Selectric Typewriter conversions

From: Merle K. Peirce <>
Date: Wed Feb 5 10:07:31 2003

There was a lot of major work on the Underground, ca 1923-1926. It might
well date from that period.

On Wed, 5 Feb 2003, Tony Duell wrote:

> > I've seen a 3-bit-binary to one-of-eight decoder built out of
> > huge brass and bakelite relays. It's in the London Transport Museum,
> > and was used to drive the train indicators on the platforms of
> There wasa similar thing used to decode the 4-bit code as to what train
> was expected next, used in signal boxes, etc on the London Underground.
> That was certainly (large) mechanical relays.
> The 4-bit train descriptor codes were stored in an electromechanical FIFO,
> consisting of a drum with a number of rows of 4 pegs around it. Each peg
> could be in one of 2 states (towards the spindle or shifted away from the
> spindle. There was a fixed solenoid mechanism to set the pegs, the whole
> drum then moved round one position (equivalent to incremementing the
> write pointer in a software FIFO). There was a separately revolving
> contact assembly to sense the position of each row of pegs and feed it to
> the decoder. This was stepped on as each train came through -- equivalent
> to incrememnting the read pointer.
> The whole thing is _exactly_ like the classic software FIFO we've all
> implelmented many times. I don't know when it was built, but around 1920?
> It's described in detail in an old book I have called 'Modern Electrical
> Engineering' which alas has no dates on it.
> -tony

M. K. Peirce

Rhode Island Computer Museum, Inc.
Shady Lea, Rhode Island

"Casta est quam nemo rogavit."
              - Ovid
Received on Wed Feb 05 2003 - 10:07:31 GMT

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