On 31/7/25 16:41, Joe wrote:
RS-485 and RS-422 use cables with a specified impedance, unlike RS-232, so can work over much longer distances and/or at higher speeds. I've had RS-485 working over a kilometre of cable at 9600 Baud. RS-232/V-24 is only really reliable over about twenty metres at its highest speed.
The Pi Serial (UART) implementation uses 0v and 3V3 as signal levels at some quite low current capability. If you get 1m distance you will be doing well.
One trick is an adaptor card that converts to RS-232 or RS485 level signals, that as you mention can go 20m or 1km. This still runs the UART signal protocol with start bits and stop bits and baud rate.
Another embodiment converts the 3V3 UART levels to USB protocol and you can go as far as a USB cable can run. But note that the signal that goes down the cable is no longer UART/Modem signals but a completely different signal level and protocol that carries the serial data as a payload in a much more complex protocol.