EmonTx Arduino Shield SMT





The emonTx Shield is an open source hardware Arduino shield footprint compatible electricity and temperature monitoring shield that can be connected to any standard Arduino UNO, Leonardo, NanodeRF (for web connectivity and posting to emoncms.org) or even the new Arduino Yun.


  • Apparent Power, Real Power*, Power Factor* and AC RMS voltage readings*
  • 4x Clip-on CT current sensing inputs
  • 1x AC-AC 9v Adapter input for AC voltage measurement and realpower calculation
  • 1x on board DS18B20 temperature sensor footprint
  • 2x DS18B20 terminals available via terminal block.
  • 433/868Mhz RFM12B / RFM69CW  (HopeRF) wireless transceiver to transmit/receive data to other OpenEnergyMonitor and JeeNode modules
  • Status LED

* with 9V AC adapter

Assembly of non SMT components

The board comes with all the SMT components the resistors, capacitors and LED already on the board. The non-smt components (the arduino headers, ftdi connector, CT and ACAC jack sockets) do not come pre-assembled and so a little soldering is still needed to complete the build of this board.

When assembling: The 3.5mm CT sockets and 2.1mm AC-AC Adapter socket needs to be soldered on the bottom of the PCB. (See the photograph above.) This slightly unconventional design was chosen to make a low profile design possible.

Soldering the RF Module

If you have chosen the option of an RF module this module will need to be soldered onto the board yourself. This is not as difficult as it may seem, start by adding solder to one of the corner pads of the PCB then move the RF module into place (taking care to orientate correctly!, see below) and then 'tack' the module in place by melting the solder on the corner pad as you adjust the final position of the module. If you have the RFM12B module the orientation of the module is marked on the PCB, just line up the RFM12B metal crystal with the outline on the PCB. As of Febuary 2015 we are starting to ship the new RFM69CW module wiith the emonTx shield. The RFM69CW should be soldered on in following orientation:

if your using the RFM12B make sure to set #define RF69_COMPAT 0 at the beginning of the sketch. See RFM69CW building block documentation for more info 

See Technical Wiki page for info on RFM12B / RFM69CW jumper settings, wiki page refers to the old 'thru-hole' design but the RFM12B operation and pin-out's have not changed. 

Open Hardware

The emontx shield is open hardware with the designs released under the Creative Commons Attribution 3.0 Unported License. The schematics and board files can be viewed and downloaded from the openenergymonitor github hardware repository here:

Firmware examples

EmonTx Shield Arduino example code can be found on github here:

Application examples

Further reading