I'm planning a project that will involve driving four 7-segment flip-digit displays. These are electromechanical devices where each segment is either displayed or hidden depending on the direction of current flow through a coil. It looks like the best way to drive each segment is via an H bridge. Even though these are cheap and easy to use, and you can get two in a 16-pin package, that's still 14 packages, plus five packages of inverters, so I started thinking about multiplexing them.
In the attached drawing I show four coils (well, motors since that's what was used in the drawing I edited, but pretend they're just coils). If each coil corresponds to the same segment in each of the four digits, in principle I could get away with only four H bridge packages and two packages of inverters, if I could selectively interrupt the current at each of the red Xs, of which there would be 28 in the full circuit. Ironically, this approach would increase the number of required IO lines (the opposite of what multiplexing is usually used for), but drastically reduce the package count. The Xs could be relays, but that's a lot of relays, and I'd prefer something solid state for all the usual reasons. They can't be transistors since current has to flow both ways. Would triacs work? I've never used them before, but they ARE intended for bidirectional current flow, even if it's typically AC. I realize they stay latched until current stops flowing, but I can disable the H bridge to induce that. Any other possibilities?
In the attached drawing I show four coils (well, motors since that's what was used in the drawing I edited, but pretend they're just coils). If each coil corresponds to the same segment in each of the four digits, in principle I could get away with only four H bridge packages and two packages of inverters, if I could selectively interrupt the current at each of the red Xs, of which there would be 28 in the full circuit. Ironically, this approach would increase the number of required IO lines (the opposite of what multiplexing is usually used for), but drastically reduce the package count. The Xs could be relays, but that's a lot of relays, and I'd prefer something solid state for all the usual reasons. They can't be transistors since current has to flow both ways. Would triacs work? I've never used them before, but they ARE intended for bidirectional current flow, even if it's typically AC. I realize they stay latched until current stops flowing, but I can disable the H bridge to induce that. Any other possibilities?
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