Glen Akins has married the worlds of USB and World War II-era aircraft instrumentation, by converting an indicator originally used to monitor cowl flap positions for notifications from a modern PC.
"This indicator is a General Electric model 8DJ4PBV DC Selsyn indicator. It is one of about 50 different varieties of General Electric DC Selsyn indicators," Akins writes by way of introduction to the project. "These indicators were commonly used on US and UK military aircraft employing DC electrical systems during the WWII era in the 1940s. Their operation manual states these indicators were used to give the pilot a 'visual indication of the position of landing wheels, landing flaps, cowl flaps, oil cooler flags, or similar movable parts of the airplane structure.'"
That's all well and good if you've got a WWII-era aircraft to monitor, but Akins does not — yet, at least. Thus was born a project to convert the device for use as a general-purpose indicator — talking to a .NET Windows application over a USB connection. That's perhaps not as easy at it sounds: the indicator is neither electronic nor directly driveable from something as simple as voltage, being based instead on Selsyn technology — a form of synchro.
The conversion board Akins developed for the project is based on a Microchip PIC16F1459 microcontroller and four MCP31HV41-502 digital potentiometers — one for each of the cowl flap indicator needles on the display, which was retrieved from a scrapped four-engine aircraft.
"The connection to the meter is made using an Amphenol MS3106A16S-1S connector," Akins writes — with a USB Type-C connector at the board's other end for the PC link. A 24V power supply, meanwhile, provides the grunt required to push the needles against their snap-to-fault springs.
Akins has promised to release the board design files and source code for both the PIC microcontroller and the Windows application to drive the indicators on the project's GitHub repository, though at the time of writing the repository had not yet been made public. More information is available on Akins' website.