Quartz Crystal Testing

[s_elias]

Hi,

Interested in opinions on the best way to test Quartz Crystal on modules, without having to remove the crystal from the module.

What has worked for other enthusiasts in the past to verify the crystal is working? I know some people actual remove it from the module and test with another functional module.

Can anyone recommend an inexpensive frrequency counter to test with as well?

I recently picked this little scope up thinking I could use it for module troubleshooting some how? -> http://www.seeedstudio.com/wiki/DSO_Nano_v2

Here's additional reseach I came across.

right ways to test a crystal: -

(a) Using Oscilloscope (not sure if you need a 10x probe, otherwise you would load the crystal down?)

A crystal produces a sine wave when excited. It is appropriate then, to see a waveform representative of a sine wave on the clock pins. If the clock is not functioning properly, replace the crystal. In most cases this should solve the problem since microprocessors are usually very reliable. Check the crystal with power on.

(b) Frequency Counter (seems people in the forum are using this method)

Frequency Counter can be use to check the frequency of the crystal. The reading must be taken when the equipment power is switch "on". Place the probe of frequency counter to the crystal pin and read the measurement. Be sure that your frequency counter meter has the range that is higher than the crystal frequency you are measuring.

(c) Crystal Checker (has anyone built and used this with success?)

With this method, usually the crystal is placed in the feedback network of a transistor oscillator. If it oscillates and the LED is lighten up, this mean that the crystal is working. If the crystal doesn't work, the LED stays off. Instead of using LED, some other crystal checker uses a panel meter to indicate if the crystal is working or not.

[s_elias]

I was also inspired by this article on testing with a hand-held scope.

Half-way down the article - the author is checking the crystal.

http://ledwatch.net/_wsn/page4.html

[s_elias]

Purchased an Extech true RMS DMM Model 430 for $35. It has a diode, cap, temp. and frequency modes. Perhaps I can measure the clock from the crystal or output from the the microcontroller.

Also purchased a few ladies LED working watches for tinkering. Let the testing begin ! (Yes - I have my LED watches but don't want to mess up the working ones)

[Ole Joe]

Purchased an Extech true RMS DMM Model 430 for $35. It has a diode, cap, temp. and frequency modes. Perhaps I can measure the clock from the crystal or output from the the microcontroller.

Also purchased a few ladies LED working watches for tinkering. Let the testing begin ! (Yes - I have my LED watches but don't want to mess up the working ones)

As a word of caution, when a DMM, O'scope, Frequecy counter or other type of test
equipment is connected directly to either terminal of a watch modules quartz crystal,
a good working crystal may actually stop working. The reason for this is that the
added stray capacitance from the test equipments test probes "loads" the crystal
so much that the oscillator circuit in the integrated watch circuit will cease
to operate. As a general rule, if the quartz oscillator in a module is operational,
you will see some activity from the display when the various command buttons are pressed.
Sometimes, an indication that the crystal is bad is when a single digit of the display
is shown and is brighter than normal. Pushing the command buttons will have no effect
on the display. LED watch displays are multiplexed, i.e., the digits of the display
are turned on an off one at a time at a high frequency so that the eye seems to see a
display which appears to be on at all times. The multiplexing of the display is dependent
upon the quartz crystal oscillator being operational. No oscillator, no multiplexing,
no digit change or display at all. Quartz crystals made for watches in the '70's were
were quite fragile. It was easy to break the internal thin wafer wafer of quartz just by
dropping the crystal or watch from just inces. At that time, making crystals to oscillate
at 32.768KHz in small packages was state of the art. About the only sure way to test the
crystal is to pull it from the module and insert it in an external test fixture.
Hope this helps.

Joe

[s_elias]

Thanks Joe,

I was afraid of that, maybe I need high impedance probes, will that help?

Is there normally a clock out from the microcontroller that I could use as a test point, running at a lower frequency?

Also any ideas on diy external test fixtures for crystals?

I guess I would have to desolder the crystal and insert it into a "test bed" - but what?

I know some people have rigged up other "working" modules and simply use that.

Any other ideas like building a small test circuit with a flashing led which is dependent on the crystal?

[Old Tom]

The usual way of testing a 32768Hz (and 16368/8192Hz) crystals is to listen for the ultrasonic acoustic output from the crystal- they are really quite "loud", its just that the signal is beyond normal human hearing. Practically all watch rate machines function in this way. To build a tester you would need a very small piezo disc to use as a contact microphone, an amplifier with gain of about 5000, a squaring circuit to produce a square wave and a divider (say by 16 to give 2048Hz) which you feed to an earpiece/speaker. If the crystal works you get a squeak out of the speaker!

[Ole Joe]

The usual way of testing a 32768Hz (and 16368/8192Hz) crystals is to listen for the ultrasonic acoustic output from the crystal- they are really quite "loud", its just that the signal is beyond normal human hearing. Practically all watch rate machines function in this way. To build a tester you would need a very small piezo disc to use as a contact microphone, an amplifier with gain of about 5000, a squaring circuit to produce a square wave and a divider (say by 16 to give 2048Hz) which you feed to an earpiece/speaker. If the crystal works you get a squeak out of the speaker!

Tom,

Very clever idea, I've never heard of this technique. I've got to try this method out. Always looking for unique solutions
to nasty problems. Thanks for posting.

Joe

[s_elias]

Hi Tom,

That's a neat idea - I like it because it wouldn't be intrusive to the crystal as pointed out earlier in the thread.

I have a piezo already that I used as a DIY acoustic guitar pickup to an amp.

I'll have to run a few tests this weekend - it would be a nice addition to the DIY watch module tester as well

[s_elias]

Update from Friday's lab test -

I've had limited success obtaining a reading on my new DMM /w the frequency measurement and with my new pocket scope as well from a working module.

Things are looking promising, however the biggest problem is maintain a power connection to the module while working on it.

Back to the DIY module tester idea. I need some sort of clamp to get power to the module with the ability to work on the front / or back as needed.

Perhaps a clamp on a swivel /w a spring loaded contact plate to the pads - hmmmmmmm

[LED]

Well - isn't that how common watch Analyzers work? Accoustic probe, see excerpt from a Pulsar Analyzers diagram below:



Also you may consider that quartz crystals hardly ever fail completely. They may drift out of adjustment range but in a totally dead oscillator from my experience by 99% the culprit will be found somewhere else in the oscillator circuit.

[Ole Joe]

Well - isn't that how common watch Analyzers work? Accoustic probe, see excerpt from a Pulsar Analyzers diagram below:



Also you may consider that quartz crystals hardly ever fail completely. They may drift out of adjustment range but in a totally dead oscillator from my experience by 99% the culprit will be found somewhere else in the oscillator circuit.

Some analyzers work by detecting the electromagnetic radiation emitted by the quartz crystal oscillator of the module. I have an old
Valpey-Fisher A-600 analyzer that works using this method. Output of the unit connects to a frequency counter to display the oscillator
frequency for tuning to precisely 32.768KHz. Here's an excerpt from Patent #4078420, issued on March 14, 1978.

"The present invention is directed to a wristwatch analyzer of the same general type as that in U.S. Pat. No. 3,892,124, but one which has increased sensitivity for sensing the lower energy levels of the smaller timepieces and one which presents a digital display for ease of reading. In the present invention the operating light emitting diode wristwatch is placed face down on the test instrument or analyzer. Electromagnetic energy at the frequency of the watch time base passes through the viewing window of the watch where it impinges upon a disc-shaped antenna or a pick-up probe imbedded in the instrument support. The frequency of the time base is detected and displayed so that the frequency of the watch, if necessary, may be adjusted to come within the desired tolerance. Variations from the desired frequency of as little .+-. 0.1 second per month can be detected and indicated."

Joe

[s_elias]

So is this basically the "ultrasonic" noise coming from the quartz crystal vibrations we're discussing eariler in the thread?

If we take an ultrasonic pickup tuned to that frequency range and place the watch face down on it - in theory would it work? I guess this is similar to the "bat detectors" people are building.

Any schematics with the old tester available?

[Ole Joe]

So is this basically the "ultrasonic" noise coming from the quartz crystal vibrations we're discussing eariler in the thread?

If we take an ultrasonic pickup tuned to that frequency range and place the watch face down on it - in theory would it work? I guess this is similar to the "bat detectors" people are building.

Any schematics with the old tester available?

Electromagnetic radiation is different than the ultrasonic wave coming from the quartz crystal. Electromagnetic radiation is like a radio signal emitted from a radio stations transmitter antenna through free air. Ultrasonic waves are generated by the actual bending and flexing of the quartz crystal. I suppose that the waves generated by the bending of the quartz crystal, bounce around inside the metal container and produce the minute flexure of the can, which in turn is transfered to the piezo pickup.
Like I stated earlier, I was not aware that some analyzers use the ultrasonic method of detection until Ole Tom mentioned it in an earlier post. It certainly would be fun to experiment using that method . I would think, that in order to accomplish a viable method of detection, that the piezo pickup itself should have a natural resonant frequency of around 32KHz for maximum sensitivity, followed by a fairly sharp 32KHz bandpass filter, and as Ole Tom stated, "lots of gain".
I do not have a schematic of a tester like the one I have. For sure it has lots of "gain" and a very narrow active band pass filter made up of about 10 stages of 32.768KHz crystals and op-amps. The Valpey-Fisher will pickup a signal from about 3" away from the sensor and yield a rock solid signal to the frequency counter.
Joe

[s_elias]

Wow - Thanks Joe for the details on the tester.

Sounds like that would be interesting to research further. (Radio wave detection) I wonder if the modern portable radio frequency scanners would pick up the signal in the watch.

Interesting thread, I'm learning lots from you guys - thanks for sharing

[s_elias]

Hi,

Back to this topic - has anyone ever used this to test if the crystal needs replacing -> Bergeon 6437 Quartz Watch Test Pencil?
http://www.esslinger.com/bergeon-quartz ... encil.aspx

As far as I can tell, it's a pen with a quartz crystal glued in where the ball point would be with leads sticking out

Just wondering if anyone has used them in the past and if they work as a quick check when looking for "bad" crystals.

I have an old black disposable papermate felt pen that I might donate for tonight's cause -> diy quartz crystal test pen. Snip off the end, remove the ink, glue in a crystal with leads sticking out, reaply the cap. Ta Da