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I would like to make a circuit that turns on a power supply to a microcontroller after holding down a button for a period of time (say 2 seconds). To make matters slightly more complicated, if possible, I would like to use this button as an input also. The power off could come from another switch if need be.

I was thinking of something like a latching RC circuit to an zener that switches a MOSFET on to allow power through. Ideally the solution would not consume power until the switch is pressed.

Thanks for any help

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  • \$\begingroup\$ Why not just delay the code running in your microcontroller by 2 seconds? Unless this is a power related thing. Some of the power sequencing devices are expensive. You can build your own using a small micro. \$\endgroup\$ – Gustavo Litovsky Mar 22 '15 at 21:06
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You may want to search for "power supply sequencers" and "powerpath controllers" at Linear Technology, Maxim and TI. Those devices integrate a variety of sequencing and control functions including on/off, delay start, sequencing of multiple supplies. Some have integrated FETs.

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How about using a tiny 6-pin MCU like the PIC10F200? That's the sort of application they were designed for.

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  • 2
    \$\begingroup\$ ...I have always wanted to play with those little things. \$\endgroup\$ – Kellenjb Jul 26 '10 at 12:35
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Maybe you could use the switch to connect power to the MCU, then have a timing loop there that waits for the two seconds and if it's still running, it'll turn on a FET (or other pass element) in parallel with the button that will keep it on.

Can't really use a single pole switch as an input button then except maybe by arranging a clever voltage divider...

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You could use a switchable regulator to supply power to the IC, and use an RC circuit to slowly pull the Enable pin into the On position when the button is pressed. After the regulator turns on, a transistor connected to the output holds the enable pin permanently in the on position?

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