Photons, Electrons, and Dirt

A Grass Valley Kalypso video switcher machine control panel (bottom) and crosspoint switch panel (upper right) after converting them into USB human interface devices using Silicon Labs EFM8UB2 USB microcontrollers.

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.

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The resurrected Grass Valley user definable switch panel.

In this project, I convert a set of illuminated push buttons from a vintage Grass Valley video mixer into a custom vendor-defined USB HID peripheral. Like the USB analog panel meters project, this project uses a Silicon Labs EFM8UB1 microcontroller for USB connectivity. Unlike the panel meters project which only received data from the USB host, this project needs to send data back to the USB host too.

In this write up, we’ll reverse engineer the button panel, decide on a strategy for reading the keys and controlling the LEDs, build a board, then write both embedded and Linux software to interface with the button panel. If you want to build your own device like this but don’t have this specific switch panel, don’t worry–the ideas presented here are applicable to any generic 3×4/4×3/4×4 matrix keypad with or without LEDs.

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The completed USB analog panel meters project.

I’ve always liked the way these little HUA SO-45 analog panel meters looked, but, given the long lead times from China, I’ve never ordered a set. This fall, I changed my mind and finally decided to order a set. While they were in transit to the United States, I designed a small board to control them over USB using a Silicon Labs EFM8UB1 Universal Bee 8051-baeed microcontroller.

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The finished wireless remote control for my Mopidy music server. Playback control and volume Icons by Icons by Darrin Loeliger (@MrNumma) and the Noun Project.

After wiring the house for a Dante digital audio network and building the Spotify and Pandora Wireless Remote Track / Artist / Album Display project, I decided the next thing needed to fix up my music listening experience was a quick way to change tracks, control playback, and adjust the volume without messing with a phone or web browser. The Wi-Fi connected Mopidy music server remote control was born!

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The completed music server remote track/artist/album display.

I use Pandora and Spotify a lot–typically from 7 in the morning until 11 at night. I got frustrated with the Spotify and Pandora apps on my Pixel 2 and their inability to find and control my Chromecast Audio players reliably. I also wanted a quick way to identify new songs or artists I heard without having to find my phone and open an app.

To solve these problems, I moved my music playing ecosystem to Linux and installed a wired Dante digital audio network for audio distribution. Finally I built a retro 14-segment, scrolling, always-on LED display that I could quickly glance at to discover what song was playing without having to find my phone and open an app.

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The completed RS-422 / RS-485 shield for the Automation Direct P1AM-100 open source PLC.

The RS-422 / RS-485 shield is an open source shield designed to add RS-422 and RS-485 communication capabilities to the ProductivityOpen family of open-source programmable logic controllers (PLC’s) from Automation Direct. It’s loosely based on the Arduino MKR RS-485 shield but updated to use an ADM2582E 3.3 V isolated RS-485 transceiver from Analog Devices. The completed shield fits inside the P1AM-PROTO prototyping enclosure.

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Inside my first add-on module for the P1AM-100 open source PLC. Two optically-isolated inputs, two relay outputs, a display, a half-duplex RS-485 transceiver, and a serial EEROM with a MAC address for the Ethernet module. The enclosure and headers are included in the P1AM-PROTO prototyping module. Not shown is the lid of the enclosure.

In January 2020, Automation Direct launched their ProductivityOpen family of open-source programmable logic controllers (PLC’s). The first controller in the series, the P1AM-100, is based on the Microchip ATSAMD21 microcontroller and programmed using the Arduino development environment. To encourage development, they launched a prototyping module alongside the controller. The prototyping module consists of a piece of perfboard, the required connectors, and a housing.

I was already familiar with Automation Direct and their PLC and pneumatic products after building my crate beast and zombie containment unit Halloween props a few years ago. I was intrigued by this new controller from a familiar company, the CPU selection, and the possibility of building my own modules that could tie in to the controller for future projects. I set out to build a couple of add-on modules but first needed to take a closer look at the controller and its available add-ons.

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