Allan Herriman wrote on 10/15/2017 3:42 AM:
> On Sat, 14 Oct 2017 20:18:36 -0400, rickman wrote:
>
>> I was looking for a Li-ion power source adapter and found this in the
>> process.
>>
>> http://www.ebay.com/itm/112419803835
>>
>> Looks like it would serve as a UPS for a rPi in many situations.  The
>> listing isn't big on specs, but they seem to show it will drive well
>> over an amp in a pass through mode.  They talk about a couple of amps on
>> each of two ports in power bank mode.
>>
>> I know this has been kicked around a bit here, but I  don't know if
>> anyone found an economical solution.  This unit is around $10 and a
>> Lithium battery will cost around another $4 or $5.  You can either use
>> the standard 18650 type or one of the Lithium polymer flat cells.  Both
>> seem to be available cheaply with about 3000 mAHr capacity running a
>> typical pi for around 2 hours.
>
> Looks ok to me, if all you want is a power bank controller that can
> charge and discharge at the same time.  You might find you can buy a
> complete power bank (including the Li cells) for about the same price if
> you shop around.  My local computer store was selling Romoss Sailing
> models on sale for ridiculously low prices recently.
>
> To be a useful, general purpose UPS though, it needs to be able to output
> a signal to tell the load (Pi) that it's about to run out of juice so
> that the Pi can shut down cleanly and go into a low(er) power state, all
> without corrupting the SD card.
>
> Assuming you can figure out how to derive such a signal (e.g. by
> monitoring cell voltage, or by starting a timer when the charging input
> fails), I guess you could try to couple it to something like this:
> https://shop.pimoroni.com/collections/raspberry-pi/products/onoff-shim
>
> "It watches the state of BCM pin 17 and, when pulled low (pressed), it
> initiates a clean shutdown. Last thing, just before your Pi shuts down,
> BCM pin 4 is pulled low to completely cut power to your Pi."

If the Pi pulls BCM pin 4 low to cut power (I assume on the power source)
how does the circuit get powered back up?  Once power is cut, pin 4 won't be
pulled low anymore.  I guess it has to be a momentary input controlling a
state on the power controller.  Then something else has to change the state
and turn power back on?

--

Rick C

Viewed the eclipse at Wintercrest Farms,
on the centerline of totality since 1998

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