20ma current loop to RS-232 conversion

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Revision as of 09:08, 21 August 2015 by Jeffa (talk | contribs) (→My ASR hookup: Add schematic connection column to wire legend)
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20ma current loop <> RS-232 conversion

Vintage PCB

Dig this crazy circuit board man! Still in it's original packaging from Hobby World Electronics in Northridge California.

Additional Resources

  • Helpful article, Teletype 101 from vintagecomputer.net
  • Another circuit. From [Altairclone] Specifically designed to fit in a Teletype model 33 using only a 12vdc wall wart for power.
  • Another circuit I found referenced on the greenkeys email list

My ASR hookup

I built the circuit described above from the altairclone site. I found the Teletype 101 article helpful for identifying the proper terminal strip locations. The interface works. I set baud to 110, with 7 bits and 'mark' parity in TeraTerm on a windows 8 notebook with a Gigaware USB<> serial convereter. 

                             screw       my wire          schematic
Signal                      terminal      color           connection
---------------------------------------------------------------------
Transmitted data send (+)      7          orange          Data to Teletype +
Transmitted data return (-)    6          brown           Data to Teletype -

Received data send (+)         4          red             Data from Teletype +
Received data return (-)       3          black           Data from Teletype -

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