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ESP8266 emonTX Serial to EmonCMS gateway

What is it

This is a small ESP8266 (Arduino IDE support) script that forwards the data it receives over Serial to EmonCMS.

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.

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

  • download this sketch
  • download all the libraries mentioned in the sketch and put them in your Arduino IDE's libraries folder
  • get and add your write key to the sketch
  • modify your emonTX sketch to print in the requiered format
  • burn the sketch to your ESP module
  • connect ground to ground and emonTX TX line to ESP RX line (on emonTX v3.4 the TX line is labeled RX as on the programmer, connect to RX)
  • start them up
  • if you included the WiFiManager library it will start an access point for you to easily configure which access point the ESP will connect to
  • after it restarts you should start seeing data in your EmonCMS account


  • add MQTT support
  • more error checking
  • ... ideas, pull requests, issue reports are all welcome :)


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