AnalogFrequency by TMRh20 2016
Simple code to detect the frequency and amplitude of AC waveforms represented as a DC signal.
Designed and tested with HB-100 Microwave Doppler Radar modules: http://tmrh20.blogspot.com/2016/06/hb-100-gh1420-10.html
See the included examples for usage.
Also https://hackaday.io/project/371-hb100-radar-shield for the pre-amp circuit.