ASR33

From: Philip.Belben_at_powertech.co.uk <(Philip.Belben_at_powertech.co.uk)>
Date: Wed May 13 08:24:09 1998

Tony Duell wrote:

> I'm pretty sure the teletype is a passive device and expects the other
> device to source the loop current.
>
> 5V should be enough for the transmitter loop (which is just switch
> contacts), but I doubt if it would be enough for the receiver loop (more
> like 12V or more here)

I used a TTY ASR-33 as a printer for my PET years ago. My memory is
that if I left the receiver open circuit, i yammered away printing
nulls; if I shorted out the loop it didn't. I interfaced it using one
transistor - no power supply was necessary.

                         +----------------------
                         |
OUT b |/c
-------/\/\/\/---------| NPN TTY
                       |\e
PET |
-------------------------+----------------------
GND

Note: I never interfaced the TTY transmitter - not even for reading
paper tape (don't know why not)

Philip.
Received on Wed May 13 1998 - 08:24:09 BST