On Sun, 4 Aug 2019 19:46:15 +0100, "NY"  declaimed the
following:

>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?
>

 In that day and age -- no IR LEDs, and no microcontrollers to
encode/decode data. Two whistle tones (one per button) are easy to decode
with simple RC bandpass filters (or even just a high-pass and low-pass),
and detected output from filter just kicked a stepper to the next position.


--
 Wulfraed                 Dennis Lee Bieber         AF6VN
 wlfraed@ix.netcom.com    http://wlfraed.microdiversity.freeddns.org/

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