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emonTx V3 - Electricity Monitoring Transmitter

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  • CT sensors and AC-AC adapters NOT included - can be purchased separately
  • emonTx V3.4 PCB
  • Wall-mount clip
  • DS18B20 on RJ45 temperature sensor connection
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£60.00 (inc VAT) £50.00 (exc VAT)
300.00 Grams
Calculated at checkout

The emonTx V3.4 is a low power wireless energy monitoring node designed for monitoring AC electrical power on (up to) 4 separate (household/building) circuits using non-invasive clip-on CT current sensors and an AC-AC Voltage adapter to provide a voltage signal for full Real Power calculations and AC VRMS readings.

The emonTx is designed to be used in conjunction with an emonPi or emonBase web-connected base-station to post data online to Emoncms.org and/or log data locally to the Raspberry Pi's SD card. Alternatively it is possible to add WIFI directly to the EmonTx with a ESP8266 WIFI adapter.


To get started visit the OpenEnergyMonitor Setup Guide.


Required for Operation

  • One or more clip-on CT sensor(s)
  • 9V AC-AC adapter power supply (UK Plug), (Euro Plug) or (US Plug) - enables accurate Real Power measurements. (Alternatively 3 x AA batteries / 5V DC USB Mini-B Power Supply can be used for less accurate Apparent Power measurements.)



  • Measure AC Apparent Power, AC Real power* and AC VRMS voltage (when AC-AC voltage adapter is connected)
  • 3 x single-phase CT current sensor inputs (100A / 24KW @ 240V max)
  • 1 x high sensitivity single-phase CT current sensor input channel (18.8A / 4.5KW @ 240V max)
  • 1 x RJ45 I/O - connect chain of DS18B20 temperature sensors and pulse counting IRQ sensor
  • Terminal block access to power rails, digital and analogue I/O, IRQ port and PWM for connecting pulse counting sensor / DS18B20 temperature / Aux sensors
  • Single AC-AC adapter can power the unit and provide AC voltage measurement
  • An on-board 3x AA battery option with remote monitoring of battery voltage 
  • RFM69CW 433Mhz Low Power RF Module with SMA antenna
  • DIP switch selection of RF node ID and 240V/110V AC adapter calibration selection
  • Arduino compatible ATmega328 8-bit microprocessor
  • Aluminium wall mount enclosure with recycled acrylic fascia
  • CE Certified
  • Made in UK with RoHS components free of conflict materials
  • The unit is manufactured and assembled with care in the UK.


Includes (as standard)

  • emonTx V3.4 PCB fully assembled
  • On-board 3 x AA Battery Holder
  • SMA Antenna 
  • Aluminium enclosure & custom fascia - assembled
  • Firmware uploaded and tested


Does Not Include (as standard)


Note: CT sensors give a much better reading of instantaneous power than pulse counting, we recommend using a CT whenever possible. When monitoring power using pulse counting method from a utility meter the sample rate is limited to the number of pulses, at low power values the interval between pulses can be extremely long.


RF Node ID

Multiple emonTx unit's can operate on a single RF network posting to a single emonPi / emonBase web-connected base station (Raspberry Pi + RFM69Pi), each emonTx on the same network must have an unique node ID. The nodeID can be selected at time of purchase or set using the on-board DIP switch to toggle. If more than two emonTx's are required on the same network then further nodeID values can be set via RF node ID serial config.  



The emonTx is Arduino compatible: updated/customised firmware sketches can be uploaded using Arduino IDE and a USB to UART cable (available separately)

The emonTx comes pre-loaded with the Discrete Sampling firmware for single phase operation, however alternate customised firmware sketches and be easily uploaded from the PlatformIO / Arduino IDE and a USB to UART cable (not included).

Firmware repositories:


Note: even though the unit is ready programmed we recommend a USB to UART cable to keep at hand for debugging and updating / customising firmware using Arduino IDE.




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