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This loop driver interfaces the TTL output and input on P2 of the Flesher TU-300 and TU-170A to a 60 mA
Teletype current loop. The circuit is in a small plastic case and plugs directly into P2 on the back of
the terminal unit. A cable with a 1/4 inch TRS connector leaves the other side of the unit. The sleeve
is not connected. The loop keying and sensing circuit is between the tip and ring of the connector. This
cable and be plugged into a loop, just the same as any other piece of equipment (such as a printer, reperf,
transmitter distributor, etc.).
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| The image at the right shows the PCB sitting in the bottom part of the plastic case. The plastic case is designed
to be a USB dongle, such as for a USB flash drive. The four pin Molex connector is larger than a USB A connector,
so the PCB is notched in to pass through the USB connector hole. The Molex connector is then mounted on the full
width PCB outside the case.
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| The image at the right shows a bottom view of the PCB in the case with the Molex connector. The Molex connector has
a plastic "hook" on each side that hooks around the edge of the board. However, the hooks run into the bottom of the
P2 hole in the TU cabinet. When installing the Molex connector, a small amount of super glue is put on the connector,
then the connector installed as designed (hooks around edge of board, pins through the four pads). Once the glue is
dry, the hooks are cut off flush with the bottom of the PCB using diagonal cutters. In addition, the connector pins
poking through the pads are cut off flush with the bottom of the PCB so they do not short to the TU cabinet.
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| A small notch was cut in the end of the top section to allow the cable to exit the box. The notch is triangular
and cut with two cuts with diagonal cutters. The notch has to be small enough to tightly grab the cable, but large
enough to allow the case to snap closed.
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