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[Solved] Witty Pi 4 - Low Voltage Threshold Issue

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I'm trying to make sense of these messages in the Witty Pi 4 log file (wittyPi.log):

[2023-08-22 02:20:51] Shutting down system because input voltge is too low: Vin=3.63V, Vlow=3.1V
[2023-08-31 14:16:50] Shutting down system because input voltge is too low: Vin=3.63V, Vlow=3.1V

I can confirm that I had the low voltage threshold set to 3.1 volts, but as you can see in the messages, the measured voltage was well above that when Witty Pi decided to shut things down. For now I have disabled the low voltage threshold setting, but I'm definitely wanting to understand this behavior.

Posted : 07/09/2023 7:47 pm
Posts: 75
Member Admin

The low voltage detection is done by the firmware and you can see how it is implemented here.

When low voltage is detected, the firmware will write some I2C registers and then emulates a button click to shutdown Raspberry Pi. The software ( detects that emulated button click and writes the message about this shutdown into the log. The messages you referred were created in such scenario.

In the message, the Vin value was taken from I2C registers #1 and #2, which was measured at the moment you requested the I2C register value. The firmware doesn't cache the voltage value that was detected as low-voltage, so there is chance that the newly measured voltage has changed already. This situation might happen when the input voltage is not that stable.

Although the log message you referred is rather confusing, the board's behavior is correct and the input voltage has ever dropped under 3.1V and that caused the shutdown.

This post was modified 2 weeks ago by uugear
Posted : 08/09/2023 3:51 pm