LED matrix displays and flat-screen monitors have largely supplanted old-school electromechanical models for public signage. We think that’s a shame, but it’s also a boon for the tinkerer, as old displays can be had for a song these days in the online markets.
Such was the case for [John Whittington] and his flip-dot display salvaged from an old bus. He wanted to put the old sign back to work, but without a decent driver, he did what one does in these situations — he tore it down and reverse engineered the thing. Like most such displays, his Hannover Display 7 x 56-pixel flip-dot sign is electromechanically interesting; each pixel is a card straddling the poles of a small electromagnet. Pulse the magnet and the card flips over, changing the pixel from black to fluorescent green. [John] used an existing driver for the sign and a logic analyzer to determine the protocol used by the internal electronics to drive the pixels, and came up with a much-improved method of sending characters and graphics. With a Raspberry Pi and power supply now resident inside the case, a web-based GUI lets him display messages easily. The video below has lots of details, and the code is freely available.
You may recall [John] from a recent edge-lit Nixie-like display. Looks like he’s got a thing for eye-catching displays, and we’re fine with that.
16 thoughts on “Flip-Dot Display Brought Out Of Retirement By New Drivers”
Just for the record : https://hackaday.io/project/18541-dot-flippers :-)
These have by far the best sound for any display. There was a store I used to pass on my daily trips like this. It got replaced with an LED board. Such a shame.
And you didn’t go in and ask for the old one?
Wonderful. Now I can put up my own “speed trap” sign next to the road.
I find it ironic that the flip dots look like little pacmans …
racka … racka
i service these displays for busses and a common fault report description is “pacman” this just means that the user interface shows dots running across the drivers interface display while it attempts to communicate with the display drivers
Can you get single dots for replacement service? I would like a couple of these but have never found a supplier.
Have a look at http://hannio.org/
This provides 7×5 dots for a reasonable price, new.
I bought “a few” more :D
The CPU is able to scan the array much faster than what you’re doing here; I guess you’re limited by the time required to flip over each dot. But do you need to be? What if you scan the array 1000 times a second, can you flip a dot using the many pulses from such a scan rate? How does an electromagnet respond to a PWM signal?
A solenoid act as a speaker if pwm frequency is audible. It can be mediated with some smoothing caps, but it is otherwise going to sing at 1KHZ.
Always wanted to get my hands on one of these, especially after attending a CCC and playing with the giant display MuCCC had there. Unfortunately being in Australia pretty much stymies any chance of me getting panels. I can dream though!
Really neat project. Thumbs up for effort and engineering!
By the way, several years ago I built my own flip-dot clock (http://paulius.bautrenas.lt/blog/flip-dot-clock) and had ideas about making it into a fully operational matrix display, as you did but never had time for that :/
That’s a beauty! Thanks for posting the link.
I was at Infocomm this past year and saw a company trying to bring back the flip dot display for large format signage….they had it hooked up to a kinect and it was doing real time replication of people walking past. By far my favorite thing at the show.
Just for fun, having the driver/controller emulate the classic hd44780 protocol and interface would open a lot of possibilities.
Some of the buses in the city I used to live in used these flip-dot displays on their signage along with 7-segment flip displays for the actual route numbers. The more modern buses in that same city (and pretty much everything I can think of in the place I live now) use LED displays. The LED displays are more efficient and otherwise better but the flip-dot displays are cooler :)
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