Electronics > Beginners

Push button power circuit for Arduino... trying to modify it for 12V input

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Ian.M:
The Arduino output may not hold its state during loss of Vcc.  If it glitches high it will re-trigger. If you've got a decent scope, look for glitches on the out pin.

If you find a glitch, try splitting the 4K7 resistor into two 2K2 ones with a cap to ground in between to make a low pass filter, with a time constant an couple of orders of magnitude longer than the glitch so it has negligible effect.

Peabody:

--- Quote from: CBF on November 19, 2021, 10:16:06 am ---I cannot get this circuit to work. It turns on correctly but when the arduino sets the output low to turn off the input floats to high. I cannot think of a solution and believe the problem is because the arduino is tri-state or my mosfet?

--- End quote ---

If you mean the GPIO pin labeled INPUT in your schematic, that should always be high unless you are pushing the button.  There's nothing pulling INPUT down.  But if you mean the power doesn't shut down, then that shouldn't be happening.  Are you keeping the output pin low for a while?  Remember that you have to recharge the gate capacitor through that 1M resistor before the mosfet will turn off.  After bringing the output low, try adding a 10 second Delay afterwards.  If that still doesn't work, instead of taking the output low, try changing it to INPUT mode, still with the Delay.



T3sl4co1l:
Just to belatedly add my own to this old thread --

I did this, with the additional constraint that it run from 24V, with low leakage.



The 24VEN goes to an LDO enable, which powers the MCU's converter (24-3.3V buck) and other hardware (12V for SMPS controllers).  This circuit draws essentially MOS leakage current until enabled, and the load's minimum current draw is still many times the bias drawn by this when on, so it's no matter at all.  It also monitors RS-232, so that serial commands can wake up the MCU directly.  Filtering not shown; ESD protection is shown.

Oh, the serial wake-up part is a bit ambiguous, isn't it... the input NMOS is wired-OR with the latching NMOS I believe?  So the right half of that is duplicating the respective part of the right hand side.  Yeah I don't have this thing in front of me right this instant to confirm, tsk tsk.

Tim

Peabody:
Just looked at the schematic again, and I think the 2.2uF gate capacitor shown in red is way too big.  Its only purpose is to prevent the circuit from powering up when power is first connected.  But for that I think .01uF or even smaller would be enough.  Try removing that cap, and then see if the circuit powers down properly.  And the 1M resistor may be too high if there's any leakage through the NPN.  Try 220K or even 100K and see if that makes a difference.  I think the circuit is sound, and should work, but you need to experiment a bit with different values.

CBF:
I tried adjusting the gate cap values and the resistor with no luck. I successfully with a different circuit. I think a low pass filter on the base of the transistor may have worked as the output did spike to negative momentarily, as Ian P suggested. Thanks anyway.

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