From Glen Akins (@bikerglen):
In this project, I convert two panels from a vintage Grass Valley video switcher into general-purpose USB input and output devices without modifying the original panels. This project required both reverse engineering the hardware and deciphering the software protocols used to communicate with the panels. Because these panels required learning how to communicate with a microcontroller and a small FPGA, this project was significantly more challenging than the previous project where I converted a matrix button panel from the same mixer into a USB device.
In this write up, we’ll examine the two panels in detail and determine the hardware interface to the panels. Once the hardware interface is determined, we’ll build some boards to use to help decipher the protocols used to control the boards. Once the protocols are understood, we’ll build a second set of boards to control the panels using USB then develop the USB software and an example Linux application that controls the panels over USB. This project took about four months from start to completion.