Schrijver: KeesJan

After some efforts, I got the Atom RS232 kit to work fine ..
These are my observations/experiences:

1. the shield Transmit line is labeled with a blue R, the shield Receive line is labeled with a green T. I guess this Oriental logic: please connect the receive line of the other device to this device R transmit line.

2. Using Arduino 1.8.13 and the ESP32 1.0.4 board library, initially the board would only transmit data. The shield works fine with other Arduino/ESP units. When connecting other shields to the Atom, they suffer from the same problem. I pinned it down to a problem with the Atom pin 22 line: when I use another line as transmit line it works fine. The final solution was to patch the shield and connect pin 22 with pin 23 and initialize Serial2 to use pin 23 and 19:
Serial2.begin(38400,SERIAL_8N1,23,19);

3. when the shield is powered by the 5V of the Atom, it outputs 0V (low) and +12V (high). This was kindly accepted by all other RS232 devices that I tried. The RS232 specs state that the low level must be below -3V, so you might run into (older) equipment that requires that.

4. when the shield is powered by the external 12V, it correctly outputs the -12V (low) and +12V (high) levels as stated by the RS232 specs.

I guess that the pin22 problem is caused by a bug in ESP32 board library, or the ESP32 core, if you know how to fix it, please let me know !