I’m using my Photon in a Sparkfun WeatherShield powered by a solar panel and battery. Unfortunately, a wire from the panel fell off last week, the battery ran down, and the Photon committed seppuku. Particle was very gracious in sending me a new one but I can’t be swapping out Photons every time the battery goes too low.
Is there some system call I can give to gracefully shut down the Photon if the battery falls below a certain threshold? There are a number of other threads on this topic but they’re for the Electron. There’s one for the Photon but I didn’t really see a solution there.
@Michele, the only “shutdown” would be to put the Photon in non-timed (ie forever) deep sleep using System.sleep(SLEEP_MODE_DEEP);. I believe, possibly wrongly, that this situation has been addressed in the most recent firmware versions. Perhaps @mohit or @BDub can clarify?
That’s strange. The first Photon I had in the WeatherShield was in fact able to recover from low battery conditions just fine. I bought that one in March. Unfortunately, it died a horrible death when I accidentally brushed the Vin jumper against the direct output of the solar panel which was producing over 18 V at the time.
The Photon that died last week and can’t be resuscitated is one I just bought a month ago. Perhaps they’re not shipped in order of manufacture? Is there anything printed on the device that would indicate how recent it is?
Deep sleep might help, but I don’t know how I’d get it to wake up again when the battery power returns.
Perhaps I need a circuit that disconnects the Photon if the battery goes below 6 V and then reconnects it when the battery is recharged to 12 V. That would allow automatic restart if we have a string of cloudy days that drains the battery.
If you are lucky you only blew the regulator and might be able to replace that.
The circumstances why devices sometimes die due to "browning out" are not yet fully understood and a "fix" that was added a while back obviously wasn't the final solution. But it's investigated.
It doesn't always happen either - hence you may not have run into the same thing with the other Photon.
Well I wasn't lucky. I tried running it from my bench supply directly to the 3v3 pin and all that did was release the magic smoke 
The new one just arrived today. I don't know, what do you think - should I try putting it on the bench supply and slowly running the voltage down to zero and see what happens? Will Particle send me yet another one if this one gives up the ghost too? I guess what I have to ask myself is "do I feel lucky?"
The circumstances of dim D7 are mysterious, but we do know that just lowering the voltage using a bench supply is not enough to trigger the problem, as that was one of the first tests that was done and doesn’t seem to be able to cause the failure.
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Well then I won’t bother with that test. If nothing else, I’m working on a voltmeter display that will display the battery voltage on the weather station LCD panel. Then I can run outside and disconnect it if it goes too low.