Friday, July 20, 2018

My model 15 teletype working great, plus prep for VCF West exhibition


I updated the configuration file for the BaudotRSS program that will drive the model 15 teletype at the festival. It will allow us to print news or weather reports, producing that wonderful newsroom sound and some output that can be handed to attendees.

The program was set up by default to assume that the teletype does a linefeed after every carriage return, but that is not true of our model 15s. I changed the code to interject a LF after each return. The other change was to specify weather reports for Mountain View where the festival takes place, and add some interesting news sources to print. 

I moved my ASR 33 into the garage, mounted it on its stand and loaded blank paper tape in preparation for punching out the demo programs. I couldn't figure out how to punch leader - an ASCII null character - since there was no visible key on the keyboard for it.

I decided that I could switch to Line mode with nothing wired up, which causes the machine to see a continual stream of null characters and thus punch them as leader. Now I am ready to punch my demo tapes, hooking my PC to the teletype with a USB to serial connector and MAX3232 voltage converter.

I bought a wooden cabinet that was a reasonable fit, although not perfect, for the SBC 6120 computer. Acrylic blocks glued to the rear of the computer front panel will hold it in place in the opening of the box and allow the power cord and RS232 cables to run out the bottom.

Bob Rosenbloom will be bringing in a non-working ASR 33 mechanism to set on the desktop to let people look inside and see how the machine is constructed.


This morning I identified some areas that might be causing the failure of the ribbon of my model 15 to advance properly. The first thing I spotted in the diagrams was a 'ribbon lockout lever' which is probably activated. Sigh.

After arriving at Marc's I spent time on two aspects of my teletype, the ribbon mechanism and the selector mechanism. Typing does not show up on the paper and the ribbon does not advance. The selector vanes move a bit sluggishly, vane five is not deflecting to its end positions and there are erratic mistyping results of the vanes not following the input data stream.

First up, I lubricated and exercised the selector mechanism and vanes until they felt free and didn't appear to stick at all. Then I was ready to hook up the teletype to my computer interface box and begin some testing. That is, after I attended to the nonfunctioning ribbon.

I looked closely at the printer. Yes, indeedy, my ribbon lock lever was set. I unlocked the mechanism and then turned on the teletype and interface. After a bit of adjustment of the 'range finder' which determines the spot during each bit cell that the condition is sensed, my machine began to type flawlessly.

Alas, the ribbon was not winding, but it is at least printing nicely when I manually shift the ribbon a bit. Once I attend to this last part of the task, this model 15 will be ready for its role printing at VCF West.

I tried out the weather forecast mode and indeed it printed the forecast for Mountain View, California, the site of the festival. Once I have the ribbon advance working properly I can try out the newsfeed mechanism.
Weather report printed on old paper
After quite a bit of lubrication and a good 30 minutes of turning of the most stucky of the ribbon reel gears, I got everything freed up and looking good. The machine was reassembled and went right into service, typing flawlessly with the new ribbon and new paper.

Model 15 as it will sit at VCF West
Something is not right about the newsfeed option - presumably this will print the top stories from selected RSS feeds - since the program complained that there were no new stories. Ken Shirriff helped investigate the malfunction and it appears that the way I have Python 2.7 and Python 3 installed on my laptop is causing some conflicts and impacting the program execution.

I plan to install just Python 2.7 on a desktop computer I own, giving a pure environment for the BaudotRSS program. If that seems to work without a teletype attached, I can do a final verification at Marc's house the next time I am there. 

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