Interfacing An Old Engine Cowl Flaps Indicator To USB

[Glen Akins] experienced a WW2-era aircraft engine cowl flap indicator lying about (as you do) and considered it would make a jolly good USB-connected indicator. The product in dilemma is a Basic Electrical design 8DJ4PBV DC Selsyn, which was meant for 4-engined aircraft. For these not familiar with the goal [Glen] explains in his in depth writeup, that piston-engine plane of that period were being air-cooled, and all through circumstances of utmost engine electrical power — these kinds of as during choose-off — flaps on the facet of the engine cowling could be opened to admit added cooling airflow. These indicator dials ended up linked to a sender device on each of the flap actuators, delivering the pilots an sign of the flaps’ positions.

The method of operation in the DC electrical power environment of WW2-era aircraft utilised the strategy of variable magnetic discipline orientation. The sender is a potentiometer, sending a voltage down the wire among 24V and ground. The indicator unit has a pair of coils set at 120 levels all around a ring, with the coils wired in collection, and the centre tap linked to the sender sign. The other ends of each and every coil hook up to the DC electricity bus so that as the sign voltage differs, the coils create a different magnetic area. Lower voltages bias the subject in the direction of the coil connected to 24V, and better voltages the other way. A long-lasting magnet in the heart is attached to the indicator dial, with a modest spring to bias it to the middle. A extremely very simple but productive arrangement, supplying analog feedback of the precise flap place.

To interface this detail to contemporary know-how, a personalized PCB was constructed leveraging the USB functionality of the PIC16F1459 microcontroller, that [Glen] was already familiar with. Four Microchip MCP31HV41-502 electronic potentiometers ended up pressed into services instantly driving the coils of the indicator models. That may seem like an odd if not viable way to drive such a thing, but [Glen] goes into some substantial concept and some modeling to figure out which gadgets would have sufficient margin, which is worth a examine for the unfamiliar. Immediately after little bit-banging the SPI relationship to the digipots (even while the PIC has hardware SPI) [Glen] goes on to describe how the USB endpoints function, ending off with a .Web application to drive it all.

We’ve found a great deal of hacks bringing retro hardware back again to life, connecting to fashionable computing. Here’s a job that goes the other way, building custom made aircraft instrumentation from modern day areas.

Jennifer R. Kelley

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