I think you need to reflash the EmonTX. I’d be concerned about the serial output that is shown here as ?
.
I did this successfully via the PIO method on a PiZero (I updated the docs), but you need the RTS line connected and change the pin number, else Robert’s way with a programmer and Arduino IDE.
[edit]
Also note if you use the PIO method, you need to install the library first. The docs were written with this line in the platformio.ini
file
lib_deps_external =
https://github.com/openenergymonitor/EmonLibCM.git
But @glyn.hudson changed it back to just EmonLibCM @2.4.1
, but this means you need to install it manually rather than have the PIO package manager do it for you.