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Project Progress

This page is for a product in current development. Hardware units are now ready and can be purchased here.

Software is still under development. A first release will be available end of May 2018.

EmonWRT3 Wifi Energy Monitoring Device with OpenWRT

Buy it online here.

EmonWRT3 is a one unit system for energy monitoring. It measures usage of an electrical installation and post data on a server (Emoncms or other). You can then view the data on your computer or phone.

It combines the Arduino based microcontroller and OpenWRT wifi module together. EmonWRT3 interfaces with sensors like Current Transformers/ Temperature and Voltage.


  • Simple to use with web interface for configuration.
  • Connect with Wired or Wifi.
  • Wall mountable.
  • Single box system.
  • Open source components OpenWRT and Arduino.

EmonWRT vs Raspberry Pi. The main motivation for developing the EmonWRT was to increase robustness. For the long run the RaspberryPi solution can become vulnerable due to the operating system hosted on a SD card. High quality SD cards can be used but a higher risk of failure still remains. The EmonWRT contains the operating system on an embedded flash memory and will solidly keep on running.

Technical Specifications

  • 3 Current Sensor Ports
  • 1 AC/AC Volatege Port
  • 1 Temperature Sensor Port
  • 1 Ethernet Port
  • 1 MicroUSB Power Supply port
  • Operating System: OpenWRT Chaos Calmer
  • Micro Controller Unit: AtMega328 (Arduino)
  • Wifi (internal or external antenna)
  • PCB Dimensions: 55x55mm
  • Enclosure Dimension: 80x60x27mm

Recommended Sensors

Current: SCT-013-000
Temperature: DS18B20
AC/AC Adaptor: 77DB-06-09 77DE-06-09 77DA-10-09


IP Address (Wired LAN):
Username: root
Password: To be set on first use.


The EmonWRT3 is made of the following components.

  • EmonWRT3 CT3V1T1 Base Board
  • Skylab SKW71 Wifi Module (OpenWRT)
  • Atmega328 Microcontroller (Arduino)
  • 3D printed enclosure.

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Internal Dataflow

Internally the Arduino mcu collects data from sensors on the ADC port and transmit them to the OpenWRT module via serial interface.

Then the OpenWRT module transfer all data to the specified web server (Emoncms, InfluxDB etc...) using conventional ethernet protocols.

The configuration of the unit is using the Luci web interface that comes with OpenWRT. One can at easyly configure the EmonWRT to connect to a wireless network.


The web interface

OpenWRT uses Luci for configuration. The EmonWRT has a page on Luci where APikey, emoncms server and node ID can be configured.

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Apikey is the long number that identify the account on the Emoncms server. It can be found on the emoncms server in the API help page. The Read & Write apikey key should be copy pasted here.
EmonCMS Hostname is the location of the emoncms server to use. It can either be emoncms.org or your own server. If using your own emoncms server you might need to indicate the full path here. e.g.
Node ID is a number that identify the device. If you have several EmonWRT (or emontx) you can change this number here to differentiate between them on the server.

Background Configuration

The actual configuration is saved in a text configuration file /etc/config/emonwrt3.


Default Sketch - coming soon


(New) Install/Update EmonWRT on WR703N

Version History



EmonWRT Software


  • Support for OpenWRT Attitude Adjustment


  • Support for OpenWRT Barrier Breaker

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