Split-Flap Clock Uses Magnets Everywhere

A DIY split-flap clock in red, black, and white.

While split-flap alarm clocks once adorned heavy wood nightstands in strong numbers, today the displays are most commonly found in train stations and airports. Hey, at least they’re still around, right? Like many of us, [The Wrench] has always wanted to make one for themselves, but they actually got around to doing it.

A DIY split-flap clock and its magnetic base.This doesn’t seem like a beginner-friendly project, but [The Wrench] says they were a novice in 3D design and so used Tinkercad to design all the parts. After so many failures, they settled on a design for each unit that uses a spool to attach the flaps, which is turned by a stepper motor.

A small neodymium magnet embedded in the primary gear and a Hall effect sensor determine where the stepper motor is, and in turn, which number is displayed. Everything is handled by an Arduino Nano on a custom PCB.

Aside from the sleek, minimalist look, our favorite part is that [The Wrench] used even more magnets to connect each display segment to the base. You may have noticed that there are only three segments, because the hours are handled by a single display that has flaps for 10, 11, and 12. This makes things simpler and gives the clock an interesting look. Be sure to check out the build video after the break.

Want to build a more complicated clock? Try suspending sand digits in the air with persistence of vision.

2 thoughts on “Split-Flap Clock Uses Magnets Everywhere

  1. Cool, ,but just one step away from being perfect. Making use of a ESP8266, he would make time setting completely automatic.
    I have a split flap mechanism from an old alarm clock, that I intend to bring back to life in such way, one day when I will have time (haha, internal cry, knowing that day will never come)

  2. Old-fashioned split-flap clocks have a design that is fundamentally simpler than split-flaps from train and airport departure boards.
    The rightmost digits of clocks are directly and continuously driven by a clock mechanism with proper reduction, the top ends of each flap are held up until they dive under the edge of the tab holding them. This is not a precision mechanism and on the clock I have, minutes last anywhere from 48 to 64 seconds (yeah, I measured this). A tap on the clock can seriously shorten a minute, and there is no electronics nor feedback in the mechanism whatsoever, at least, in it’s simplest form.

    On the other hand, split flap departure boards are often solenoid-controlled, where one pulse allows exactly one flap to fall down. They are designed to rapidly advance say 50 flaps, then return to their “neutral” position, and they make heavy use of (electromechanical) sensors.

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