Previous Dot-Matrix Shows Give Up Their Serial Secrets and techniques

If there’s one factor we like higher round right here than outdated, obscure shows, it’s outdated, obscure shows with no documentation that want a wholesome dose of reverse engineering earlier than they are often put to make use of. These Plessey dot-matrix displays are an ideal instance of that.

We’re undecided the place [Michael] scored these shows, however they give the impression of being incredible. Every 8-pin DIP has two 5×7-matrix, high-visibility LED shows. They bear date codes from the late 80s below the half quantity, GPD340, however sadly, treasured little knowledge about them might be dredged up from the Interwebz. With 70 pixels and solely six pins after accounting for energy and floor, [Michael] figured there can be a serial protocol concerned, however which pins?

He determined to brute-force the method of finding them, utilizing a Pico to sequentially drive each mixture whereas monitoring the present used with a present sensor. This paid off after just a few minutes, revealing that every character of the show has its personal clock and knowledge pins. The protocol is easy: pull the clock and knowledge pins excessive then ship 35 bits, which the show types out and lights the corresponding pixels. The video under reveals a 12-character scrolling show in motion.

Plessey made plenty of shows for navy {hardware}, and these chunky little modules actually have a martial air about them. On condition that and the date code, these might need come from a Chilly Conflict-era little bit of navy {hardware}, like this Howitzer data display which sports activities one other Plessey-made show.

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