Elehobica's LED Stroboscope Is Music to Your Ears for Vinyl Turntable Tuning
Card disc and bulky strobe light? No, just a single ring of LEDs and some accurate timing.
Pseudonymous maker "Elehobica" has designed a tool that uses persistence of vision to check if your vinyl turntable is rotating at the right speed — without the need for an external stroboscope.
"You already know how a strobe pattern on a turntable appears to stand still. But what if it was the light source itself instead of the printed pattern? The ring of light on this PCB is that answer," the maker explains. "Drop the 100mm disc onto your platter, flick the slide switch to 33⅓ or 45 [revolutions per minute], and a ring of green LEDs starts flashing at a crystal-locked frequency. If the dot pattern stands still, you're golden. If it drifts, time to reach for the speed trim pot."
The rotational speed of a turntable is important: too fast or too slow, and it will shift the pitch of the music to match. Traditionally, the way to check is with a stroboscope: a printed card disc with black and white markings is placed in the center and the turntable activated, then a strobe light flashes at a rate which should match the spinning of the disc. If all is right, the black and white strips appear static; otherwise, they'll appear to be slowly spinning.
Elehobica's LED version does away with the need for a strobe, putting everything on one circular PCB. "A crystal resonator provides a precise clock, which passes through a divider chain to drive LEDs positioned at the correct intervals for each speed," the maker explains. "Unlike a printed strobe disc, not every position on the ring has an LED. But take a look at the spinning disc — you'll see a continuous, periodic ring of dots even where no LEDs exist. That's persistence of vision doing its magic."
More information on the project is available on Hackaday.io; Elehobica is selling assembled units on Etsy at $35 plus shipping.