TW39 to Double Current with FSG System

[G8LHS]

Been working away on this project for some time now - on and off for the past 5 years..

Had a burst of enthusiasm between Christmas and the New Year, and wanted to actually get on and build something useful, so here is the progress so far

Telex Control Unit.jpeg

Concept works like this:

TW39 level input and is controlled by the simple FSG as published here by Horatius - this takes care of the motor control and keeping I-Telex happy.

The output of this is then fed into an electronic Polar Relay, via optocoupler isolation.

The Polar Relay takes care of the conversion from Single Current to Double Current - A pair of generously rated transistors switch the output between +/- supply as needed.

All of this is on the upper board in the picture.

The lower board is the power supply, and also houses the switching relay for power to the machine.

There are two versions currently in build/test - One to suit the English machines, and one to suit French machines - all are Double Current, and 20mA loop, but the French machines prefer a lower voltage of around 48V.

Still plenty to do, but theres progress....