Guys, I made a simple project with a PIC16F877 and a MAX5389, which is a digital potentiometer. I'm just connecting the UP/Down and Inc terminals directly to the PIC.

Both the PIC and the MAX5389 have a 100nF capacitor next to the VDD and GND pin.

The PIC also drives a transistor, which drives a relay to activate a contactor.

It doesn't happen every time, but sometimes it happens that when activating the contactor, the MAX5389 resets and returns to the average resistance value it has when it is initialized (on power-up).

How can I resolve this?
Swap the 100nF capacitor for another one?
Also include capacitors in the two connections between the PIC and the MAX5389 (On the connections with Up/Down and Inc).

 

Likely noise from the relay and contactor.

Do they both have noise suppression circuits across their coils to damp the inductive spike?

The ground from the relay and contactor should go to the power return on a separate wire from the PIC common (star connection).

 

Contactor has noise suppressor.

PIC ground is not the same as relay and contactor

 

Schematic and pictures. please

 

I don't have the schematic

 

Schematic of PIC-pin? to transistor to contactor.