EmonTx V3

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emonTx V3

The emonTx V3 is the latest generation of the open source emonTx low power wireless energy monitoring node. The unit has been re-designed using surface mount (SMT) electronics to enable automated pre-assembled manufacture.


  • Emontx v3 can measure real power, apparent power, power factor, rms voltage and current on 4 different mains circuits, it also has inputs for temperature and humidity sensing.
  • Pre-assembled SMT design
  • A single AC-AC adapter can now be used to power the emonTxV3 and provide AC voltage measurement
  • 4x CT current sensing inputs
  • An on-board 3x AA battery option
  • Flexible choice of RF radio module and removable microcontroller

Port Map


Power Supply Options

Uploading Firmware

Start by downloading the firmware, libraries and setting up the Arduino programming environment by following this guide:

Setup the Arduino Programming environment

Once complete the emonTx firmware location should be navigable from within the Arduino IDE by going to:

File > Sketchbook > OpenEnergyMonitor > emonTxFirmware > emonTxV3

These are the examples available so far:


  • emonTxV3_RFM12B_DiscreteSampling
  • Examples:
    • emonTxV3_4chan_continuous
    • emonTxV3_CurrentOnly
    • emonTxV3_RealPower_Voltage


  • SRF___Low_Power___Current_only_Apparent_Power

The emontx firmware is available on github here: Github:emonTxFirmware

Standard Operation

CT Energy Monitoring

Single Phase



Extended Operation

Temperature Monitoring

Utility Meter Interface

Optical Pulse Counting

Direct Optical Interface

if you have an Elster meter (tested with Elster 100C) the emonTx V3 with an IR TSL261R sensor can be used to interface directly with the meter protocol to read off the exact accumulated watt hours that you have generated or used. This reading can be used on it's own or to cross-check and calibrate CT based measurement. See here for original blog post

RF Connectivity



Electrical Characteristics

power consumption, absolute max values

Open-Hardware Design Files

Proudly open source, the hardware designs are released under the Creative Commons Attribution-ShareAlike 3.0 Unported License:

Download Schematic PNG: emontx-v3.png

Download Schematic: emonTx V3.2.sch

Download Board files: emonTx V3.2.brd


Environmental & Life Cycle