

A 50 Year-old Teletype Powered by a Raspberry Pi - zdw
http://www.sudobob.com/teletype-pi/

======
Animats
It's good to see more people restoring these machines. I have a few of them
myself. They can all be interfaced to computers. They use standard serial port
data, 45 baud, 5 bits, no parity, 1.5 stop bits. (The signal level has to be
converted, though.) A Windows machine with a classic serial port outputs the
right waveform. Linux has some problems. Windows lets you set the baud rate as
a number. UNIX/Linux has a set of constants for speeds left over from the
PDP-11 era. A few USB to serial converters can be induced to run at that low
baud rate, too.

I usually run them off of RSS or SMS input. See
[http://www.aetherltd.com](http://www.aetherltd.com) and
[https://vimeo.com/97062822](https://vimeo.com/97062822) for info and video.

These machines aren't hard to get. They're on eBay all the time. In fact,
there's a Model 15 keyboard on eBay right now, which the machine shown lacks.
Unless they're seriously damaged, they can usually be brought back to full
operation. They were designed to be fully maintainable; they can be taken
apart down to individual parts and reassembled. No welds, no rivets, no glue;
it's all put together with machine screws. All the maintenance documentation
is available on line. There's a mailing list ("Greenkeys Digest") for people
who restore them.

I'm currently restoring my fifth machine, a Model 15 that was in a garage for
two decades after being lubricated with the wrong lubricant, dropped at least
once, and operated with a bent typebar guide which damaged some typebars. It
took a lot of cleaning and adjustment, but few new parts, to get it going.
It's now working OK, except that the "X" typebar is damaged and won't print,
and the print quality is bad. I'll be fixing that in a week or so.

[http://brassgoggles.co.uk/forum/index.php/topic,43672.0.html](http://brassgoggles.co.uk/forum/index.php/topic,43672.0.html)

The construction quality of these machines was very high by modern standards.

I'm a little bothered seeing someone run one of those machines in a public
setting with the covers off. There are pinch points, unguarded gears, exposed
live electrical connections, and the typebars have considerable power behind
them. I put steampunk cases, designed to show off the machine but keep fingers
out of the gears, on mine.

~~~
cnvogel
> UNIX/Linux has a set of constants for speeds left over from the PDP-11 era

You are refering to the B9600 (and other) constants set in the termios
tcsetattr() syscall. Those are indeed limited to a set of fixed rates between
110 and 115200 baud. But since a very, very, very long time Linux considered
B38400 a magic rate, and this baudrates' divisor could, if necessary, be
redefined by the setserial command to arbitrary speeds. (Default is 38400,
though).

[http://linux.die.net/man/8/setserial](http://linux.die.net/man/8/setserial)

[http://www.usconverters.com/downloads/support/aliasing-
baud-...](http://www.usconverters.com/downloads/support/aliasing-baud-rates-
usb-serial-adapter-linux.pdf)

I think there are more sane methods for some USB to serial adapters, though.

 _UPDATE_ : This seems to be the modern way to do it:
[http://stackoverflow.com/a/19992472](http://stackoverflow.com/a/19992472)
(specify BOTHER and fill out tio.c_ispeed, ospeed.

------
Aloha
I'm reasonably certain that Model 15 is older than 15 years, as they stopped
making them in 1963, and the bulk of the production was earlier.

Also as an aside - if you were using a model 33 or 37, you could use it with a
simple RS232 to current loop converter, and agetty on a linux boxen - then you
could use it as a log in device too, rather than just a serial/console printer
:-D

The other thing I don't get is why use the optoisolator relay setup, the
voltages involved are low enough that a normal 5v/250v relay would be
sufficient - perhaps the current draw is too high for the raspi to handle?

~~~
Animats
The Model 15 came out in 1930, and was produced through 1962 or so. Much of
the production was during WWII. It's hard to tell when a machine was made. The
motor, typing unit, keyboard, and base are all very easily removed and
interchanged. It was normal Bell System, Western Union, and U.S. Army practice
to swap those in the field and send them back to a depot for cleaning and
repair, so the components may be from different periods. Rubber pressure
rollers under the platen indicate a post-WWII machine - earlier machines used
wood, because oil-resistant synthetic rubber wasn't available in 1930.

Most relays aren't fast enough to handle the 45 baud data rate. The relays
that are tend to have small contacts, and thus arcing and contact burn
problems with the inductive kick from the selector magnets. The Omron
G3VM-401B is a good solid-state opto-isolated relay for the job; it can handle
400V, and costs about $2.50.

------
alexose
In the spirit of repurposing old hardware with a Raspberry Pi, here's a
project I did with an old rotary phone:

[http://alexose.blogspot.com/2012/07/the-rotary-voip-
phone.ht...](http://alexose.blogspot.com/2012/07/the-rotary-voip-phone.html)

~~~
unimpressive
The USB receiver circuit is super cool. Thanks.

