Mains failures killing DIGI Hats

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1

PI 4b, HiFiBerry Digi pro, Volumio 3.832
Where I live in the UK we get random and unexpected loses of Mains supply, maybe two or three times a year. I bought a UPS to supply my HiFi setup and on the whole it does a good job except for the HiFiBerry DigiPro2 Hat on my PI. It seems to die when this happens.
I am pondering on what I can do to protect it. The PI and its Hat are supplied by Shanti 5V linear supply so my only thought is that it is the difference in boot times between the PI and the DIGI that could be the cause, but it is just a guess.
Has anybody else experienced this and come up with a solution?

2

Hey @AudioPete,

Yes, what you are describing makes sense. The HiFiBerry Digi+ Pro (and Digi2 Pro) has its own clock and logic section powered through the 5V GPIO rail, but the hat’s initialization timing is quite sensitive during brownout or asynchronous power recovery events. When the Pi and Digi board don’t rise at exactly the same rate after a short power dip, the HAT’s EEPROM or I2S section can fail to register correctly, leaving it “dead” until a full power cycle.

Some users have mitigated this with one of these approaches:

  • Add a very short power delay (relay or power sequencer) to the Pi, ensuring the DAC HAT’s 5V stabilizes first.
  • Alternatively, keep both the Pi and the Digi on the same UPS outlet, but insert a 1–2 second boot delay script in /boot/config.txt (for example boot_delay=2) so the Pi waits for the HAT to be fully powered before probing I2C.
  • If your UPS has a “hold-up” dip when switching from mains to battery, an inline 5 V supercap or secondary power smoothing module (Pi UPS HAT or PicoUPS) can help stabilize it further.

It’s not unique to HiFiBerry; Allo DigiOne and similar boards with dual oscillators or isolated S/PDIF stages show the same behaviour on unstable or staggered power-ups.

Kind Regards,

3

Thanks @nerd, and your suggestions, pleased I could be on the right track.
I learnt, only this week, that the DIGI Hat is not actually dead after the last mains failure, but was unresponsive, it came back to life after a couple of 5V power cycles.
I think the Shanti 5V linear PSU probably covers your 3rd point so I am going to try your boot delay idea first to see if that does the trick.
I will post again when I have more info.

4

Added the boot delay line to userconfig.txt, it is now wait and see.