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emonTx V3.4

The emonTx V3.4 is the latest generation of the open-source hardware Arduino compatiable emonTx low power wireless energy monitoring node. The unit has been totally re-designed using surface mount (SMT) electronics to enable automated pre-assembled manufacture here in the UK.

Hardware change log

V3.4.5 (un-released)


  • Update R13 & R14 from 1% to 0.1%/0.5% tolerance

V3.4.4 (un-released)

Minor PCB changes:

  • fix overlayed double via
  • Add protection ring for top-right fiducial


Shipping March/April 2018 onwards

  • Identifiable with blue CT4 jackplug socket (mostly)
  • Add extra UART header with Rx/Tx swap-over for easy ESP connection
  • Increase reservoir capacitor of AC-DC circuit C18 16uF to 100uF to allow for greater peak power consumption of RFM69CW (compared to RFM12B)
  • Change Burden resistors R7, R8, R9 (22R) from 1% to 0.5% tolerance to increase accuracy. Wanted to change to 0.1% but unable to source
  • Changed Burden resistor R18 (120R) from 1 % to 0.1%
  • Change all 470K resistors from 1% to 0.1% (R1, R2, R4, R6, R11, R12, R15, R17, R21, R23, R27, R30)
  • Changed CT4 jack plug socket to blue colour to indicate low power high accuracy channel

Live BOM:


Aug 2016

  • Same BOM as V3.4.1
  • Increase mini USB location pin holes from 0.8mm to 0.9mm

3.4.1 Mar 2015

  • lots of via GND links around GND plane - make sure ant has best GND plane possible
  • make sure antenna has got GND plane under ant PCB trace
  • pull top gnd plane in around RFM69CW module and rear GND plan to cover whole undersided
  • Get rid of unused L1
  • Move D2 location to not be under battery holder
  • Correct terminal block silkscreen
  • Disconnect RJ45 pin 1 and 3 from GND, stop power rail short if ethernet cable is connected by mistake


  • More FTDI connection bit to the left
  • Increase pads for DIP switch
  • Add TVS diodes, CT input protection


  • ATmega328 on-board
  • Edge SMA Antenna
  • Non plate through mounting pads to eliminate interference through enclosure
  • RJ45 DS18B20 temperature sensor
  • 3 x AA Battery monitor on ADC7
  • DIP Switch on Dig8 and Dig9 for Node ID selection
  • RFM69CW compatible with SEL line pull-up resistor
  • Pulse counting / terminal block IRQ changed from D2 IRQ0 to D3 IRQ1 since RFM12B now uses IRQ0
  • Changed MCP1700 3.3V regulator to MCP1702 3.3V regulator to allow for powering from higher voltages (12V max) over RJ45








See Hardware Wiki Documentation for further technical documentation regarding emonTx.

Open Hardware

Hardware designs (schematics and CAD) files are licensed under the Creative Commons Attribution-ShareAlike 3.0 Unported License and follow the terms of the OSHW (Open-source hardware) Statement of Principles 1.0.

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