CLOK Displays the Time on Flip-Dot Displays for Audible Satisfaction

Flip-dot displays are electromechanical devices that were commonly used before LED and LCD displays became affordable. Each pixel of a flip-dot display is actually a small disk that is flipped over using electromagnet coils. One side of the disk is almost always black, while the other side is a bright, high-contrast color like yellow, white, or red. Even though LEDs have made them largely obsolete, flip-dot displays still have a certain retro appeal — particularly because of the cool sounds they make as they flip. James Hutchby designed a clock that shows the time using just 28 of those flip-dots.

Most flip-dot clocks show time in the same way as you would on a LED matrix, with the numerical digits rendered by the pixels that are turned on. That looks nice and is easy to read, but it requires a relatively high number of pixels. CLOK instead shows the time more like an analog clock. Rows of flip-dots are arranged in a square pattern, and are flipped “on” in sequence to indicate the progression through either the day or an hour. It’s not clear where Hutchby sourced these flip-dots, but they came in 1x7 rows. Four of those form the square, with a one pixel overlapping at each corner. Some animations have been programmed to take advantage of the satisfying sound that the dots make as they flip.

Like most other flip-dots, these are flipped by swapping the current source and sink of an electric pulse. That means you’re essentially reversing the polarity between pulses — a job that H-bridge ICs are specifically designed for. Hutchby used a pair of L293D dual H-bridge chips for each row of flip-dots, for a total of eight chips. A Microchip PIC18F microcontroller is used for logic. All of those components are soldered onto a custom PCB. The result looks and sounds great, and we hope that Hutchby will provide some information on where he purchased his flip-dot displays, as they’re quite difficult to find these days.