I connected up an 8-channel Waveshare relay board to a Pi 5 running the latest OS.
On applying power I can hear a relay(s) click.
After the OS has started, relay LEDs for channel 3 and 8 (P13 and P26) light.
Looking at the schematic, there must be enough of a ground potential voltage on P13 and P26 to activate the relays but not the LEDs.
Either the GPIO lines have been set as outputs during power-up, or there is a lower than usual resistance to ground for these two lines.
After the OS has started, the resistance or voltage on these two lines drops enough to light the LEDs.
Does anyone know for sure what is happening ?
I don't think its a GPIO library issue as the relay(s) click on power being applied, and then the LEDs come on after the OS has started.
I am doing a POC for work and fortunately I only need 6 relays controlled (for now).
On applying power I can hear a relay(s) click.
After the OS has started, relay LEDs for channel 3 and 8 (P13 and P26) light.
Looking at the schematic, there must be enough of a ground potential voltage on P13 and P26 to activate the relays but not the LEDs.
Either the GPIO lines have been set as outputs during power-up, or there is a lower than usual resistance to ground for these two lines.
After the OS has started, the resistance or voltage on these two lines drops enough to light the LEDs.
Does anyone know for sure what is happening ?
I don't think its a GPIO library issue as the relay(s) click on power being applied, and then the LEDs come on after the OS has started.
I am doing a POC for work and fortunately I only need 6 relays controlled (for now).
Statistics: Posted by dreul — Fri Feb 06, 2026 11:30 pm