Qwiic Single Relay locks up

Qwiic System
1

I have three of these relay modules. They work fine with no load connected to relays. They lock up when load is applied.

I am running the Example1_Single_Relay_Basics program to test the relays. The program has been modified to allow the modules to be attached to the I2C Mux. I also modify the program to select a relay to test.

If I disconnect the load and run the program, I get the expected on-off-on-off and the program completes.

If I connect the load and run the program, I get the on but never an off and the program hangs somewhere.

If I reset the microprocessor, the test starts again and fails again.

2

If you have an inductive load (like a coil), make sure to apply a fly-back diode to control the spikes that happen during applying and removing the power.

3

This is a 16V AC application switching about an amp. Don’t think I can use a diode. What protects the microprocessor on the relay board from the relay? My logic analyzer shows strange transistions on the I2C bus when the relay turns on.

4

TVS diode or MOV (at the relay output), rated for you application, can be used to clamp spikes.

Also, you could need opto-isolation between uC and high-power relay; but I would start with the TVS/MOV first.