System Overview

The OpenEnergyMonitor system has the capability to monitor electrical energy use / generation, temperature and humidity. It can also integrate with M-BUS and Modbus heat meters and other electricity meters for heat pump monitoring.

The units below 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


A 6 channel* electricity monitor with an integrated Raspberry Pi. Supports single or three-phase monitoring, wired temperature sensing & pulse counting. Can be used as a base-station to receive data from further 433Mhz radio nodes. Full local or remote data logging and visualisation capability via EmonCMS.


emonTx5 (available soon): A 6 channel* electricity monitoring node. Transmits data via 433MHz radio to an emonPi or emonBase. Great for expanding an emonPi2 monitoring setup where more CT inputs are required either in the same location or in a different part of the building.


emonTx4: The original 6 channel* energy monitoring node. While no longer available in the shop the emonTx4 is still actively supported under the current generation of AVR-DB hardware.


*Expand to 12 CT channels: Add a further 6 CT channels to the emonPi2 (Pi Zero 2W option only), emonTx5 or emonTx4 to monitor up to 12 circuits with an optional expansion board.

The emonTx4, emonPi2 and emonTx5 are all part of the same AVR-DB hardware family and share the same core electricity monitoring functionality including: 6x CT channel electricity monitoring as standard (expandable to 12 CT’s with an expansion board) and both single and full three phase voltage sensing support. The emonPi2 and the emonTx5 share the same measurement board, which is itself a minor evolution of the emonTx4 design, this is mostly a change of layout to support the integration of a RaspberryPi in the same enclosure for the emonPi2.


emonTH2: A battery powered, wireless, room based temperature & humidity monitoring node. Transmits data via 433MHz radio to an emonBase or emonPi.


emonBase: A Raspberry Pi base-station that receives data sent from an emonTx4/5 and emonTH radio nodes. Can be used instead of an emonPi2 where the installation favours locating these in different parts of a building. Hosts the emonCMS software for local data logging and visualisation.


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


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


Combined precision voltage sensor and power supply, sends voltage data and power to the emonPi2 and emonTx5 via RJ45.


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


Earlier hardware


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.


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.