Yeah, the laser shines against the mirror which is glued to a tiny wedge of wood (so the reflection will be eccentric but not really needed I learned since you can just stick the motor axel into the eraser at an offset angle to adjust the circle diameter) and then the eraser that sticks on the motor axel. As the motor spins it counts the time between each time the IR interrupt sensor (at the bottom of the motor axel) makes a full rotation. Then it divides that number by 60 to see how long to wait in between each second before turning the laser pin on briefly (the longer it’s on the more stretched out the “second” segment, which is how I highlight the minute and hour and current second). It basically self-adjusts to whatever amount of time has expired in between each full rotation. If you slow the motor down by rubbing on the axel slightly it still self-corrects and just displays each second “segment” at a lower resolution the less time it has to spend on each.

It’s a really interesting project and I’ve learned a lot from some of the undexpected charactersistics it has like being able to be slowered down and still display 60 “seconds” (as long as there’s some minimal amount of time, like 2ms each). There is also a microsecond offset that always applied to the whole timing that used to adjust it so that 12:00 is straight up and down.

It works but it’s really faint. I can see it easily if it’s shining against the wall next to my table where I’m working on it but for larger distances like in the video it’s not bright at all without the lights off.

And lasers are hard as crap to film I’m discovering. You get that barber-pole effect where the harmonic of the refresh rate and the recorded fps phase in and out. Like your car blinker and the blinker on the car in front of you kinda thing…

Thanks!