Small AC motor + LCD problem

Hi everyone, I am building my own incubator and I am using a small AC motor (from a microwave) to turn the eggs. The motor is controlled by Arduino and a 12 V relay module that I made myself with a transistor and a optocoupler. Everything is working fine, except that when the motor is powered I have some issues with the LCD: it displays the right value of humidity (e.g. H=45) but also two more digits (e.g. H=4573). The humidity level is calculated from wet bulb temperature. The error persists even when the motor stops. Could this problem be related to noise from inductive loads? If so, could a zero-crossing Ssr limit the surge current and solve this problem? Thank you

Problem is most likely in the code you didn’t post. Please read the sticky on how to use the forum, especially #7.

Did you erase the LCD before printing?

Wiring layout and shielding are important factors if EMI is causing the issue.