I have a setup with two Raspberry Pi Zeros that monitor each other. They regularly check whether the other Zero is still sending data via the serial port, and if it's no longer detected, the other Zero is reset via a relay.
The relay is controlled by a transistor using port GPIO 21 (pin 40), and that works.
However, when the second zero restarts, the first one is also reset because the relay (connected to the second zero) is also energized briefly.
I understand that the GPIO ports on a Zero are switched as inputs during bootup, with some having pullup and others, including GPIO 21, having pulldown.
Can anyone tell me if GPIO 21 is briefly "high" during bootup, or should I look for the problem elsewhere?
And what could be a solution?
The relay is controlled by a transistor using port GPIO 21 (pin 40), and that works.
However, when the second zero restarts, the first one is also reset because the relay (connected to the second zero) is also energized briefly.
I understand that the GPIO ports on a Zero are switched as inputs during bootup, with some having pullup and others, including GPIO 21, having pulldown.
Can anyone tell me if GPIO 21 is briefly "high" during bootup, or should I look for the problem elsewhere?
And what could be a solution?
Statistics: Posted by GermoV — Sat Jan 17, 2026 2:30 pm — Replies 5 — Views 74