Firmware enhancement with device serial to device serial connection ability

[marvac01]

We started using meshcore for establishing communication on cave expeditions. But unfortunately the communication line ends as soon as diving is involved. The dive starts at a siphon that could be between a few meters up to a few hundred meters in length. The radio signal can't penetrate more than about one to two meters of stone or water.

It would be nice to be able to connect two devices via a cable at the serial interface, so that one device can be placed before the siphon and the other behind the siphon, and the communication can continue through the cable and further on from there.

Technically the setup would be about as follows:
A usb-c to rs485 module would be plugged into each device and the two modules would be connected via a (long) twisted pair cable of very unspecified quality and health (especially over time). So it might be useful to be able to select a baud rate for the connection. Even better would be a automatic connection test that tests and selects the best communication parameters on demand. (By sending some test commands back and forth?)

[liamcottle]

Hey there, this should already be supported by the RS232 Serial Bridge firmware variants.

MeshCore/src/helpers/bridges/RS232Bridge.h

Line 47 in 219812b

class RS232Bridge : public BridgeBase {

MeshCore/variants/heltec_v3/platformio.ini

Line 70 in 219812b

-D WITH_RS232_BRIDGE=Serial2

I'm not sure if we have any official docs on it, other than the original PR, but the general idea is that you compile the firmware with the serial pins you want to use for bridge mode, and then wire two repeater boards together using those pins.

Then packets received by one repeater will pass over the serial lines, and be retransmit over lora on the second board.

Please see PR #454 for more information.

[marvac01]

Ok, thanks for the info, but what does it mean?

Can the two pins also be D+ and D- from the USB Port? Because it seems that it is a rs323 implementation just on the processor pinout of the processors tx and rx pins. So it would be a RS232 protocol but with ttl level voltage, which would allow for about one to two meter of serial cable connection, connecting just these pins directly on the boards.

RS485 Adapter Modules would need the serial connection via the USB port. And RS485 is needed for the (up to) 1200m of cable length. There is already existing serial communication via the USB port for configuration and flashing via a PC. So I am not sure what would be necessary to combine that bridge version with the serial communication via USB port in a transparent way.

Maybe one of the developers of the bridge firmware variant can give some more information here.

Just FYI, here is a link (as of 2026-07-15) how these Modules could look like:
https://de.aliexpress.com/item/1005008023543983.html