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There's been a lot of soft-latched power switch circuits discussed here and elsewhere on the internet. However, I can't wrap my head around how to implement the following requirements:

  • Battery powered (Lipo voltage range, LDO is used for noise reasons, device will measure in the millivolt range)
  • Push to turn on (short hold to turn on would be acceptable too)
  • While on, register button presses from MCU to handle soft power off
  • Way for MCU to power system off
  • Hold to force system off in case micro hangs

That last point is rather important as this circuit will go into a device where it would be very inconvenient/impossible for the user to disconnect the battery.

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  • 1
    \$\begingroup\$ use a microcontroller to handle the button functions \$\endgroup\$ – jsotola Feb 11 at 7:27
  • \$\begingroup\$ PIC10(L)F320/322 \$\endgroup\$ – jonk Feb 11 at 7:35
  • \$\begingroup\$ Pinhole access to microswitch is used on Lenovo laptops. \$\endgroup\$ – Transistor Feb 11 at 7:40
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You can use a latch circuit and MCU together to work out solution on your own.

  1. Once, button is pressed, the MCU will be powered
  2. MCU will ASAP latch the power latch (Power Enable, for example ) circuit, keeping the Power supply ON.
  3. Any further button press will be detected my MCU as interrupts
  4. If ti is along press, MCU can detect that too.
    In case it is needed to isolate the MCU, a timer circuit or a RC delay can be triggered to bypass the MCU latch thereby cutting the power for the whole board.

One of the dedicated IC example: Search for On - OFF controllers.

enter image description here

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  • \$\begingroup\$ Point 4 is what I'm struggling with right now. I need the user to be able to turn off the device even when the MCU decides not to cooperate. \$\endgroup\$ – Crazor Feb 11 at 9:12
  • \$\begingroup\$ BTW, I like the SRC0 chip. So far, I only managed to find chips that are either >5 bucks in small Q or have a MOQ of hundreds or thousands \$\endgroup\$ – Crazor Feb 11 at 9:15
  • \$\begingroup\$ electronics.stackexchange.com/questions/68223/transistor-delay getting a delay of couple of seconds.. the cuiruicts are plausible.. you can come up with simple logic to AND the two conditions, output of this delay circuit and MCU.. My suggestion is to break down the solutions into blocks are work on individual blocks \$\endgroup\$ – User323693 Feb 11 at 9:25

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