A stroboscope disk for 60 Hz mains and an Arduino program to produce 120 Hz pulses.

It is summer time, holiday time, vacation. But it is a rainy day. Time to handle a few loose ends. One of the loose ends are the comments on my previous post for the turntable speed adjustment helper.

Two issues popped up:
-  Why an Arduino?
-  Why not use 60 Hz?

Why use an Arduino with a LED?

Simply because I had the hardware in front of my nose as a leftover of another experiment. I could have searched the house for another useable light source, but this was easier. Together with a small power bank it becomes a mains independent hand held light source. Due to the 100% modulation, the picture is much clearer than with an ordinary tungsten lamp.

Why not use 60 Hz?

Because I live in an area with 50 Hz mains frequency and I wanted stroboscope disks that can be used with any appropriate light source.The accuracy of tuning is indeed better for 45 rpm and 60 Hz mains, but with 50 Hz mains the speed will be 45,11278195….. rpm. Still good enough.

For those who really need a stroboscope disk for 60 Hz mains (= 120 Hz pulse frequency) and are too lazy to create it themselves using the Galva program, a pdf of such a disk is made available here. Also an Arduino program to produce a 119,9976… Hz pulse is available. For an exact 120 Hz pulse a crystal with a frequency containing the factor 3 is needed, e.g. 6, 12 or 15 MHz. But keeping in mind that the crystal frequency may not be exact 16 MHz, I do believe a pulse frequency of officially 119,9976… Hz is good enough.

august 2023