ESP8266 emonTX Serial to EmonCMS over WiFi

Do you have an emonTX, emonTH or any other serial printing sensor node that you wish was internet enabled? This might help then.

What is it

This is a small ESP8266 (Arduino IDE support) sketch that forwards the data it receives over Serial to EmonCMS (soon MQTT support as well).

Total cost should be something like $4, a lot less than a RaspberryPI gateway plus a RF module. On top of it all, I am programming my ESP8266 modules with the same IDE and language and programmer I am using for my emonTX, already had everything.

This is not really useful for battery powered nodes. ESP8266 modules are quite power hungry. You should also not power the module from the emonTx, it draws too much.

What do you use it for

I use it to forward all my emonTX v3 readings to EmonCMS without needing to have a RaspberryPI gateway with a RMF12PI at all.
It is however not limited just to emonTX, any device that can output serial data could be made to work like this.


  • ESP8266 module with separate power supply
    ESP-01 will do, schematic soon
  • ground of ESP module must be connected to ground of sending device
  • Serial baudrate to be the same on both sending device and ESP module
  • Serial sending format to be

This format is the format that most of the emonTX sketches output. In some case you will need to enable debug, in others you will need just a small modification to the sketch to add NODEID or to remove extraneous text amongst values.

Getting started

emonTXSerialGateway Getting Started on Github


  • add MQTT support
  • more error checking
  • … ideas, pull requests, issue reports are all welcome 🙂

Get it on Github

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- November 25, 2015