building my own relay computer

Peter Corlett abuse at
Sat Feb 14 09:37:58 CST 2015

On Fri, Feb 13, 2015 at 06:14:53PM -0700, ben wrote:
> The alu has never relay been a problem with relays, but what about main
> storage? Punched tape (paper/film/card) is no longer with us for I/O.

How about audio tones, as was popular in the eighties?

That is the *eighteen*-eighties! The "harmonic telegraph" was a new development
in that decade. The principle was that it multiplexed different Morse streams
onto a single audio channel by using a different tone for each, and the
demultiplexing at the far end was done using a tuning forks which resonated at
the appropriate frequencies to close a circuit. (At this point it was
immediately realised that the sound source could be a human voice rather than
Morse keys, rendering the telegraph instantly obsolete.)

However, relay computers are more a 1940s technology, so one has the benefit of
valves in which one could implement a notch fiter and/or PLL to demodulate the
audio. Which period would you like to be appropriate to? :)

The other side of this is actually recording and replaying the audio. For
1880s, you're looking at wax cylinders, gramophones and whatnot, but we'd
pretty much figured out recording audio on magnetic tape by the 1940s. Compact
cassettes are from 1963, but I figure that if Zusie can use blue LEDs (1993,
and still expensive into the 2000s!) an old 1980s tape deck is fair game.

More information about the cctalk mailing list