Arduino Micro to Arduino Micro serial communication via a host bridge

float foo

So, I have this sketch which puts out a newline-delineated string of text, specifically V=(foo,4) over the USB serial port every 500ms or so.

That sketch is supposed to interface with another sketch running on another arduino (which is handling a power supply).

If I use the arduino serial monitor, I can easily read and write to either serial port - the problem is attempting to cause the two to communicate.

First, i tried good old cat </dev/ttyS3 >/dev/ttyS5. //power supply port and drip feeder port, respectively.

Got reaaaaally excited because it worked, once, and then stopped adjusting based on S5's output value. when this occurs, I have to reset the terminal session (but only in putty, not arduino's serial monitor) before I can successfully set values.

So, I got a little fancier, and wrote a python script to null modem the two together - worked, but unreliably. worked best parsing the contents of the entire buffer, but it still occasionally locked up, also wasn't fast enough by a long shot.

Socat, when run on cygwin on my win10 machine, won't touch the serial ports, because "invalid attributes".. 4 -d's deep, and it's pulling an all zeroed array from some class I don't understand shrug.

But one thing I do know, is that I'm not really all that unique, and there very likely is someone in here who can help.

Attached, please find the sketch I can't change, even if i could get it to compile:
the python and 2nd arduino's sketch can be uploaded tomorrow if needed.

HY30005EP_display.zip (39.9 KB)

Why the difficult way?

Connect RX of #1 to TX of #2 and TX of #1 to RX of #2. Connect the grounds of #1 and #2.

Use Serial1 for communication instead of Serial.