标签: Terminal

A few months ago, I presented an online course on "Basic Industrial Control Systems". As part of that course, we discussed the computer systems of yesteryear, and I mentioned the fact that I would really like to get my hands on an old teleprinter (also known as a teletypewriter, teletype, or TTY). These electromechanical typewriters were used to send and receive typed messages from point-to-point. They were also used as input/output devices for early mainframe computers. Furthermore, for the purposes of creating programs offline, you could get them equipped with paper tape and/or punched card readers and writers. Well, a few weeks ago I received an email from Leo Sieben, who hails from Memphis, Tenn. Leo had been watching my course, and he thought to himself: "I have an old ASR-33 teletype in storage; I wonder if Max would be interested in it?" So Leo emailed me, and I jumped up and down in excitement (it's possibly that a little high-pitched squealing was involved) and told him that I would be very interested in this little beauty. Thus it was that last weekend found me taking a road trip to Memphis to meet up with Leo in his lair. The photo below shows Leo standing with his beloved teletype:   As you can see, this little scamp (the ASR-33, not Leo) has a keyboard, printer, paper tape reader, and paper tape punch (there's also a copy holder, which isn't shown in this picture because we'd already taken it off prior to opening the beast). After eating lunch at Fino's, which Leo enthusiastically proclaims to be the best deli in Memphis, we removed the cover to peruse and ponder the internals as shown below:   While the cover was off, with no small amount of trepidation, we decided to power-up the beast, resulting in a conversation that went something like this: Leo: Have you plugged it in the wall yet? Max: I'm just about to; are you ready? Leo: Yes... No... Yes... Max: OK, it's plugged in. Leo: There's no smoke so far. Shall I turn it on? Max: Yes... No... Yes... Leo: OK, I'm turning it on... (deep breath) ...now! And he did. And the motor started chuntering away to itself. And everything was well with the world. The rubber drive belts look almost as good as new, which is pretty amazing when you come to think about it. And, even though this little scamp has been in dry storage for 30 years or so, even the print ribbon still works. We tried entering a few words on the keyboard. The type is faint on the paper, but it's there. Now I need to get a new ribbon. Also, the paper tape punch works. We turned it on and then keyed-in a few characters on the keyboard and watched the holes being punched in the tape. It was all very satisfying indeed. Two things that don't work at the moment are the Carriage-Return/ Linefeed key and the Bell key. However, to be honest, after 30 years, I'm amazed that everything works as well as it does. I've also been reacquainting myself with some of the little details that I'd forgotten over the years. For example, consider the four translucent plastic control buttons sitting over the paper tape punch as shown below:     You would be forgiven for thinking that these were each connected to individual electrical switches under the cover, but then you'd be forgetting the electromechanical nature of this thing. When we lift the cover, we are presented with the following sight:     Observe the metal "paddle" on the right-hand-side, with two flat plates: one at the top and one at the bottom. Two of the spring-loaded translucent plastic buttons are used to toggle this paddle from one state to another, thereby effecting both electrical and mechanical changes. Last, but certainly not least, we see my ASR-33 ("my precious") in its new home sitting outside the door to my office (this photo was taken before I added the rolls of paper and tape back in). Why outside my door? Because I want everyone walking past to feast their eyes on this little beauty and to drool over it and lust after it (cue maniacal cackling sound effect).     So, what's the next move? Well, first of all, since Huntsville, Ala., has been so involved in computers for decades (due to its large presence in the military and space and engineering fields), there must be someone around who used to service and maintain teletypes. All I have to do is track them down and see if they would be interested in coming and walking me through the maintenance procedures. Once I've had my ASR-33 serviced, I would like to connect it to the computer in my office. I'm thinking of having a little HyperTerminal window in the corner of one screen. When someone walks by, I can type a simple message like "Hello There!" and hit the return key, thereby causing this message to print out on the teletype—and punch out on the paper tape—with a cheery ring of the bell thrown in for good measure. The bell will attract the person's attention causing him to move closer and peer down, at which time I might follow up with a merry quip along the lines of: "What? You wore a red tie with that shirt???" Communication with this teletype is based on a 20mA current loop. So the first thing I will need will be a bidirectional current loop to RS-232 converter. Now, I could run an RS-232 cable to my tower computer (which still has a serial interface), but the SNAP wireless modules from Synapse Wireless also support RS-232. Based on this, I'm thinking that it should be relatively easy to use a wireless link to connect my compute to the teletype. Watch this space...