emonTx TH V1.5
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 RFM69Pi) which then posts the data to an emonCMS server (e.g. http://emoncms.org) for logging, processing and graphing. The 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 Humidity sensing options - Using DHT22 temperature and humidity sensor, or if humidity is not required just a DS18B20 temperature sensor. Both DHT22 and DS18B20 can be used together as shown above for internal and external readings.
- 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.
- Update: the emonTH now supports multiple DS18B20's, see blog post
- New V1.5: Node ID select DIP switch: Set up to four unique node ID's via on-board DIP switch
- Microcontroller: ATmega328 @ 3.3V
- 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: RFM69CW (RFM12B can also be used)
- Battery life: 1-3 years expected, see blog post
- On-board LTC3525-3.3 DC-DC boost converter see emonTH hardware blog post
|Arduino||ATmega328 Port||Special Function||emonTH V1.5|
|Analog 0 (D14)||PC0|
|Analog 1 (D15)||PC1||2x AA Battery Voltage|
|Analog 2 (D16)||PC2|
|Analog 3 (D17)||PC3|
|Analog 4 (D18)||PC4||(SDA)||DHT22 Data|
|Analog 5 (D19)||PC5||(SCL)||DS18B20 One-wire Data|
|Analog 6 (D20)|
|Analog 7 (D21)|
|Digital 0||PD0||(RXD)||FTDI Tx|
|Digital 1||PD1||(TXD)||FTDI Rx|
|Digital 2||PD2||(int0) PWM||RFM12B IRQ|
|Digital 3||PD3||(int1) PWM||Terminal block|
|Digital 5||PD5||PWM||DS18B20 PWR|
|Digital 6||PD6||PWM||DHT22 PWR|
|Digital 7||PD7||DIP 1|
|Digital 8||PB0||DIP 2|
|Digital 10||PB2||(SS) PWM||RFM12B SEL|
|Digital 11||PB3||(MOSI) PWM||RFM12 SDI|
|Digital 12||PB4||(MISO)||RFM12 SDO|
|Digital 13||PB5||(SCK)||RFM12 SCK|
See getting started with the emonTH: Getting started with the emonTH
DIP Switch node ID
New for emonTH V1.5: On-board DIP switch enables 4 RF node IDs to be selected by changing the switch positions. This will enable up to four emonTHs to be configured for use with a single emonBase / emonPi without the need to change the firmware (as before). Up to 30 emonTHs can theoretically connect to a single emonBase / emonPi. A USB to UART cable and Arduino IDE can be used to set additional unique node IDs by changing the nodeID variable at the beginning of the sketch. Alternatively, we are happy to set the node ID for you, before shipping. (Leave us a note with your order)
|DIP 1||DIP 2||RF node ID V1.x firmware||RF node ID V2.x firmware|
|OFF||OFF||19 (default)||23 (default)|
DHT22 Temperature and 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 to ~80Celsius
- Accuracy: humidity +-2%RH(Max +-5%RH); temperature <+-0.5Celsius
- Resolution: 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
DS18B20 Temperature Sensor
- Power supply range: 3.0V to 5.5V
- Accuracy over the range of -10°C to +85°C: ±0.5°C.
- Storage temperature range:-55°C to +125°C (-67°F to +257°F)
RFM69CW RF module (default 433Mhz) is used to transmit data to emonBase (Raspberry Pi + RFM12Pi) or emonPi. The JeeLabs JeeLib Arduino library is used as the driver for the RFM69CW module. In JeeLabs packet format.
External DS18B20 Temperature Sensor Connections
Only one DS18B20 sensor can be connected to an emonTH, if a DHT22 sensor is detected it's assumed the DS18B20 is external. If more than one DS18B20 is required see emonTH alternative firmware.
Black - GND
Red - Dig 5 (digital I/O used as sensor power pin to enable sensor switch off in between readings to save power)
White - ADC5 (dig 18) one-wire bus
Pulse Sensor Connection
|Screw terminal pin||Connection|
|2||3.3V - Red|
|3||GND - Black|
|4||IRQ 1 / Dig3 - Blue|
See blog posts:
By default, the emonTH is shipped without an SMT mini-B USB connector since the standard case does not allow use of the USB port to power the emonTH. However, a community-contributed 3D printable case design, which does allow use of the USB connector, is available at: http://www.thingiverse.com/thing:365035
Arduino compatible, a UART to USB cable is required to upload code
Open-Hardware Design Files
All the Design files for the emonTH are hosted on GitHub, see: https://github.com/openenergymonitor/Hardware/tree/master/emonTH/emonTH_V1_5
Proudly open source
The hardware designs (schematics and CAD files) are licensed under a Creative Commons Attribution-ShareAlike 3.0 Unported License.
The firmware is released under the GNU GPL V3 license
The documentation is subject to GNU Free Documentation License
The hardware designs follow the terms of the OSHW (Open-source hardware) Statement of Principles 1.0.
Environmental & Life Cycle
We are passionate about sustainability and are aware of the embodied energy and use of resources involved in electronic manufacture. We try our best to reduce environmental impact wherever possible:
- We have recently been inspired by a few projects taking a lead in promoting and making steps towards Ethical and Sustainable Electronics, see our blog post we wrote on the topic .
- The PCB's are manufactured in the UK by a manufacturer who uses lead free techniques, complies to the highest environmental industry standard and is actively investing in techniques and equipment to reduce waste and minimize environmental impact (e.g water treatment and recycling). Hot-air leveling was chosen instead of immersion gold finish to reduce environmental impact.
- Assembly is done in the UK. All components are RoHS compliant and free of conflict materials.
- Surface freight is used in preference to air shipping when ordering parts in bulk. This consumes 33 times less energy.
- We have strived to optimise electrical consumption in our hardware to be as low was possible and recommend the use of green, rechargable batteries, see blog post
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