Allan Herriman wrote on 10/17/2017 6:48 AM:
> On Mon, 16 Oct 2017 21:31:06 -0400, rickman wrote:
>
>> 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?
>
> That board is an on/off controller, rather than a full UPS interface.  It
> only has two 3-pin SOT23s and one 5-pin SOT23 on it, so don't expect too
> many smarts.
>
> I only meant it as a source of ideas, not something that you would
> actually use, particularly at that price.
> The Python script that makes it work is probably more interesting than
> the hardware.  If you reuse those exact GPIO pins, you could use the
> script without modification.
>
> Any UPS solution you come up with will need to do something similar.

Yes, I'm just trying to think it through.  I think for many 24/7 apps, you
would want the rPi to power back up when the mains power returns.  I believe
that is an option on most PCs.  Likewise it should be an option on the UPS.

--

Rick C

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

--- SoupGate-Win32 v1.05