On May 10, 2018 9:15:59 AM EDT, James Knott via talk <talk@gtalug.org> wrote:
On 05/10/2018 07:14 AM, Russell wrote:
I'm curious now, an answer back drum? Like a single spinning drum whos only task was to provide an ID/handshake signal?
It was a drum encoded with the ID information, typically a company name etc.. They held, IIRC, 21 characters. On the Model 32 & 33 Teletypes, they were solid plastic, with tabs that could be broken off to program the characters. Model 28 & 35 Teletypes used a metal drum where the tabs could be repositioned. Later devices
I use to similarly reprogram heavy duty washing machines and dryers for different duty cycles. Pop up tabs for hot and cold water and cycle lengths etc. The tabs would rotate on a drum and trigger the cycles. They were the same as commercial analog timers used to turn neon signs on and off at dusk and dawn, except there were several drums in each cluster. Like a music box, except that a sour note meant you'd immediately drain 50lbs of freshly heated clean water.
such as the Texas Instruments Silent 700 used a diode matrix, where individual diodes could be cut. When a certain code was received, typically Figs J, though sometimes Figs S (Telex was Figs J) on Baudot or WRU on ASCII, the answer back would be triggered.
I only ever fooled around with a telex in the radio shack at VE3OSC and all they'd let me touch was the keyboard.
I also used that station.
Well they let me practice morris on the old tap button once and a while on friday nights depending on the volunteer in charge. As a kid, the fancier left right button was a bit too sensitive for me to make any sense out of. I guess the real ham operators had tweaked that unit themselves and tightened up the swing arc. That one took a lot of coordination to get a message out quickly.
LTRS = long term return signal/state? like HELO OLEH?
No, letters shift. Since Baudot machines used a 5 bit code, there weren't enough combinations for all characters. So, there was a figures shift (Figs) for printing numbers & punctuation and letters shift (Ltrs) for text. A letters shift was all 5 bits mark, figures bits 1, 2, 4 & 5 mark, with bit 3 space.
https://en.wikipedia.org/wiki/Baudot_code
In industry, timing's are everything. Leveraging a mechanical advantage is as old as the oldest timepiece itself. It would make sense to me that the engineering of the day might take advantage of the mass in motion of a plattens own return movement, in order to advance the roll a notch or three on a sudden stop. I use to see those types of timing geegaws in manufacturing and industry all the time.
These days, with electronic controllers, it's a simple matter to buffer and wait as necessary. However, those Teletypes had a lot of mechanical activity that had to be properly synced. For example, in addition to moving the carriage back in time, the print hammer had to strike at the right time.
Back when I was a bench tech, I could overhaul, that is strip, clean, rebuild and test 2 M32 or M33 machines per day or 1 M28 or M35.
Metal dust from grinding gears can play havoc with electronics, not to mention other physical tolerances. Plastic, not so much but still can cause tricky problems. Interestingly the dust from streetcar braking tends to cluster around the electronics in neon and I guess other high voltage signs in the city, at least the ones that aren't cleaned by the elements. LED signs are everywhere now but neon is pretty much limited to rec room bar signs now. Hard to believe that back in the day, show time on the strip, was watching the Motel signs light up one by one at dusk and watching that first neon Mallard of the night land, fold up its wings and Duck Right Inn.
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-- Russell