I'm thinkering with a RS-485 connection (modbus) to read out my electrical power meter.
The setup is as follows:
ESP32 --> MAX3485 --> RS-485 to USB
when the ESP32 is powered via USB, on the same computer as the USB host is connected, I can see communication in both ways: The computer can read what the ESP is sending and vice versa.
When I power the ESP32 via mains power (converted to 3.3V offcourse), the computer can still see what the ESP32 is sending but when I return something, the ESP doesn't read anything.
Both ends are terminated with a 120Ohm resistor. Ground connected (I have a 100Ohm resistor in series) or not makes no difference.
I guess it has something to do with common ground but don't know how to solve...
A, B and GND connected to a generic RS-485 to USB dongle to the same PC.
Doesn't work: Same ESP, now powered via a Hi-Link mains to 5V converter (0.6A), same schematic. A, B and GND connected to a generic RS-485 to USB dongle. Mind that data sent from the ESP is still received, but the ESP itself doesn't receive anything.