mcp23017 resets and relays stop working!

Question

Hello,

I have attached AC fan as load to my SainSmart 8 Channel DC 5V Relay Module.

The relay board is supplied with external power supply(5V,1Amp).The relay board is controlled by MCP23017(gpio expander ic connected to my raspberry pi).

The fan is with Regulator.Sometimes when i change speed from regulator the ic is reset and relays stop working.

jw0752 · Answer

Hi Nilay, Could you clarify your explanation of the circuit setup. You mention an AC fan but how are you powering the AC Fan. I guess the most likely cause of the problem is a voltage spike or voltage dip is pulsing your power feed to the logic circuitry. This in turn causes the logic circuitry to reset. Usually you can protect yourself from this by using decoupling capacitors on the power rails or by isolating the power supply to the logic circuitry from the power management circuitry. John

Problemchild · Answer

Sounds very much like it John, I assume it's some kind of speed controller rather than a regulator as such. If so and it switches at any old time rather than say at zero crossing the spikes could indeed be quite large however it's amazing it does this considering those relay modules also have opto isolation and he's using a different power supply. Nilay can you lay out your circuit diagram so we can see it ...cheers