HW_ILoop_Power - fablab-wue/piTelex GitHub Wiki
Power for Current-Loop Interface
Historic Current Loop
... hand trimmed potentiometer for each line
TODO
All teletypes (with current loop interface) are designed for a current of 40mA. The receive unit (magnet coil) has a typical voltage drop of 15V. Taking into account the additional voltage drop in the interface circuits, a power supply voltage of about 20V should do - in theory.
BUT! The switching speed of a magnet coil depends directly on the intermediate circuit voltage - in this case the power supply voltage. On practical experience the intermediate circuit voltage should be at least twice the magnet coil voltage.
ADDITIONAL BUT! Most teletypes are used with a FSG (dialing device). This has also a relay in the current loop with an additional voltage drop. Some relay circuits (especially for "Wahlbereitschaft" = ready for dial) need a higher voltage (60V) to work as expected.
Hands-on tests
Working supply voltages with interfaces above:
Teletypes without FSG
Teletype | Working voltage |
---|---|
Lo15 | 24V |
T37 | 24V |
T68 | 24V |
Teletypes with FSG
Teletype | Working voltage | Full Working voltage |
---|---|---|
Can transmit, receive and dial but the ready-for-dial-lamp lits always. | Can transmit, receive and dial with ready-for-dial-lamp working as expected. | |
T37 | 50V | ? |
T68 | 55V | 85V |
T100S | 24V | 60V |
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Test and Maintenance Power Supply
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Power Supply for TW39 Interface WITHOUT using a FSG
External Supply
Transformer based
Power Supply for TW39 Interface WITH using a FSG
External Supply
Transformer based
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60 Volt DC/DC Hack
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