"Dennis Lee Bieber"  wrote in message
news:8psdkelv38f1r7g9v7psorvt1fi728lm2v@4ax.com...
> And the remote functioned by sending an ultrasonic whistle chirp (each
> button compressed a bellows against a spring loaded valve -- when the
> pressure was high enough, the valve would open and the air would pass
> through a tuned frequency whistle port; different frequency for power vs
> volume).


I never knew that early ultrasonic remotes were mechanical whistles operated
by the buttons. I thought even ultrasonic remotes were electronic
(battery-powered oscillator feeding piezo transducer). Presumably later ones
were, to allow greater variety of frequencies for more operations (DTMF for
channel buttons, as for tone dialling on a phone except higher frequencies;
channel up/down; volume up/down; off/on) or else coding of binary pulses to
send various functions over two frequencies for 0 and 1.

I presume the same coding could be used for either ultrasonic or infra-red,
just using that code to modulate either two different US frequencies or two
different IR frequencies.

Was the choice of ultrasonic rather than infra-red driven by the need to be
mechanical rather than electronic at the remote, or was there some reason
why ultrasonic was preferable to IR irrespective of whether it was generated
mechanically or electronically?


I remember the VHS machines we used at school (in the sixth form, my prefect
"posting" was in the audio-visual room, so I was in my element!) were
top-loading, with arbitrary non-linear counters (ie not counting in minutes
and seconds) and with *wired* remotes, so neither ultrasonic nor infra-red.
They had the ability to play at 2x speed with reasonably intelligible sound
(there was some form of pitch shifting to prevent the Pinky and Perky
effect) or to play at various slower-than-normal speeds without sound.

--- SoupGate-Win32 v1.05