Take that scope probe out of your mouth -- you're mumbling -- I'm not expert enough to know -- Leo said it was an ASR-33 -- also, if you go to this page on Wikipedia, the photo they say is an ASR-33 looks like my unit -- maybe some other reader can cast light on this topic...
Half your luck Max, it is a thing of beauty indeed. From my limited understanding of these devices, KSR-33's were keyboard only (Keyboard Send-Receive) and ASR-33's had the tape punch and reader (Automatic Send-receive).
I had a lot to do with the Siemens T-100, the European equivalent, but they used Baudot code (5 Bits) not ASCII (7 or 8 bits) like yours. I also trained on an even earlier British model, the Creed 7B, and had a lot of fun with them, see
Love the idea of having it greet visitors to your office Max, I howp you get that going. I have seen an RS-232 to 20-mA loop converter circuit somewhere, but I have no idea where. Do you know if it is half-duplex (both send and receive on the same loop) or full (2 separate loops)?
At a quick glance looks like the default is FDX which makes life much easier for a converter. I daresay someone on the site would know lots more. The site aht led me her had some comments by people who'd tried to get one going and had problems as the grease had solidified, so if yours apears to work you're doing well....
@Max....Fossick - usually used in connection with prospecting, but more widely meaning "to have a root around looking for something". But you wouldn't use that in Australia - "root" means something not mentionable in a family column like this......
However said fossick may not be necessary. I think this will do what you want:
I've never bought anything off B&B but get their newsletter and their website (for a comms person) if quite tasty. I've never heard a bad word about them and I think they might even assist you to set it up with your ASR. Have a look.
David, Max - That's a lot of circuitry for a 20mA to RS232 converter. I have to believe that it could be done with an MCU, a MAX232 and a few discrete components. I could be wrong though. I really don't know the principles behind the current loop.
@Duane ... Current loop...now there's a can of worms.
In RS232, -ve voltage (-3 to -15V to be exact) means 1, and +ve means 0.
In the old teleprinter current loop world, 20mA meant 1 and no current meant 0.
(That is if you're using single current. If you're using double current, it's +20mA and -20mA, but that's not much used so let's keep things simple).)
So Max's ASR33 has two sets of terminals, receive which wants a 20mA / 0 current supplied to it, and transmit which usually provides 20mA or 0. These would often be provided at up to 60 or 80V, for transmission down long lines (Sounds awful but don't forget they only work at 50,60,100 or 110 baud depending on the standard where you are). You'd usually common one of each sets of terminals to earth (ground) so you only need 2 wires (at least that's how we did it). When you're not using long lines then 12V is usually sufficient to provide 20mA. We used to have a nice multi-turn wire-wound pot in each line to adjust the current to exactly 20mA and I still have a couple of +/-20mA meters lying around.....
In old machines like I used to work with, and I think Max's ASR, the receive device is a magnet which, on the first 0 which is a start bit, trips a mechanical process which then selects a character to print based on the next 7 bits. A similar mechanical process sends the start, data and stop bits of the character corresponding to a key press. These mechanical devices were things of wonder to me, being an electronics guy with the benefit of shift registers and stuff like that, but teleprinters were around long before TTL was a gleam in someone's eye....
You could use half-duplex, where the receive magnet and transmit contact were in series. As long as you only did one thing at a time you wer fine. Then you could have local battery (you provide the current) or remote battery (the other end provides the current). And you only needed one wire and ground.
Yes, B&B's converter has a lot inside it and you can do it a lot more simply, especially if you don't want isolation (B&B's has opto-isolators on both circuits). it also has U4 to provide a - voltage for the RS-232 side. But for 69 bucks I don't think I could do anything better in less than a good few hours work..... You note that the transmit circuit just switches current, you'd need to wire it in with the RES12V and RES1/2 terminals to actually provide a current for the ASR. You'd have to look at the ASR circuitry to work out exactly how to do it
I'd love to get this going for Max but I think the postage for an ASR to Australia would be prohibitive..... :-)
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.
>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.
When I had an ASR-33 in the basement I had a program called "Fancy Punch" that was written in basic and ran on my Southwest Technical Products 6800 computer system. "Fancy Punch" would allow you to send a line of text to the ASR and have it come out as legible punched characters on the paper tape. My copy of the program is long gone, but it shouldn't be that hard to re-create it.
@Rick I used to do that manually with my old Baudot machines. You just needed to know what characters to use to get the right holes in the tape. for instance "Z" gave the two outside holes and "C" gave the 3 inside holes (only 5 bits remember!) so to get an "O" on the tape you'd key CZZZC. The problem as I remember was getting a space with no holes punched in the tape. Of course Max's machine is ASCII so that would probably make it easier. And with 7 holes in the tape you could do 7x5 characters instead of my 5x5 ones. I could do a program for this in BASIC quite easily, just a lookup table really.
@David: Is it half red and half black (red = tx, black = rx)?
The current tape is just black, but that's not to say that the machine couldn't handle a red/black tape -- when I get it working I'll stick a red/black tape in there and see what happens -- thanks for thinking of this...
When I used one of these things, the tape was all black. I was a law enforcement explorer scout at the time and the police department would let us kids run dispatch. We were really cheap labor.
If I recall correctly, it could receive automatically when idling: The state computer would sometimes broadcast messages to be printed on the paper. The number of bells would indicate the level of importance.
When I had a license to run, I'd type it on to the paper tape. When done, I'd then cut off the paper tap and feed it into the tape reader, which would send it off to the state computer. Several minutes later, the reply would print out on the roll paper.
Pretty hi-tech for the mid-70's in the logger town I grew up in.
I'm somewhat envious and can envision all sorts of fun uses for one of those things.
Model 33 ASR, (Automatic Send and Receive), built in 8-level tape reader and punch.
Model 33 KSR (Keyboard Send and Receive), no paper tape reader or punch.
Model 33 RO (Receive Only) printer only, no keyboard, reader or punch.
One thing to look out for is the rubber print hammer in front of the cylindrical print wheel, they go off with age and can destroy the print cylinder which are now very hard to obtain. The were available in many variants accorcing to the typeface used on the machine and the country.
Before using the ASR check the print hammer, the usual replacement is a short length of clear thick plastic hose pushed over the plate the original rubber one fitted to. There is a guy in California with most of the stock of Teletype spares.
@terrapindundee: One thing to look out for is the rubber print hammer in front of the cylindrical print wheel, they go off with age and can destroy the print cylinder which are now very hard to obtain.
Thanks for reminding me -- in fact Leo (the original owner) did menton this and we looked at the rubber print hammer .... like all of the other rubber element sof thsi device (belts etc) the print happer is actually in incredibly good condition.
All I really need to do is sort out the linefeed and bell problems -- and I bet those can be solved with a basic cleaning (de-gunking).
Hi, I have fond memories and some not so fond memories of that ASR33. One might benefit from my experience. I used it mainly as an I/O terminal to a Data General Mini Computer, Nova 3 and 4's...where it worked fine loading bootstraps and user input/output. When microprocessors came out in the middle 70's, I needed the ultimate in reliability for reading 8 KB paper tapes for Basic and other Software. The BER, Bit Error rate was less than desired, so I found the ASR-33 delighfully easy to take apart, clean, re assemble etc generall R&R, but often the BER rate when up surprisingly. The correct weight lubricant was most important to get ultra reliable operation.. and the correct weight lubricant was much lighter than I would have ever expected. I don't remember specifically what I used, but I believe it was specified in the manual. Likely the machine will have to be cleaned and likely relubricated.. so pay attention to using the lightest lubricant you can find or specified .. MrPixel@gmail.com used the machine at was was then called Highway Safety Research Institute, Ann Arbor Michigan. Best Wishes Leigh
I suspect Karen has been off with the fairies the past year or two. But it is nice to see her commenting so much again now. Let's hope her new Design West responsibilities don't take her away from that too much.
@kfield: ... and wonder why you didn't call out the propeller beanie? I should have, but for every item I did call out there are 50 more hiding in the shadows.
When I went to the Huntsville Hamfest last week, APP member Rick Curl had brought his propeller beanie -- if I'd known he was bringing it I woudl have taken mine -- as it was he looked a bit silly being the only one wearing one LOL
A wonderful blast from the past. In my junior year of highscheel (1970-71) I discovered computers and found that I loved them. We started out with marked-sense cards (BASIC) then moved to punched cards (FORTRAN) that had to be sent elsewehere for procsesing. Next, the school district got an HP9800(?) and each school had a dedicated leaased line to a room with an ASR33. Boy I spent a lot of time in there, even when the school was officially closed for the day. Fortunately, I didn't cause any problems and neither did the janitor. Fun memories.
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.
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.
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.
@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".
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 firstname.lastname@example.org. You'd be suprised how often current loop is still in use!
I can think of a number of things to say about this subject, I actually did discard a Kleinschmidt recently (I don't recall the model but by the designation system iyou're using it was KSR, ie no paper tape) but I couldn't afford the space anymore and it was not in good enough shape to be worth the trouble and besides all the computer museums said they wouldn't be interested even if it were new fresh in the box. I guess my first question though is if you really want to be authentic, where's your acoustic coupler? (They usually sat on top of the right panel although I think I recall seeing some that were actually BUILT INTO it, but that may have been an aftermarket upgrade.) Might make another project to see if you can find one somewhere and get that working...
It's also just possible there's still a few folks around who remember the old Model 19s (and how they could remain in active service for DECADES, frequently as the old AP or UPI "wire service" especially at broadcast stations and newspapers). When people who had been maintaining the old machines first saw the 33s you heard a lot of lightly concealed swearing about "bucket of plastic rattles" (especially if they learned THEY would have to maintain them!) which is true enough if you compare these next to the older machines which hardly had ANY plastic at all. If one of THOSE guys saw you raving over your latest acquisition they'd probably choke on their coffee, but I guess there aren't too many of them around to do that!
@JeffL_2: ...but I couldn't afford the space anymore and it was not in good enough shape to be worth the trouble and besides all the computer museums said they wouldn't be interested even if it were new fresh in the box.
I simply cannot believe that anyone wouldn;t want one fresh out of the box -- especially museums ... it's a sad world...
If I remember correctly, line feed was triggered by a small metal piece under the carriage. When the carriage returned to the left side, it pressed a paddle that advanced the platen. It was held on with one screw, and if it ever got turned out of position, it stopped pressing the paddle. The printer can be removed and flipped over to fix it, but remember that the punch and reader are both driven from the print mechanism and are connected.
@n1ist: The printer can be removed and flipped over to fix it, but remember that the punch and reader are both driven from the print mechanism and are connected.
I now have links to all the maintanance manuals online ... so it may come to that -- but I still live in hopes of finding someone local who used to maintain these, because they coudl do it so much faster and more efficiently...
I first used these in high school, connected over leased current loop lines (Ma Bell) to a shared computer in an adjacent school district. When I was in college (30+ years ago), these were all over, some hardwired, some on Anderson Jacobsen 110 baud modems in wooden boxes. The ASR33s were under service contract. When one would break, the service provider would bring a complete replacement machine, at no charge, provided they did NOT have to take the old one back. It seems that as these machines became obsolete, they had a warehouse filled with ones fresh off lease. Our broken machines were carted away to a room in the basement of the Buchard Building, housing EE and Physics. Soon we didn't bother calling service, as it was faster to scavenge parts from the growing pile in the basement. Every once in a while, rumaging through my junk at home, I come upon a motor start relay from an ASR33.
Fond Memories indeed. I worked at a place that used ASR33s as the interface to Data General DG3s (mini computers from yesterday).
Before that, I had a Creed set up to run RTTY (Radio Teletype) on both HF and VHF. For a while, I was broadcast officer for a amateur radio club (HAMs) and was responsible for doing a weekly RTTY broadcast. The problem is when you mis-type a character, you can start from scratch (again!) or just live with it. Broadcast ran for around 5-10 minutes at 50 baud. You can imagine the amount of paper tape consumed in the process. Computers fixed all that.
Setting these up is not for the feint hearted. Max, get someone to do it for you. I knew a bloke who could listen to a TTY and tell you what was being transmitted - kind of like a complicated Morse code.