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I hope I can properly explain the issue I am having right now.
Our hardware setup is a PiZero 2 with a WittyPi L3V7 Board attached to. Via WittyPi's CATHODE & VOUT pins we connect an external access point (USB-C).
In general the setup works quite well. WittyPi is booting the Pi and providing power to the external AP. But when the battery power is low, it boots both. But the Pi is no longer able to communicate with the wittypi via i2c. Moreover, the shutdown sometimes does not work correctly. WittyPi stays alive (at least the red LED) stays on. The only way to get out of that state is to completely cut all power (USB + Battery). After that I can boot all systems again, but I am not able to power down via the onboard button.
Any idea what might cause this? I have the impression, that this is only happening when the battery power is below 3,7V.
Posted : 27/05/2024 4:03 pm
To troubleshoot an issue like this, you need to measure the voltages, because our analyse can not just base on impression.
What was the voltage from the battery, and what was the actual voltage on Witty Pi 4 L3V7's 3V3 pin in unpopulated header P3/P5? If that 3V3 pin voltage was already too low, then no wonder the I2C didn't work -- afterall it is an I2C bus with 3.3V voltage level.
Red LED stays on after shutdown, most probably was because the Pi crashed during shutdown and its TXD didn't fall to 0V, or even worse the MCU (ATtiny841) itself crashed. It could happen if the battery voltage is really low, and this situation could be avoided by properly setting the low-voltage threshold. What is your current settings?
Posted : 28/05/2024 4:07 pm