[TriEmbed] Pi power backup

[Alex Davis]

There's a good example of that here, along with a MAX486X power
protection device:
https://learn.adafruit.com/system/assets/assets/000/022/441/original/leds_schem.png?1421437847

However, it you still need to have another always-on 5v supply for the
USB power input.

In that case, why not just buy/use something like this:
http://gorillagadgets.com/products/uhuru-16800mah-portable-battery-pack-w-led-screen

I figure you can leave it plugged into the charger and when power drops
it'll just run off the battery. it wouldn't be hard to use an ADC input
(with zener diode 'regulator' to 3.3v) to monitor the charging input and
trigger a 'poweroff' when external power is removed.

I have a Pi2 setup on my car, and in my case, I use LIRC and a cheap
ipod IR remote to manually trigger a shutdown before I turn off the
ignition. Dumb, but it works.

> 
>  Dwight,
> A good method for dc power supply is to have two diodes in parallel. The
> primary source should have a higher voltage and will prevent the
> secondary source from suppling power. If the primary dies the secondary
> will kick in. So if the case is a wall power and battery power, then make
> sure you tie the grounds together and make sure the wall volatage is
> higher than the battery voltage.
> John Vaughters 



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