🚀 go-pugleaf

In article <8486@ihlpl.ATT.COM> knudsen@ihlpl.ATT.COM (Knudsen) writes:
>Neat idea.  I just happen to own a pair of what must be the
>oldest type of DAC in existence.

      Maybe.  In the London Transport Museum at Covent Garden, there is
a device used to control a station display indicating the destination
of the next train.  It consists of a manual control box with a rotary
dial and lever, on which an operator indicated the train destination
when the train passed a signal box some distance up-line from the
station, a 4-bit shaft encoder in the box, a 4-bit by 32 shift register
used to store the train identification data, 1 of 16 decoder used
to decode the output of the shift register, and a sign with illuminated
sections for each possible destination.  All very straightforward
digital logic.

      But it's all implemented with 1890s technology.  The shaft encoder
has huge brass cams.  The shift register is an electromechanical device
about four feet high, using a drum with pins depressed by solenoids as
the storage medium.  The drum is powered by a large weight on a rope,
as in a clock tower, driving a gear train and an escapement released
by a solenoid.  The 1 out of 16 decoder is a beautiful device of
green solenoids nearly six inches long driving big brass switches,
all mounted on a polished wooden panel; the four stages of decoding
are laid out clearly for all to see.  

      The elegance of this device lies in its clear enunciation of the
basic principles of binary representation.  One doesn't usually see
explicit binary representation in devices of that era.  The Duo-Art
is one of the few others of which I am aware; other attempts to
perform the same function in player pianos were usually analog devices.

					John Nagle