UPS HAT for Raspberry Pi Zero (DFR0528)

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DFRobot UPS HAT is an uninterruptable power supply shield designed for the Raspberry Pi Zero series, and also compatible with Pi 2/3/A+. The UPS HAT can continue … read more

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re: UPS HAT for Raspberry Pi Zero SKU: DFR0528

  • Is there an interrupt or other way to detect if the external supply has been lost or significantly degraded.
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Hey Tim,

Unfortunately that I know of there’s no hardware or software based solution for this. I just checked the voltage output on an oscilloscope when switching the mains power on and off and there was not a significant signal to interpret.

Software-wise, just scanning through DFRobot’s documentation it doesn’t look like they have anything mentioned about this either…

You may be able to have an external trigger that the Pi’s GPIO is constantly checking that is switched by the mains supply? Hopefully someone with a much more elegant solution can jump in here!

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Thanks Owen, I suspected as much but thought I should check just to be sure

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Hi Guys
Interesting. Surely to be a true UPS it would go through a routine to shut down the Pi in a safe manner.
What if the Pi set up is unattended. Just had a look at the “read more” link and it reads like the Pi has to be started manually. UGGGGH.
There is a bit in the product wiki which indicates this unit can communicate with the Pi via I2C. I haven’t gone any further as I lost interest.
Maybe I am a bit old fashioned but I thought a better UPS would be one which kept the Pi primary supply alive then if the interruption was short duration the system would carry on. With a large enough battery possibly for quite a long time.
Cheers Bob

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I find it hard to believe there’s no way to do it at all - I mean worst case you could just set up a resistor divider from the 5v input and tie a 3.3v level to one of the GPIO pins.

There might be something useful in the above thread.