Audio Animatronics Research 10-Nov-2010 8:38 PM
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Research

One step of this is to recreate a single-tone switch using a method similar to what Disney used originally.

To start with, the only information I could find is "a tone is used to vibrate a reed", without any more depth than that. I cannot find any more information past this. So I decided to figure out how to recreate this effect on my own.

First, my research brought me to modern day magnetic-sensitive reed switches like this one. My thought was that you could put one of these inline with a speaker assembly, and it would probably vibrate at some pitch. This might work, but would probably be less than optimal.

Next, I found this page which discusses a "PL decode reed" which I believe is the mechanism that I need. "PL" is short for "Motorola Private Line", although ICOM used it as well. (PL is also known as Continuous Tone Coded Squelch System (CTCSS)) It is essentially a tuning fork with one arm being magnitized. Both sides of the fork are in their own coils. When the first side is energized with the correct frequency, it resonates and vibrates the other side, which creates a field, and energizes it. This seems like a much less crude way to go.

In fact, the Motorola Vibrasponder seems to be the exact part needed to reproduce this mechanism, and very well might be what Disney used back then. (The one referred to as the "copper banana" Motorola Motrac part anyway)

Useful search terms

Recreation

The design of the recreation is essentially to take an audio track, amplify it, and drive an electromagnet. That electromagnet will affect one side of a ferrous tuning fork. The tuning fork will only resonate at its defined frequency, and possibly harmonics.

The other side of the tuning fork will have a similar electromagnet, possibly the head from a cassette player. The signal there will get amplified and filtered to provide an on/off signal.

An alternative for the other side is to have a reed switch there that gets affected by a magnet attached to the tuning fork, or perhaps by the tuning fork itself. That can directly switch an output then. (And filtered via debounce circuitry or RC circuit to convert the 'vibratey output' to a simple on/off signal.

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