13 May
1998
13 May
'98
8:06 a.m.
Philip.Belben(a)powertech.co.uk wrote:
Tony Duell wrote:
Well, I tried this out, and to my surprise it did indeed wor
(that is, shorting the wires.) Now I just have to look in my
box of odds and ends to find the parts to make this little
interface.
Thanks,
Edward
--
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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.