I am getting strange characters on the LCD screen only when I supply the ESP32 from a separate PSU via the USB port. When I have it plugged into the PC, it works fine.
My project is controlling 3 relays and I have Positive and Negative from the ESP32 going to VCC and GND, with a separate PSU going to GND and JV-VCC. The relays are switching 220VAC.
I read that it’s important to use two separate PSUs for the relays and the ESP, but while the relays work as expected and the code runs fine, the LCD (after a while) starts to show garbage weird characters.
I checked continuity between the VCC and JV-VCC on the relay boards and my multimeter shows about 12ohms and then drops to zero. The Negative pins on the boards have continuity between them. The jumper is removed between JD VCC and VCC.
Any ideas what might I have done wrong?
We have several similar complaints here on the forum: https://rntlab.com/question/lcd_i2c-esp32-random-jibberish/
After many discussions, we still haven’t found out how to solve that issue. One of our readers suggested the following (and it actually solved the problem for him):
“put 10k pullup resistors to VCC on both the data and clock lines”
I hope this helps.