Theo  wrote:
> Michael J. Mahon  wrote:
>> A small, non-backed-up 5v wall wart will provide a logic level that goes
>> low whenever mains power fails. Two resistors will convert it to a 3.3v
>> logic level.
>
> Good idea.  I'd probably make those resistors fairly low value, otherwise
> the output capacitor may hold charge as long as it can sustain the leakage
> on the Pi's GPIO (very long) before the voltage drops enough to signal the
> failure.

Agreed. A total resistance of 1K (5mA) ought to be fine, since a couple
second delay is appropriate.

> However it won't tell you if the power bank is getting low - eg if the power
> came back after an outage (so the power bank is near empty) and then goes
> out again.

True, but battery run time should be at least several minutes and shutdown
time several seconds, so this is certainly a second-order effect, down by a
couple orders of magnitude.

> Theo
>

--
-michael - NadaNet 3.1 and AppleCrate II:  http://michaeljmahon.com

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