The instructions were to have at least 4 log posts. So here goes...

Everything is built on a breadboard. Schematics will come but only exists in my head for the moment. There is nothing that couldn't be deduced from the system design except perhaps for the revolution sensor that is darlington connected for amplification and fed into a comparator with hysteresis feedback. There is 3 unused comparators in that capsule so perhaps I will use one of them for conditioning the main sensor.

The main sensor isn't yet mounted in the head so I haven't been able to determine the viability of this project yet. Is the emitted laser light enough energy and in the right wavelength to get a retro reflex? Is the sensor sensitive or fast enough to detect the reflex?

Other things on the todo-list is to build a lock-detector for the PLL and only turn on the laser when the head is actually spinning (a tiny bit more eye friendly) and implement an app for the phone.

Another display solution could be to map detections onto a led ring that the user wears on the wrist as a watch.