"Timegrapher" sensor for LED/LCD watches

[grenert]

Hi, all.

Testers for digital quartz watches (Seiko QT-77, QT-99) have a sensor to pick up the internal quartz oscillations and determine the frequency. How do these work? I know that conventional analog watches use piezo or other microphones, but I would think these wouldn't work for a watch without any moving parts.  Anyone know or have circuits/service schematics that show the design?

Thanks!

 

[praezis]

In fact they use piezo microphones, as 32kHz is near the audio frequency range. The faint signal is amplified, sent through a narrow 32 kHz quartz filter, amplified and ....

Frank

[grenert]

Wow, that's pretty amazing! I'll have to do some research on ultrasonic piezo microphones.

If anyone has schematics of commercial models, please post them.

Thanks!

[JohnR725]

Some use what they call capacitive pickup. If you look at the witschi timing machines they'll claim inductive/capacitive usually on one pad and then they have a piezo On the other side.

13 hours ago, grenert said:

Anyone know or have circuits/service schematics that show the design?

Try doing a patent search you'll find some of the early electronic ones. Not the best way to build him though I heckuva lot of integrated circuits.

Then they give you an idea about sensors here's an image out of a manual for a witschi machine. The acoustical is a protruding metal pin that goes down to a piezo Pick up. Then the capacity of not clear what that is because it's hidden from view and then on the other side there were coils if I remember right interfere right cup course. I haven't taken one of these apart but  the past I had the taken apart my witschi  earlier version can't remember the model number and unfortunately I don't have any digital pictures. They used to act up and I'd have taken apart and see if I try to fix it which is able to do which is quite interesting considering they sand off all the part numbers. They really don't want you to know what's inside the machine. Which is silly because if you're a professional design engineer reverse engineering they make devices to read integrated circuits and tell you what they are or you just dropped the schematic and figured out for yourself. To just makes it a pain in the ass for someone trying to troubleshoot and repair the thing.

 

[praezis]

I just answered how 32 kHz quartz pickup works per question. Today however this is less important as inhibition comes into play. So the picked up quartz signal is changed in the dividing stage and does no more show the resulting rate.

The inductive pickup catches the motor pulses (1/sec or less) which do show the rate.

The capacitive pickup catches the display frequency of digital watches and also the 4.19 MHz quartz frequency formerly used in clocks.

Frank

Edited December 3, 2022 by praezis