System Overview

The OpenEnergyMonitor system has the capability to monitor electrical energy use / generation, temperature and humidity.

The system is made up of four main units. These can be configured to work for a variety of applications. The system is fully open-source, both hardware and software. All hardware is based on the Arduino and Raspberry Pi platforms.

Current system


emonVs v1.3.2:
Combined precision voltage sensor and power supply, sends voltage data and power to the emonPi2 via RJ45.


emonPi2 v2.0.1:
A Raspberry Pi shield offering 6x clip-on CT current sensor inputs, Real/Active power measurement, temperature sensing and radio transreceiver.


CT sensor: Current transformer. Used for measuring AC current. We use a non-invasive clip-on sensor for ease of installation and safety.


emonCMS: An open-source web application, for processing, logging and visualising energy, temperature and other data. Runs locally on the emonPi and emonBase, also available remotely via


Open Energy Monitor has developed and evolved different hardware solutions overtime:


Earlier hardware


emonTx v4: A 6x circuit energy monitoring node. Transmits data via an inbuilt 433MHz radio to an emonBase. It can also send data via a Wi-Fi extension board or directly via USB.


emonBase: A Raspberry Pi base-station that receives data sent from the emonTx4. Hosts the emonCMS software for full local data logging and visualisation capability. With new direct SPI RFM69 radio transceiver.


emonPi: An all in one 2 circuit energy monitor and base-station which collects data, hosts the emonCMS software and can also receive data from other sensor nodes.


emonTx V3.4: A 4 circuit energy monitoring node. Transmits data via an inbuilt 433MHz radio to an emonBase or emonPi. It can also send data via an ESP8266 WiFi adapter or directly by a serial connection.


emonTH: A battery powered, wireless, room based temperature & humidity monitoring node. Transmits data via 433MHz radio to an emonBase or emonPi.


ACAC Voltage sensor: An AC-AC Voltage adapter, used for measuring AC Voltage safely. Used in conjunction with the AC current measurement to calculate power consumption accurately.