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emonTx TH

EmonTH remoteDS18B20.JPG


The emonTH is an open-source, battery powered, Temperature and Humidity monitoring wireless node.

It's been designed to be an easy to deploy tool for monitoring building / room temperature and humidity.

The data from the emonTH is transmitted via wireless (433/868Mhz) to an emonBase web-connected base-station (we recommend a Raspberry Pi with an RFM12Pi) which then posts the data onto an emoncms server (e.g. emoncms.org) for logging, processing and graphing. The room temperature and humidity data can be used to inform a heating control system, feed into a building performance model or simply for general interest!


Temperature and Humdity sensing options - Using DHT22 temperature and humidity sensor, or if humidity is not required just a DS18B20 temperature sensor.

Easy to set-up - the unit comes pre-assembled and pre-loaded with Arduino compatible firmware. If desired the code can easily be changed by using an USB to UART cable and the Arduino IDE to upload a sketch of your choice onto the on-board ATmega328 microprocessor.

Long Battery Life - The emonTH is powered by two AA batteries through a high efficiency DC-DC boost converter circuit, taking a reading once every 60s the emonTH batteries should last for 1-3 years. We recommend rechargeable alkaline batteries for best performance and environmental impact (see blog post).

Expansion Options - If desired the emonTH function can easily be expanded: remote DS18B20 temperature sensors can be screwed into the terminal block for outdoor temperature monitoring, multiple DS18B20 temperature sensors can be connected at once on a digital one-wire bus.

An optical sensor can be added for interfacing with a pulse-output utility meter or a relay board could be connected for controlling an appliance.

Flexible choice of RF radio - Using the RFu328 with ATmega328 microprocessor as a common platform emonTH can work with either an RFM12B or Ciseco SRF RF radio


   Microcontroller: ATmega328 on RFu328 board
   Sensors: DHT22 (temperature & Humidity) / DS18B20 (temperature) sensor options
   Power: 2 x AA from on-board holder, LTC3525 3.3V DC-DC boost converter to extend battery life
   RF Radio: Using the RFu328 with ATmega328 as a common platform emonTH can work with either RFM12B or Ciseco SRF radio
   Battery life: 1-3 years expected, see blog post

DHT 22 Temperature & Humidity Sensor

   Power supply 3.3-6V DC
   Output signal digital signal via single-bus
   Sensing element Polymer capacitor
   Operating range humidity 0-100%RH; temperature -40~80Celsius
   Accuracy humidity +-2%RH(Max +-5%RH); temperature <+-0.5Celsius
   Resolution or sensitivity humidity 0.1%RH; temperature 0.1Celsius
   Repeatability humidity +-1%RH; temperature +-0.2Celsius
   Humidity hysteresis +-0.3%RH
   Long-term Stability +-0.5%RH/year
   Sensing period Average: 2s
   Independent sensor test report

Port Map

EmonTH V1.4 PortMap.png


See getting started with the emonth: Getting started with the EmonTH



RF Connectivity



Electrical Characteristics

power consumption, absolute max values


EmonTH Github repository

Open-Hardware Design Files

EmonTH V1.4 Schematic diagram PNG emonTH_V1.4_Sch.png EmonTH V1.4 Schematic diagram Eagle V1.4.sch emonTH_V1.4.sch EmonTH V1.4 Board files Eagle V1.4.sch emonTH_V1.4.brd


Environmental & Life Cycle