December 8, 2022

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Reverse-Engineering A Display Protocol To Repair A Roland Synthesizer

An LCD mounted inside a Roland synthesizer

Restoring electronic gadgets isn’t as really hard as it applied to be. Thanks to the world wide web, it’s effortless to come across datasheets and software notes for any common part inside your gadget, and at the time you have identified the defective 1, you only purchase a substitution from a person of a million world-wide-web outlets — assuming you do not finish up with a fake, of study course. When it arrives to non-conventional parts, having said that, factors get additional difficult, as [dpeddi] observed out when a buddy requested him for aid in fixing a Roland Juno-G synthesizer with a broken display screen.

The key situation in this article was the truth that the display screen in dilemma was a customized layout, with no alternative or documentation obtainable. The only point [dpeddi] could figure out from the support manual was the basic pinout, which showed a parallel interface with two lines labelled “chip select” — an sign that the screen contained two different controllers. But the specific protocol and facts structure was not documented, so [dpeddi] brought out his logic analyzer to try and decode the signals created by the synthesizer.

Right after a little bit of trial and mistake, he was ready to figure out the protocol: it appeared like the display screen contained two KS0713-kind Liquid crystal display controllers, each managing one half of the display. Locating a suitable alternative was continue to proving difficult, so [dpeddi] determined as an alternative to decode the authentic alerts making use of a microcontroller and display the photo on a contemporary Lcd pushed by SPI. Right after some intial experiments with an ESP32, it turned out that the endeavor of looking through two moderately quick parallel buses and driving an even faster serial a person was a little bit too a lot for the ESP, so [dpeddi] upgraded to a Raspberry Pi Pico. This labored a take care of, and thanks to a 3D-printed mounting bracket, the new exhibit also fit snugly inside the Roland’s scenario.

The Pico’s code is available on [dpeddi]’s GitHub page, so if you’ve also obtained a dodgy display screen in your Juno-G you can merely down load it and use it to plug in a manufacturer-new screen. Having said that, the approach of reverse-engineering an existing exhibit protocol and translating it to that of a new a single is really common and need to occur in helpful when performing with any variety of digital machine: say, a vintage calculator or multimeter, or even yet another synthesizer.