OpenEnergyMonitor Community

EmonTx integration

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Hi! Sorry for the beginner question. I have already a self-developed system composed of a RPI3 that acts as a central device (with a display) and some NodeMCU-based sensors in my home that transmit data to the RPI using WIFI over my local network. I would like to integrate EmonTx board, being able to use the same approach (i.e. send the power measurement to the RPI’s IP address). Is it possible? Can I connect one of my NodeMCU board to the EmonTx board, get the results and send them to my RPI?
Thanks a lot.

Welcome, Andrea, to the OEM forum.

What do you mean by

There’s the emonTx which is a complete, cased unit, that normally sends the data by 433 MHz ISM band radio (but you can use the serial data output); or there is the emonTx Shield, which is a Shield for an Arduino Uno that has the analogue interface and the same ISM band radio.

The OEM shop does offer the emonTx with WiFi adapter:

I am not a NodeMCU expert, however that might well suit your application.

Otherwise, if one of your NodeMCU boards can run with a serial input, and (if it would send random data to the emonTx you don’t connect the serial output), then you should be able to use it. It will need its own power supply, as the emonTx does not have the amount of surplus power available that’s required for WiFi.

As you are in Italy, will you require a 3-phase emonTx? The default software was written for the UK domestic single-phase electricity supply, and won’t give the correct values on a 3-phase system. Note the 3-phase sketch can only work up to 9600 baud.

Hi Robert!
Thanks for your prompt reply.

By emonTx board I mean this one, so I think I just used the wrong words :slight_smile:

NodeMCU has UART connection so I guess I can use it to talk with the emonTx.

Single-phase works fine for me, we have the same domestic supply here in Italy.

I have another question: I noticed that emonTx can use batteries instead of a plug. Does it mean the AC-AC Voltage adapter is not needed in this case? I read that using batteries the measurements are less precise but as far as the error is around some tens of watts it is fine to me. I would prefer to have no need of power connections (a part the one for powering up the wifi module).

Thanks a lot!

Sorry, I can’t give a detailed reply as my laptop has died.

The emonTx will also come with a less precise sketch if you want the battery option -it’s not recommended.

Hi Andrea,

When the emonTX is powered by batteries vice using a 9 Volt AC-AC adapter, the measurements
it makes and reports are approximations of apparent power. (measured in Volt-Amps)
The firmware assumes a nominal AC voltage (230 V IIRC) but mains voltage varies up and down all day, every day. Essentially, you end up with an estimate that varies constantly.

Thanks to everyone for the support. I’ll go with the one with the AC-AC adapter.