The emonTx4 is part of the AVR-DB based hardware family which now includes the emonPi2 and soon to be released emonTx5. While no longer available in the shop the emonTx4 is still actively supported as part of the latest generation of hardware.

These units provide a redesigned focus on higher accuracy, more CT channels and precision voltage sensing. When combined with the emonVs voltage sensor, the emonBase base-station and a selection of CT sensors, the emonTx4 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.