That should be possible, but you’ll probably need to modify the sketch to do it. (You might need to remove the “human-friendly” diagnostics at start-up.)
It sounds as if your emonTx is a V3.2 - does it have a RFμ processor module on a piggy-back board, with the RFM12B radio module on that?
Not directly, you will need to make a few small changes. I suggest you get hold of the V3.2 sketch and use the hardware settings from that to “backdate” the V3.4 sketch.
The most important change is it needs a different software library -
(which you’ll need to download and install)
You’ll want to remove the DIP switch code and the battery monitor (you don’t have either). Pulse counting is on a different interrupt and pin, as is the RFM module. I’ve attached my crib showing all the different I/O. If you search for the things that are different in my crib sheet, you should find what needs changing.
Both need to be present when you compile with the IDE - but only the combined executable gets loaded. (It will complain if one is missing.)
So does ours. It’s best if you calculate for your a.c. adapter. “230” is the nominal input voltage, “(9V × 1.2)” is the measured output voltage on no-load at the nominal input voltage, and 13 is the nominal voltage divider ratio inside your emonTx (which is the same for V3.2 & V3.4). (This is in Learn: Current & Voltage).
Your best answer to this is to get hold of the circuit diagram! It’s well hidden at Git/Hardware/emonTxV3/archive-emonTx_V3.2
You can feed it 5 V on the terminal strip (see the PCB legend) - that’s the easiest.
emonTx IO-all .html.txt (5.0 KB)
(Rename to .html & view in a web browser.)