How does the hardware generate correct voltage for RS232?

[GitGoingBrains]

I've been researching programmatically communicating with Elecraft KX2s (and KH1s) via esp32 boards, just as SOTAcat does. Most online sources say that RS232 typcially runs 12V +/-, I'm sure all older serial ports did. I'm pretty sure the ESP32C3 in this project is just sending 3.3V or so. Is that true?

I'm not great a C programming, just learning via Arduino at the moment, so I also find it hard to find and understand how to send and receive responses to KX2 commands in the SOTAcat code base. Any pointers would be appreciated!

[jeffkowalski]

See the schematic at the bottom of this page: https://github.com/SOTAmat/SOTAcat/blob/main/Docs/Hardware/SOTACAT%20BOM%20-%20schematic%20-%20assembly%20instructions.pdf
There you will see a Rx voltage divider to cut the 12v from the KX2 to 3.3v for the ESP32. Tx signals directly out at that level.

All communication with the radio is contained in kx_radio.cpp

[GitGoingBrains]

Thanks for that. I had seen the resistors dividing voltage for battery level measurment, but I hadn't seen the label on the resistors on the far right, as you've said, for dividing ~12V down to ~3.3V. It's great to know that tx to the radio can be at the 3.3V level without need to boost it up in any way.

kx_radio.cpp is definitely where I need to spend some time! Thanks again BX2AKP Brian