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Max The Magnificent
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Re: Current loop connections, etc.
Max The Magnificent   9/1/2013 4:25:20 PM
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@John Nagle: Model 33 machines, like all the Teletype machines back to 1924, use standard Underwood typewriter ribbons. You can still get all the necessary supplies. See my page at "http://aetherltd.com/supplies.html".

Thanks so much for sharing all this great advice

Max The Magnificent
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Re: ASR?
Max The Magnificent   9/1/2013 4:23:03 PM
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@David: I'd love to get this going for Max but I think the postage for an ASR to Australia would be prohibitive..... :-)

Have you ever thought of taking your lovely wife on a vacation to the USA? You could visit Huntsville for a few days on your travels LOL

Max The Magnificent
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Re: 20mA current loop
Max The Magnificent   9/1/2013 4:20:51 PM
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@antedeluvian: However it does appear the B&B do make a module that you want.

I must admit that I'd rather buy it than build it :-)

Max The Magnificent
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Re: ASR33 Memories
Max The Magnificent   9/1/2013 4:19:45 PM
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@DataBass: A wonderful blast from the past.

Wait till you hear the sound -- when I get it fully up and running I'll take a video of it with sound. And if you are ever passing through Huntsville, Alabama, you'lll have tio drop by my office to see it and say hello.

 

Max The Magnificent
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Re: ASR?
Max The Magnificent   9/1/2013 4:17:57 PM
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@Dunae: I could be wrong though. I really don't know the principles behind the current loop.

I'd like to say that was helpful... LOL

David Ashton
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Re: ASR?
David Ashton   9/1/2013 6:04:51 AM
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Hi Duane...

>It's a 1979 vintage Super Elf based in the CDP1802

Mmmm...tasty.  Never had much to do with the 1802s but I know a lot of people liked them.  Maybe you should get it talking to Max's ASR.....

Ref the old mechanical teleprinters....they had some really clever ways of doing things then, but they were usually incredibly reliable.  I once looked after a fleet of 6 T100 (mechanical) teleprinters for a year and a bit, and the most I had to do was replace a set of motor brushes.   Siemens' successor to that machine was the T1000, all electronic, and we had so many problems with them.  The ribbon  direction-change mechanism in particular was a horror, finicky to adjust and very unreliable.  Such is progress.

In the European-influenced world, teleprinters were almost invariably 5-bit Baudot, which is tricky to interface with computers.  At least your ASRs talk ASCII which is intelligible to PCs with serial ports.

Mike Fahrion
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Current Loop Converter
Mike Fahrion   8/31/2013 11:44:39 AM
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Max,

Great project - I'd be happy to set you up with a 232 to current loop converter to help you get that thing talking. Drop me a note at mfahrion@bb-elec.com. You'd be suprised how often current loop is still in use!

 

-Mike

 

Duane Benson
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Re: Current loop connections, etc.
Duane Benson   8/31/2013 11:12:49 AM
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John - Thanks for the information. Upon a little more reading, it certainly does seem like it wouldn't be worth trying to build a converter. Although, it might be worth trying just for fun. I'd certainly hate to do something wrong and damage a 40 year old piece of equipment though.

Duane Benson
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Re: ASR?
Duane Benson   8/31/2013 11:08:40 AM
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Great information David. I actually have an old, old single board computer with a 20mA current loop. It's a 1979 vintage Super Elf based in the CDP1802. I have no idea if the current loop portion of it works though.

These early electro-mechanical or mostly mechanical devices like the ASR-33 are really fascinating. Funny that I see them as incredibly complex and almost beyond my comprehension, where a nice little MCU powered device, like a Beagleboard, seems relatively easy to understand.

John Nagle
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Current loop connections, etc.
John Nagle   8/31/2013 2:47:43 AM
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For 20mA, buy a commercial converter. It's not worth the trouble of building one. I restore pre-WWII Teletype machines and build 60mA interfaces for those, but there, the current loop is really driving the selector magnet directly, and there's inductive kickback to deal with. The ASR-33 has a transistor driver inside; whether it's current loop or RS-232, it's just a signal, not electromagnet drive.

Model 33 machines, like all the Teletype machines back to 1924, use standard Underwood typewriter ribbons. You can still get all the necessary supplies. See my page at "http://aetherltd.com/supplies.html".  There were at one time extra-heavy-duty ribbons for Teletypes, and although you can find those as surplus, they're too dried out to use today. Paper rolls are easy to get; paper tape is available but quite expensive.

It's even possible to reverse the yellowing of the plastic, which is a consequence of a bromine compound used during moulding. Look up "RetroBrite"

These machines are well understood, the documentation is available, and there's a discussion list ("Greenkeys Digest") for Teletype machines. I don't bother with the later models like the ASR33, but there are people on that list who do. The older models (1924 through WWII) are very rugged; I've restored four of them starting from fair to poor condition.

 

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