Hardware Details

  • Based on JeeNodeV5 design - many thanks to Jean-Claude Wippler for sharing his great work 
  • Compatible with most JeeNode shields
  • Designed to run on 3.3V and be powered by 2x AA batteries
  • Designed to fit in this case
  • Uses 3.5mm jack plug connections 
  • Can be powered using 5V via the mini-USB connector
  • Requires FTDI cable for programming 

Energy Monitoring 

‚ÄčNote: CT sensors give a much better reading of instantaneous power than pulse counting, we recommend using CTs whenever possible. When monitoring power using the pulse counting method, the sample rate is limited to the pulse rate. At low power values, the pulse rate can be extremely slow. 



  • Uses Hope Alpha RF / RFM12B Transceiver. Frequencies available include: ISM band 433Mhz (All countries), 868Mhz (Europe only), or 915 MHz (US and Australia only). The OpenEnergyMonitor kit includes the option of a 433Mhz or 868Mhz module. 
  • Up to 30 emonTxs can communicate with one emonBase station 
  • Potential for 250 different network groups set up in a single location 


The emonTx is designed to be powered by 2 x AA batteries or by 5v USB/FTDI. When powering the unit with 5V through the USB or FTDI header the on-board voltage regulator will reduce the voltage to 3.3V. The battery connection header is not regulated, therefore the max voltage at the battery header should should not exceed 3.3 Volts. If higher voltage is connected, the RFM12 is at risk of damage. The RFM12 can be operated at 5V, but that exceeds the recommended maximum.

emonTx was designed to consume as little power as possible. (Low power optimisation details are here) Much of the power optimisation can be done via software, e.g. putting the Atmega and RF12 to sleep when practical to do so. The following measurements were taken with two CT channels connected, but the software was reading from only one channel: 

0.1mA @ 3.13V =  0.31mW when Atmega and RF12 in sleep mode

6.7mA @ 3.13V = 21mW when ATmega is awake and RF12 is in sleep mode

7.14mA @ 3.13V = 22.35mW when ATmega and RF12 are awake but not transmitting

14mA (approx) @ 3.13V = 43.8mW when RF12 is transmitting - max power

Physical dimensions

Case: 102.8 mm x 61 mm

PCB: 63.3 mm x 56 mm