I've released an updated version of this project.
The following features have been added:
A battery charger circuit that will charge NiCad or NiMh batteries.
A low battery warning and low battery shutdown option.
A switch or jumper to select low or high gain for the beat amplifier.
there were two schematics for the initial version.
Below are the schematics for the initial version.
Better accuracy with the optical sensor.
Higher sensitivity schematic.
More sensitivity to pick up beats from quiet ticking clocks. Only needed with sound or vibration sensors.
Download parts list for the initial version.
Questions or comments? Email me: