[GreenKeys] Parallel to Current Loop Conversion - 6402 UART circuits

[Doug via GreenKeys]

Cory.  Not sure if this is what you are looking for, but the old 6402 UART IC works fine.  The first link below shows it in a parallel to serial
converter mode.  I have used this exact circuit with optical tape punch reader equipment, and it works fine.  You may have to configure some of 
the control pins different for your setup.  In my setup, I used the signal from the sprocket hole as the trigger input, pin 23.  I was using it at 110 
and 300 baud.  I ran the serial output into a cheap $2 USB serial adapter from eBay, and it worked fine on my Windows XP computer using 
hyperterminal to send and receive data.  I don't think they still make the 6402 , but you can still find it pretty easily.  A modern UART might be 
cheaper, and will have more functions, but I wanted to keep it old school in my project.  If anyone is curious, the second link is for the 6402 in a 
serial to parallel mode. 

http://www.seekic.com/circuit_diagram/Communication_Circuit/SERIAL_TRANSMITTER_CIRCUIT.html

http://www.seekic.com/circuit_diagram/Basic_Circuit/RS232_TO_PARALLEL_DATA_CONVERTER.html

Doug Wirth

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On Thu, 12/4/14, Cory Heisterkamp <coryheisterkamp at gmail.com> wrote:

 Subject: [GreenKeys] Parallel to Current Loop Conversion
 To: "greenkeys" <greenkeys at mailman.qth.net>
 Date: Thursday, December 4, 2014, 3:15 PM
 
 Before I go
 and reinvent the wheel, I was wondering if anyone had a
 proven old school circuit (no micros) for converting
 parallel 8-bit data to ASR-33/35 friendly 110 baud
 equivalent. This won't be a computer interface, rather
 the parallel source will either be switches or relays with
 an additional line to 'release' the data when ready.
 
 
 Intersil use to make an IC that would generate various
 bit rates including 110, and I could sequence a pair of
 8-bit shift registers (8 data plus a fixed start and two
 stop bits) to drive a relay for the current loop. A 4-bit
 counter would reset the shifters. With a couple dip switches
 I could reconfigure this for 5-level Baudot at a different
 bit rate to play nice with the model 28's.
 
 Or maybe I should hack an old test set. Thoughts? 
 -Cory