b-parasite

b-parasite is an open source soil moisture and ambient temperature/humidity/light sensor.

Features

• Capacitive Soil moisture sensor - see this blog post, this Twitter thread, and this post for nice resources on how they work
• Air temperature and humidity sensor using a Sensirion's SHTC3
• Light sensor using an ALS-PT19 phototransistor
• Powered by a common CR2032 coin cell, potentially for over two years
• Support for nRF52840 and nRF52833 modules
• Open hardware and open source design

Software

This repository also hosts a few different firmware samples for b-parasite.

Sample	Description	Extra Documentation
samples/ble	This is the most battle-tested and useful firmware. It periodically reads all sensors and broadcast them via Bluetooth Low Energy (BLE). It works with Home Assistant + BTHome out of the box.	Docs
samples/zigbee	An experimental/educational/exploratory basic Zigbee sample built on nRF Connect + ZBOSS. It integrates with Home Assistant via ZHA or Zigbee2MQTT.	Docs
samples/blinky	The classic "Hello, world"	-
samples/soil-read-loop	Reads the soil moisture sensor on a loop. Useful for experimenting and calibrating the sensor.	-
samples/input	Handles button presses. Useful for power profiling GPIO interrupts and testing debouncing for push switches on boards that have them.	-

Documentation

Information about how to order, assemble, build the samples, protect the sensor and flash the firmware is on the Wiki.

Repository Organization

• code/ - A west workspace containing the common prstlib module library and samples, built with Nordic's nRF Connect SDK.
• kicad/ - KiCad schematic, layout and fabrication files for the printed circuit board (PCB)
• data/ - data for testing and sensor calibration
• bridge/ - an ESPHome-based BLE-MQTT bridge
• case/ - a 3D printable case

Case

We have three different 3D-printable cases:

1. Original snap-on case - case/Top.stl, case/Bottom.stl
2. High airflow - case/b_parasite_case_high_airflow.stl
3. Mushroom-style - available on Printables
4. b-parasite Hat - available on Printables

Accessories

Designs and hardware to help you, when building your own:

1. Desk holder for b-parasites Printables

License

The hardware and associated design files are released under the Creative Commons CC BY-SA 4.0 license. The code is released under the MIT license.