On 2016-02-07, Jim Wilkins wrote:
"Robert Nichols" wrote
in message ...
On 02/06/2016 02:38 PM, Jim Wilkins wrote:
"Ignoramus14059" wrote in
message ...
On 2016-02-06, Jim Wilkins wrote:


I often look at all that stuff, and I find extreme ingenuity with
which people overcame limitations of their current technologies,
it
is
fascinating.

i

Tbe one that impresses me most is the old analog telephone which
does
everything over two wires without active electronics, only one very
clever transformer, speaker and carbon mike. I couldn't quickly
find a
circuit description and should return to fixing my fallen TV
antenna
that had me abseiling down the snow-covered roof.

AT&T's original Touch Tone telephones had a clever circuit that
allowed a single transistor to oscillate on two frequencies at
once, with both frequencies closely controlled in both frequency
and relative amplitude. Yes, transistors were relatively
expensive back then.

--
Bob Nichols AT comcast.net I am "RNichols42"

Some Army phones had a 4x4 button pattern:
https://en.wikipedia.org/wiki/Autovon

We were warned not to touch the FO button unless we saw Soviet tanks.

Ah yes -- the "Flash Override" button. You really needed high
rank to use that one. :-) Those, of course, only worked on the "Autovon"
networks -- the typical exchange ignores them -- or drops a trouble card
on receiving them, but likely the person at the dial will never know
about that. :-)

And -- I have seen (and I think that I have, somewhere around
here), a keypad which uses the extra four keys, but labeled differently.

And -- the "card dialer" phones (plastic punched cards, punched
by hand) could generate those tones, too, if you knew what combinations
to punch.

Enjoy,
DoN.

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