6 Oct
2003
6 Oct
'03
1:51 p.m.
From: Ian Primus <ian_primus(a)yahoo.com>
One problem is that I don't know
what the Teletype is _supposed_ to do. I have never seen one
operational
Did you see my teletype page? It has movies of an operating teletype
http://www.pdp8.net/asr33/asr33.shtml Not too different than operation
in local mode.
I have been attempting to get my ASR33 teletype
connected to something
and communicating, but so far I have not been successful. I have built
the interface here :
http://www.daedalus.co.nz/~don/computing/20mahack.html
It looks pretty marginal, a lot of serial ports aren't going to have the
drive. I made a converter with optoisolators & rs-232 chips etc
which is a lot more complex than needed and also was a little strange since I
made it before I got that degree. If nobody has pointed you to a better one
I can scan my schematic, >15 years ago radio shack had the parts.
David Gesswein
http://www.pdp8.net/ -- Run an old computer with blinkenlights
Have any PDP-8 stuff you're willing to part with?
9 Oct
9 Oct
2:07 a.m.
Hello,
as for the "Line or Local" issue, you stated that the local side worked
fine. As in when
you type on the keys it prints what you type.
A rather simple test is to take a "fresh" 9 volt battery, find the two "RX
lines and connect
them to the battery, with the TTY in line mode the basket should quiet, if
it does, then
connect the keyboard leads between one side of the battery and the "RX" line
and try
typing again. If that works then your interface is lacking in the ability to
provide the
20/60 MA required by the TTY.
Jim
WB2FCN
----- Original Message -----
From: "David Gesswein" <djg(a)pdp8online.com>
To: <cctech(a)classiccmp.org>
Sent: Monday, October 06, 2003 9:51 PM
Subject: Re: ASR33 Teletype interfacing
From: Ian Primus <ian_primus(a)yahoo.com>
since I
One problem is that I don't know
what the Teletype is _supposed_ to do. I have never seen one
operational
Did you see my teletype page? It has movies of an operating teletype
http://www.pdp8.net/asr33/asr33.shtml Not too different than operation
in local mode.
I have been attempting to get my ASR33 teletype
connected to something
and communicating, but so far I have not been successful. I have built
the interface here :
http://www.daedalus.co.nz/~don/computing/20mahack.html
It looks pretty marginal, a lot of serial ports aren't going to have the
drive. I made a converter with optoisolators & rs-232 chips etc
which is a lot more complex than needed and also was a little strange made it before I got that degree. If nobody has
pointed you to a better
one
I can scan my schematic, >15 years ago radio shack
had the parts.
David Gesswein
http://www.pdp8.net/ -- Run an old computer with blinkenlights
Have any PDP-8 stuff you're willing to part with?
11 Oct
11 Oct
12:56 a.m.
On Thursday, October 9, 2003, at 10:07 AM, James M. Walker wrote:
Hello,
as for the "Line or Local" issue, you stated that the local side worked
fine. As in when
you type on the keys it prints what you type.
A rather simple test is to take a "fresh" 9 volt battery, find the two
"RX
lines and connect
them to the battery, with the TTY in line mode the basket should
quiet, if
it does, then
connect the keyboard leads between one side of the battery and the
"RX" line
and try
typing again. If that works then your interface is lacking in the
ability to
provide the
20/60 MA required by the TTY.
Jim
WB2FCN
I found a 9 volt battery in my workshop, and tested it on a multimeter,
and it came out to be 9.02 volts. Perfect! Then, I connected some
scraps of telephone wire to the barrier strip on the teletype, and
hooked the RX lines to the battery. It didn't help, so I switched the
wires on the battery, and that worked. The teletype stopped "running
open". Typing produced no effect. Then I unhooked one of the leads from
the battery, twisted it together with one of the TX lines, and
connected the other TX line to the radio battery. Once again, the
teletype was quiet, and this time, typing produced output on the page.
It looks like everything is working then, I just need to build an
interface that supplies the proper loop current. While I had the
battery connected, I typed three lines in Line mode to test it, then I
switched over to local mode and typed a couple lines, to make sure that
it did, in fact, still work in local mode. It did. But, when I turned
off the teletype, and went to unhook the battery, it was hot! I
unhooked the leads and tested it again on the multimeter - 8.07 volts.
I had no idea that the teletype used that much power just for the
current loop interface. 20mA isn't very much, but I guess for a little
radio battery it is. At least I know now that the teletype works
properly, now all I need is a better interface. Thanks for the help!
Ian Primus
ian_primus(a)yahoo.com
5:52 a.m.
Hi Ian and list,
Sorry there Ian, I should have mentioned that this technique is only
for testing purposes and also that the battery gets "HOT". This is an
old
trick I used while doing field setups and testing of Shio-To-Shore sites
that used ARQ and FEC with ASR-32/33 teletypes. The 20 MA loop can be
connected to your interface as described previously. All that is needed
is a 115v primary to 115 v secondary transformer, a full wave bridge to
rectify the AC and around 35 - 60 uF cap for filtering. All this output
is fed to the collector of an MJE-340 NPN transistor emitter, the
collector
connection goes to your ASR-(*) TTY. The base goes to the output from
the
tx terminals on the interface. I think I have an Orcad drawing of the
circuit if you would like it. As I recall it is an RS-232 to 20 MA
interface
and also includes an opto-isolator in the circuit. However at least you
did
get to verify that your TTY is indeed working correctly! Good "Oh!
Jim
Real Radio in Buffalo
Ian Primus wrote:
On Thursday, October 9, 2003, at 10:07 AM, James M. Walker wrote:
Hello,
as for the "Line or Local" issue, you stated that the local side worked
fine. As in when
you type on the keys it prints what you type.
A rather simple test is to take a "fresh" 9 volt battery, find the two
"RX
lines and connect
them to the battery, with the TTY in line mode the basket should
quiet, if
it does, then
connect the keyboard leads between one side of the battery and the
"RX" line
and try
typing again. If that works then your interface is lacking in the
ability to
provide the
20/60 MA required by the TTY.
Jim
WB2FCN
I found a 9 volt battery in my workshop, and tested it on a multimeter,
and it came out to be 9.02 volts. Perfect! Then, I connected some
scraps of telephone wire to the barrier strip on the teletype, and
hooked the RX lines to the battery. It didn't help, so I switched the
wires on the battery, and that worked. The teletype stopped "running
open". Typing produced no effect. Then I unhooked one of the leads from
the battery, twisted it together with one of the TX lines, and
connected the other TX line to the radio battery. Once again, the
teletype was quiet, and this time, typing produced output on the page.
It looks like everything is working then, I just need to build an
interface that supplies the proper loop current. While I had the
battery connected, I typed three lines in Line mode to test it, then I
switched over to local mode and typed a couple lines, to make sure that
it did, in fact, still work in local mode. It did. But, when I turned
off the teletype, and went to unhook the battery, it was hot! I
unhooked the leads and tested it again on the multimeter - 8.07 volts.
I had no idea that the teletype used that much power just for the
current loop interface. 20mA isn't very much, but I guess for a little
radio battery it is. At least I know now that the teletype works
properly, now all I need is a better interface. Thanks for the help!
Ian Primus
ian_primus(a)yahoo.com
12 Oct
12 Oct
2:01 p.m.
On Saturday, October 11, 2003, at 01:52 PM, James M. Walker wrote:
Hi Ian and list,
Sorry there Ian, I should have mentioned that this technique is only
for testing purposes and also that the battery gets "HOT". This is an
old
trick I used while doing field setups and testing of Shio-To-Shore
sites
that used ARQ and FEC with ASR-32/33 teletypes. The 20 MA loop can be
connected to your interface as described previously. All that is needed
is a 115v primary to 115 v secondary transformer, a full wave bridge to
rectify the AC and around 35 - 60 uF cap for filtering. All this
output
is fed to the collector of an MJE-340 NPN transistor emitter, the
collector
connection goes to your ASR-(*) TTY. The base goes to the output from
the
tx terminals on the interface. I think I have an Orcad drawing of the
circuit if you would like it. As I recall it is an RS-232 to 20 MA
interface
and also includes an opto-isolator in the circuit. However at least you
did
get to verify that your TTY is indeed working correctly! Good "Oh!
Jim
Real Radio in Buffalo
I would definitely be interested in seeing your circuit. I am quite
confused as to the proper way to go about doing this, from what I have
seen, it looks like there are several quite different ways of doing
what I want to do, and none of which I have been able to figure out
thus far. That little thing I built with the resistor and the diode I
somewhat understand, but then again, I also understand that it is _not_
a very good solution, and it looks like it might be dangerous to the
computer if I wasn't careful. Electronics aren't my strong suit,
although I am currently working on learning more. A friend and I are
building a little computer based around the Z80 CPU, and I am actually
beginning to understand memory decoding and addressing. But, analog
electronics is something that I have done very little with, save for
simple power supply repair and simple audio amplifiers. At the moment,
20mA current loops are over my head. Anything to help me understand
what is going on here would be greatly appreciated.
Also, yesterday I went to test the teletype again (I was cleaning the
type cylinder), and I happened to turn it into Line mode, and it didn't
run open like it had before. Then, I realized that the scraps of wire
were still connected to the terminals, with one of the RX lines tied to
one of the TX lines, and the other two wires were dangling, not
connected to anything. Disconnecting the RX and TX lines caused it to
run open again. Does this mean that the Teletype is supplying enough
loop current to drive the selector magnet, or what?
There seems to be forty different possible configurations for the
teletype, and a the Teletype itself involves circuits and mechanisms
that I don't understand. (IMHO, the ability to get that little cylinder
to rotate and bang out the proper letter is amazing in itself, even
more amazing is the fact that it's all done with levers and cams...)
Once again, any help to clarify things would be greatly appreciated,
one of these days I hope to be able to more fully comprehend these
things...
Thanks!
Ian Primus
ian_primus(a)yahoo.com
11 Oct
11 Oct
7:46 a.m.
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ard＠p850ug1.demon.co.uk -
chejmw＠acsu.buffalo.edu -
djg＠pdp8online.com -
ian_primus＠yahoo.com