Hi everyone!
this project started because I was tired of replacing coin cell batteries in my Zigbee sensors. Ikea is one of the few manufacturers who don’t use disposable cells, but they didn’t offer a temperature / humidity sensor. So I ended up designing my own hardware from scratch. My sensor is powered by a single AAA cell, boosting its voltage to 2.2V internally. An nRF52840 is used as the microcontroller and Zigbee radio. Because there was some room left on the board, I also added a magnetic contact sensor and recently an illuminance sensor. The nRF52 has some really neat power saving tricks, so I managed to reduce the power draw to an average of around 17uW. A rechargable AAA cell should last for many months.
Writing the firmware was more difficult than I had anticipated. I thought that a simple sensor like this had been done a hundred times before. But Nordic does not offer a lot of examples and there are only very few open-source projects. Zigbee itself has a bit of a learning curve with its clusters and limited debugging. But somehow I managed to get it to work. The device is natively compatible with the home assistant zigbee add-on and works with Zigbee2MQTT as well (using a custom converter).
I have been using these sensors for a few months and they do work quite well. There is a more detailed writeup of the project on its Hackaday page: Zicada - DIY Zigbee Multisensor | Hackaday.io
All the hardware and software files are available open source on GitHub: GitHub - CoretechR/Zicada: DIY Zigbee Multisensor · GitHub
You can use these files to build you own Zicada sensor. The device itself is not too expensive (around 15€ in parts) but you need a few tools for assembling and programming it so it’s a bit of an investment if you only need a few devices. Also, I am still testing these and the software might not be perfectly stable.