Prop-based vehicle speed measurement
Not sure if this is of interest and/or has been done before, but...
After getting annoyed with vehicles speeding past our house, I have connected two Benewake TFS02 LiDAR sensors to a prop and pump the timing data to my PC.
One cog per LiDAR sensor, using FullDuplexSerial at 115 200 baud to take distance measurements at 500 Hz. They are basically being used as beam-break sensors without needing a reflector on the other side of the road; the distance readings also allow me to determine which lane the vehicle is in. The values of cnt at each "beam-break" event get passed to my PC via FullDuplexSerial at 9 600 baud and Excel does the maths. Because I know when the vehicle first 'broke the beam' and the last point it was still 'breaking the beam', I send the latter as well and can estimate the length of the vehicle.
Four data pins, four LEDs.
Parsimonious with RAM: