Hardware

Building Electromechanical Displays

Countdown clock

With the removal of Philly’s 30th street station Solari split-flap display putting mechanical signage back in the news I thought it was a good time to revisit my countdown project and share some resources.

Here’s my original post about the STEAM Carnival Countdown Clock. We went with Alfa-Zeta 18″ seven segment modules which were ~$150 each. You can go larger at 25″ but the price jumps to ~$350 and it requires 36V instead of the 24V of the rest of the line. For every 7-segment module you need to spend $57 on the control module. That part is definitely worth the money; unless you’re attempting something high framerate or rhythmic where you’d need direct drive, the prebuilt RS-485 controllers are a huge time save.

Alfa-Zeta also sells flip-dot displays like the ones pictured above. A 7×7 dot display with 1/2″ dots is 3-3/4″ tall/wide and costs ~$92. They make larger 14×28 modules, 7-1/2″x15″, that are $480. I don’t think I’d approach a new project using flip-dots that wasn’t using someone else’s money and even then I’d balk.

Of course the alternative to this is getting salvaged flip-dot displays. Rollsign Gallery seems to be the the most comprehensive resource for acquiring old flip-dot displays taken from transit vehicles. For a 41″ long 7×90 dot display from the side of a bus, you’ll pay a little over $300 shipped. hshutan has a project for interfacing with these flip-dot signs using RS-485. Although not listed, they also have some raw flip-dot modules that you could build into a display for <$130 each. You'd need to build your own controller though as hshutan did in an earlier project which is no small task.

We’ve actually got 12 7-segment digits now idling at work that should be put back into service. Let me know if you do any cool electromechanical signage projects!

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