picking up watch freqency

[steve_lowestoft]

Hi I looking into trying to checking the frequency of the oscillator in watches that use crystals around 32kHz without opening the case its the front end where I have a problem with any ideas.

 

[k7elp60]

I'm not sure what information you are looking for. The clock frequency is more than likely 32.768khz.

 

[steve_lowestoft]

Hi yes the clock frequency is more than likely 32.768khz but what I want to do is check this frequency without openen the case eg receive the frequency via a wire loop and ampifie it or somthing then i can feed it into a pic to check the frequency.
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[Sceadwian]

That seems like a very strange thing to do. Considering the amount of power a watch crystal uses in the first place I doubt it puts off a detectable amount of RF energy.

 

[morningside]

I presume you are a watchmaker? I remember a few years back my father had such a device that done analogue as well as digital watches. From what I recall the watch was placed on a tray and had a tuned radio (RF) antenna picked up the transmissions.

 

[Rolf]

I presume you are a watchmaker? I remember a few years back my father had such a device that done analogue as well as digital watches. From what I recall the watch was placed on a tray and had a tuned radio (RF) antenna picked up the transmissions.

I know of a watchmaker that specialize in the old watches that used a tuning fork for the freq. standard. The device had a microphone that heard the frequency and amplified it and beat it against a standard (I don't know what).
That is about all I remember about the device.
To detect the minute amount the RF in a metal encased enclosure might be difficult but I think there should be a good chance if the back was off the case.
However it should not be to difficult to make a phase comparesen between the one second audio beat and the one second beat of an atomic clock.

 

[morningside]

Hmmm. Thinking about it must have been (for digital) a rf receiver with a very high gain front end with a bit of filtering connected to a frequency counter.
You are right about the analogue side of things but I do remember the watch laying on a tray.
The resultant display was given as drift in seconds NOT frequency and part of per day. I presume the makes it easier to tune (for the layman) than saying 32.764434234 KHz
As well as the quartz digital ones what about the tuning-fork version? I presume the all resonate at 32.768 KHz and divided to give 1 Hz

 

[steve_lowestoft]

Hi

Yes you correct its for digital watches in plastic cases one of my mates work with watches and want to check the frequency of the oscillator without opening the case. I said I think about it and I believe the problems are in 2 parts.

1 how pick up the oscillator frequency .

2 display results.

I know I can design a frequency counter and display the results in the required format using a micro eg. a pic but the front ends the problem.

Any ideas

steve

 

[Rolf]

Hi

Yes you correct its for digital watches in plastic cases one of my mates work with watches and want to check the frequency of the oscillator without opening the case. I said I think about it and I believe the problems are in 2 parts.

1 how pick up the oscillator frequency .

2 display results.

I know I can design a frequency counter and display the results in the required format using a micro eg. a pic but the front ends the problem.

Any ideas

steve

Are you talking about watches with analog displays?
If so you might use the one second tick to trigger (through a mike & amp) a counter in the "periode mode". I dont know if this would give you the requierd calibration accuracy but theoreticaly it should be possible. It would certently be a lot simpler.

 

[steve_lowestoft]

Hi

No the watches have digital display its not going to easy but if can pick up the frequency the rest is no problem

steve

 

[Rolf]

I guess........

Hi

No the watches have digital display its not going to easy but if can pick up the frequency the rest is no problem

steve

I guess you have to experement. Make a coil (156uH) large enough for the watch to fit inside, paralell it with 156nF (it should resonate at a little over 32Khz) and follow it with a high gain op-amp. Look at the output with a oscope. This should tell you if it is possible detect the osc freq.

 

[steve_lowestoft]

Thanks I will give it a try.

steve