A Clock Built From a Resurrected Flip Dot Display

Electromechanical displays, such as flip dot displays, used to be very common in the days before LEDs and LCDs. Flip dot displays are made up of a matrix of “pixels” that can be switched between a light or dark color. Those pixels are actually small hinged mechanisms the can be flipped open or closed. The insides are painted a bright color, so opening the mechanism makes that dot visible. Something like an electromagnet coil is usually used to flip the mechanism. Mark was able to get his hands on a vintage flip dot display, and brought it back to life as a very cool clock.

Mark built this clock back in 2015 after purchasing his flip dot display from Rollsign Gallery. The display was well-used, and most likely came from a bus or train station — or maybe even the bus or train itself. It has a total of 175 dots arranged in a 25 x 7 matrix. All of the mechanisms were in working condition when Mark got the display, but there wasn’t any controller to activate them. His first step was to reverse-engineer how the dots are flipped. It turns out they work a bit like an LED matrix, and 9V pulses need to be sent to the columns while the rows are held either high or low in order to flip a specific dot open or closed.

After figuring that out, Mark was able to build a controller board using a Microchip PIC16F microcontroller and MIC5821 sink drivers paired with MIC5891 source drivers. A DS1307 RTC keeps track of the time, and has a battery backup to continue working through power outages. Those are soldered to a homemade single-sided PCB. The PIC16F was programmed with Microchip’s MPASM assembly language IDE. The board can display the time in different modes and at different sizes, and changes are always made only to the necessary dots in order to save on refresh times. The display was housed within an enclosure that was cut out of oak on a CNC router, so it looks nice on display.