Yet another Hacker News

41 points blutack 1 day ago 6 comments

userbinator 1 hour ago | parent

The dots are so delicate, with tiny magnet wires and soft plastic that can melt, that it has to be done very carefully. Even with the very best desoldering equipment it would take forever.

Put a hot air gun on the back of the board, and they'll either just drop out or do so with a small poke of the pins.

bobek 1 hour ago | parent

I have recently resurrected one from an old bus — https://www.bobek.cz/buse/

amelius 23 minutes ago | parent

Instead of using capacitors ... why not use a negative supply rail? Then you can switch the direction of the current in a coil using only two transistors.

schobi 12 minutes ago | parent

It is still going to be many amps.

The capacitor circuit has the advantage that could can't mis-drive. If a transistor of the half bridge stays turned on for longer than the msec required, nothing will happen. The half bridge chip (usually) already prevents that both transistors are enabled at the same time. This is great when you develop firmware and might end up with one pin staying high for too long.

With a direct drive, the flip dort magnet wire could quickly burn through if you leave half an amp for too long.

amelius 7 minutes ago | parent

True, but you can program a controller such that this condition does not happen (modern microcontrollers have watchdog timers).

A bigger advantage of the capacitor approach is that you save power (though you could handle that centrally).

A downside of the capacitor approach is that capacitors can slowly leak, but for the application that does not matter much, I suppose. It just has to look nice.

schobi 18 minutes ago | parent

Summary: Mitxela designed and built circuit board to drive old flip dot displays - boards donated to Sam from Look Mum No Computer and iterating on an approach from Mike at Mike's Electric Stuff. He ended up with 1m^2 of flip dots with an interactive high frame rate fluid simulation.

I can only express my deep respect and recognition for an amazing execution, craftsmanship and video while creating some thing fun and entertaining.