it is, but on a 3.3V power as mentioned previously. Why is it that after turning it off, it will turn back on automatically? \$\endgroup\$ Apr 23, 2021 at 6:59

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