Electronic clock pulse generated from wrist- or pocket-watch

[tallphil]

Hi, I'm not sure whether this is the best place to post this question, but hopefully someone can either give me some help or suggest where a better place to ask would be.

Friends and myself are building a mechanical and electronics based project, with a certain steampunky aspect to it. We would quite like it if the clock signal required by the various electronics systems was generated somehow from the ticking of a wristwatch or pocketwatch, with the frequency of the resulting pulse multiplied sufficiently to be useful.

It would be important that the casing of the watch need not be breached - the watch should be able to be put in place, but also be able to removed when we want to.

My ideas so far have ranged from having an inductive pickup of the qwartz crystal in the watch to having a small imaging system detecting the motion of the second hand on the face of the watch; however my knowledge of electronics (whilst not too shabby) probably isn't up to the required level to do this on my own.

Obviously any solution cannot rely on the electronic production or use of a clock signal - that would kind of defeat the point.

Any help appreciated.

 

[Hero999]

Or you could use a small ultrasonic microphone to listen to the 32768Hz signal produced by the crystal.

But why bother? It's much easier to build an oscillator using a 32768Hz crystal.

 

[tallphil]

There are, of course, hundreds of easier ways to generate the clock pulse, but this is all about the flavour of it.

We want the whole system to work only if you've placed your wristwatch in it. It's silly, yes, but it's what we want.

Is that 33kHz signal a standard for qwartz crystal watches, do you know?

 

[Hero999]

It's 32768Hz, not 33kHz and is a standard frequency which has been chosen because dividing it by 215 will give 1Hz and is easy to do with a simple binary counter.

 

[tallphil]

Ah, very sensible. So I guess the next question is how to limit the response of a microphone to around this frequency, and turning its output into something resembling a square wave.

 

[Hero999]

Use an ultrasonic microphone with a suitable resonant frequency and a 32768Hz watch crystal as a filter. It should be pretty easy to square the signal with logic gates.