mcp23017 resets and relays stop working!

Hi Nilay, I see nothing intrinsically wrong with your layout. The fan may be creating enough of a spike when the speed changes to affect the house mains. Depending on the sophistication of your 5 volt supplies this spike may be getting through. Try putting 100 uF caps across the Vdd - Vss on the Pi and MCP23017. The only other possible situation is if the Pi and MCP boards are very close to the 240 volt power feed to the AC we might be getting some inductive coupling.

John

Thanks alot  sir,

il surely try with the capacitor and let you know the results soon.

just a doubt, the spikes that i observe are bcoz of the speed regulator from relays reseting the ic .so why to set up the capacitor between pi and ic and not between relays and ic ?

Hi Nilay, The capacitors should go between the power rails, as close to the boards as possible. Watch the polarity. I sugested one capacitor between the power rails for the Pi and one capacitor between the rails of the MCP as they are the most susceptible to spikes. You did indicate that it was the MCP that was resetting. Give it a try and if it doesn't solve the problem let us know. John Alexander is following this thread too and he is actually a lot more knowledgeable than me and he will let us know if there are better options to try.

John

It's hard to be sure but another possibility to look for is that the regulator is opening and closing the mains circuit causing large very high frequency transients. If you set up the fan and regulator not connected to your relays but with the wires physically close does it still affect the rest of the circuit ? If it does then you will need to do something about the regulator but I'm not quite sure what (without knowing what is inside it.) If the problem only occurs with everything connected you could try winding the two wires GND and GPA0 from the MCP32017 to the relay board several times round a ferrite lump (like Farnell 2364660).

MK

oh yes definitely sir its my privilege that my thread got noticed and guided by experts like John Alexander. i do share the same concern what john sir mentioned earlier that inspite of such a stable circuitry of sain smart relays (opto isolation) voltage spikes is affecting my MCP.Anyways ill try out the capacitors and get back here with the results in a while. 

oh yes definitely sir its my privilege that my thread got noticed and guided by experts like John Alexander. i do share the same concern what john sir mentioned earlier that inspite of such a stable circuitry of sain smart relays (opto isolation) voltage spikes is affecting my MCP.Anyways ill try out the capacitors and get back here with the results in a while.