You already know how a strobe pattern on a turntable appears to stand still. But what if the pattern wasn't printed — what if it was the light source itself? The ring of light on this PCB is that answer.

Drop the 100 mm disc onto your platter, flick the slide switch to 33⅓ or 45, 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.

HOW IT WORKS
A crystal resonator provides a precise clock, which passes through a divider chain to drive LEDs positioned at the correct intervals for each speed. No calibration — the accuracy comes from the crystal, not from software.

WHY THIS IS COOL
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.