I needed a couple of motions sensors to automate lighting in hallways and other rooms. Since the lights should only turn on when it is dark, the system also needs to know the ambient light level in the location where the motion was detected – so I added a simple brightness sensor to each node.
This is based on the MySensors RF framework, it uses an Arduino Pro Mini clone, it is low power (runs for >18 months one a pair of AA batteries) and low cost (cost of materials <EUR 10 ).
Source code and schematics are available in Github, and a more detailed description here.
I build a ESP based water flow sensor that transmits water volume and an ON signal when the shower is used so that the bathroom light stays on due to room occupancy (via ESPNow).
Runs with a lifepo battery directly connected to pins and wakes up every 3 minutes to check on water flow, rest is deep sleep.