I have 6 3V reed relays SIL03-1A72-71D that connect to a raspberry pi pico directly via gpio pins 11, 12, 13, 14, 15, 18, and 19 on a custom pcb. The connections to the relays are: 1 is connected to 12V, 3 is connected to the pico, and 5 and 7 are grounded to a ground plane. The relays are meant to actuate a pinch valve (the schematic is flipped because I found that the way I drew it was wrong). The pico is also connected to two Sparkfun MAX31855K thermocouple readers via spi using pins 2, 3, 5, and 6.
Currently, I can read from the thermocouple readers normally, but when I turn the 12V power on, the temperature that is read slowly drops from 21 to 0 and then 4091. The pinch valves still actuate normally and everything, but I cannot read the thermocouples normally. When I turn the 12V power off, the thermocouple immediately goes back to normal. What could be happening here?
I checked for continuity all over the board and didn't see any shorts. There is no direct connection between the relays and the thermocouples. The setup actually worked sometimes when not all of the pinch valves were plugged in but then it went back to not working when I looked at it again. Two issues I think there could be are that maybe the relays overheated when I soldered it and broke or that there is some EMF being generated that is messing with the SPI output. I am not an electrical engineer but have been working with microcontrollers and robotics for awhile.
