The Energy Monitor Temperature Humidity 3 (emonTH3) is an ultra low power temperature and humidity monitoring node with support for pulse counting and additional external temperature sensors.
It is an update to the OpenEnergyMonitor emonTH2 with the following goals:
- Increase the battery life from the current ~4 years on 2xAA
- Update the components
- Reduce the overall cost of the system
- Provide user expansion for other sensors
It should be used with the emonTH-fw firmware.
The microcontroller can be flashed using a Raspberry Pi and OpenOCD. This allows end users to update the emonTH3's firmware without a specialised Cortex-M debugger. The following steps are used to do this:
Warning
The emonTH3 must be powered by the +3V3 supply provided by the Raspberry Pi while it is being programmed otherwise the microcontroller could be permanently damaged. The batteries must be removed before programming and the external supply removed before they are reinserted.
The board is designed using KiCAD version 7. The schematic and floorplan are provided as PDF files. If you want to render your own files, run ./generate.py. This produces Gerber files as well as KiCAD PCB and schematic files tagged with the git commit for traceability.
Note
The emonTH3 will be available fully assembled and programmed from the OpenEnergyMonitor shop in 2025.
Designing for ultra low power operation is very challenging and involves investigating every component and the whole system architecture. On the hardware side, the main considerations are:
- Leakage of high value capacitors.
- Idle current of all components.
These can be reported:
- as a GitHub issue
- on the OpenEnergyMonitor forums
As the hardware design flow doesn't quite follow as nicely as software, if you want to contribute a change, please raise an issue as described above and we can collaborate.
After cloning the repository, run ./install-hooks.sh to add the render on commit.
- Glyn Hudson and Trystan Lea @ OpenEnergyMonitor
- Gordon Davidson @ OpenEnergyMonitor Forums