Well, thank you,
Looking at the schematic for the Pi Zero 2W, the pull-ups on the I2C can explain the source of the voltage on GPIO 2, 3, but doesn't show how the pins are dioded or any specific detail.
However, it doesn't show anything that would explain voltage of GPIO 8-11 (unless the depiction of GPIO 2, 3 are supposed to be representative of the rest?) Looking over Raspberry Pi computer hardware, I can't seem to find any of the more detailed schematics/PCB layouts for the GPIO ports that would fill in the details. They exists somewhere, but I guess not as part of the computer hardware documentation.
One issue this raises, is if switching the power off from the Pi Zero 2W 3v3 pin doesn't actually stop voltage going to a breadboard, then what is the consequence of the partial voltage sitting there for extended periods of time for whatever else you have present on the breadboard? Do the remaining current-paths pose any risk to the Pi or components on the board? I've often just pulled the 3v3 or 5v supply from the Pi to a breadboard thinking that was removing the voltage, but this shows, at least with I2C and SPI, that isn't quite the case. The goal being to prevent any stray voltage from causing damage if something conductive happens to slide into an exposed resistor leg or the like.
Do you have a url for the detailed schematics of the Pi Zero 2W GPIO pins that would show protection diodes, etc.. to confirm how this voltage is feeding back? I guess it's also the ADS1115 and MCP3008 that don't provide any protection for comm-pin voltage feeding back through the Vcc and ground pins when Vcc is removed.
Looking at the schematic for the Pi Zero 2W, the pull-ups on the I2C can explain the source of the voltage on GPIO 2, 3, but doesn't show how the pins are dioded or any specific detail.
However, it doesn't show anything that would explain voltage of GPIO 8-11 (unless the depiction of GPIO 2, 3 are supposed to be representative of the rest?) Looking over Raspberry Pi computer hardware, I can't seem to find any of the more detailed schematics/PCB layouts for the GPIO ports that would fill in the details. They exists somewhere, but I guess not as part of the computer hardware documentation.
One issue this raises, is if switching the power off from the Pi Zero 2W 3v3 pin doesn't actually stop voltage going to a breadboard, then what is the consequence of the partial voltage sitting there for extended periods of time for whatever else you have present on the breadboard? Do the remaining current-paths pose any risk to the Pi or components on the board? I've often just pulled the 3v3 or 5v supply from the Pi to a breadboard thinking that was removing the voltage, but this shows, at least with I2C and SPI, that isn't quite the case. The goal being to prevent any stray voltage from causing damage if something conductive happens to slide into an exposed resistor leg or the like.
Do you have a url for the detailed schematics of the Pi Zero 2W GPIO pins that would show protection diodes, etc.. to confirm how this voltage is feeding back? I guess it's also the ADS1115 and MCP3008 that don't provide any protection for comm-pin voltage feeding back through the Vcc and ground pins when Vcc is removed.
Statistics: Posted by drankinatty — Wed Oct 22, 2025 10:22 pm