[GreenKeys] (no subject)

[Duncan Brown]

On 12/19/2025 5:27 PM, Harold Hallikainen via GreenKeys wrote:
> The tape reader is interesting. Instead of a distributor like the model 14
> TD, it appears there is a cam that pushes up the hole sense pins one at a
> time. I suspect there is a switch for each of the hole sense pins. If they
> are open when the pin is down and close if the pin can go up (mark), and
> the switches are in parallel, we get the parallel to serial conversion by
> just sensing the holes one at a time. Again, clever!
>
> Harold
> https://w6iwi.org

Harold,

My first immersion into TTYs was in the US Army as a TTY repairman. I 
wondered why the Kleinschmidt tape readers were so simple compared with 
the old Teletype Corp. M14 tape readers with the big distributor.

It turns out, that from Emile Baudot's day (1880s) into the 1920s, all 
keyboard and tape readers operated with parallel output. The 5-bit 
parallel signal of multiple units was then sent to a distributor to 
produce a time division multiplexed signal.

When the Start-Stop method was started in the mid 1920s, they continued 
to use the old parallel tape readers, but now each tape reader needed 
its own distributor to convert it to serial, thus the name 
"Transmitter-Distributor."

The next generation of TTYs (Kleinschmidt Labs and Teletype Corp. M28)  
in 1950 were all serial and simplified things with just one transmitter 
contact and they used cams to produce the proper timing.
I assume that the European  M14 & M15s with tape readers did the same thing.

So the Kleinschmidt and M28 tape readers read the tape sequentially and 
generate the serial data signal directly, no need for the 
parallel-to-serial conversion of a "distributor".

(I don't know why they went back to a distributor in the M33)

Have fun,

Duncan
K2OEQ