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The emonTx4 is the latest generation of OpenEnergyMonitor open source monitoring hardware, redesigned with a focus on higher accuracy, more CT channels, precision voltage sensing and a new microcontroller core. When combined with the new emonVs voltage sensor, the emonBase base-station and a selection of CT sensors, it provides an end-to-end electricity monitoring solution perfect for monitoring home consumption, solar generation, EV charging, heat pumps, battery storage or any AC electrical circuit for that matter.


Key features

  • 6x clip-on CT current sensor inputs (suitable for a range of 333mV voltage output CT sensors).

  • emonVs precision voltage sensor input.

  • Full Real/Active power measurement & continuous sampling.

  • Cumulative energy persisted on reboot.

  • The initial firmware release supports single phase monitoring only.

  • Support for 3 phase voltage sensing.

  • 3 pluggable terminal block inputs for DS18B20 temperature sensing, pulse counting or an analogue voltage input.

  • RJ45 socket for pulse counting and DS18B20 temperature sensors.

  • On-board USB to UART converter for easier programming and serial output.

  • 433 MHz radio transceiver

  • Extension header pins for use with ESP8266, ESP32, Pi Pico & Pi Zero development board extension modules

  • Wall-mount aluminium enclosure

Technical spec


We have taken several key steps to improve accuracy with the emonTx4. The largest source of improvement comes from: a higher accuracy voltage sensor, higher accuracy CT current sensors and a wider range of CT sensors with current ratings that can better suit the load being monitored (making sure the analog-to-digital range of the microcontroller is being put to full use).

The key sensor and component tolerances are now:

  • CT Sensors: ±0.5%

  • EmonVs voltage sensor: ±0.5%

  • Analog voltage reference ±0.2%

  • Combined: ±1.2%

We have also upgraded the microcontroller from the ATmega328 to and AVR128DB48. The main improvement is a higher resolution ADC at 12-bits (4x the resolution of the ATmega328) alongside the capability to monitor more channels.