Maker Michael P. has made it simpler so as to add some classic show aptitude to your subsequent mission — by reverse engineering basic Plessey GPD340 5×7 two-character bitmap show modules, so you do not have to.
“Final 12 months I got here throughout and acquired myself a bunch of those cute little shows,” Michael explains of the glowing DIP-format gadgets. “After fruitless makes an attempt to seek out any data on them, I made a decision to strive reverse engineer the pinout and driving scheme so as show one thing on them. This has turned out to achieve success.”
If you’ve acquired some undocumented Nineteen Eighties micro-LED shows at hand, there’s just one factor to do: reverse engineer them. (📷: Michael P.)
Developed by British electronics agency Plessey within the Nineteen Eighties to supply an easily-readable show for tools requiring a customized character set, every Plessey GPD340 module takes the type of two 5×7 LED matrices side-by-side in an DIP package deal. With simply eight pins to drive 70 particular person LEDs, although, it is clear that the components want one thing intelligent driving them — the one query: what?
“Given the low depend of pins (simply eight),” Michael explains, “it was assumed that the show has to make the most of some serial protocol to load pixel knowledge into inner registers. Thus, it ought to have not less than one serial clock enter and not less than one serial knowledge enter and the opposite pins might be chip-selects, output-enables, and so on.”
Preliminary makes an attempt to determine the controlling pins and format of the serial protocol by hand failed, so Michael constructed an automatic check rig powered by a Raspberry Pi Pico microcontroller board and a Texas Devices INA219 present sensor. “After a couple of minutes of operating, some random pixels on the GPD340 start to glow dimly,” Michael says, “which was signal.”
A profitable discovery of the pin-out and serial protocol means it is doable to re-use the show modules. (📷: Michael P.)
“Then,” the maker continues, “after a full run and evaluation of the collected present monitor log — it was clearly seen that mixture of pins brought on the present to surge. After that, it was very simple to see which pin is which. Additional determining the serial protocol was executed by guide experimenting on the identical breadboard.”
The result’s a pin-out and driving scheme, printed to GitHub beneath the permissive MIT license, which permits anybody to utilize the identical shows — even extending to a number of models, as Michael has confirmed with a six-module scrolling show.
Extra data is offered on Hackaday.io.