Electronics > Projects, Designs, and Technical Stuff

I want to build a crystal tester. Will this work?

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james_s:
I have one of these: https://www.ebay.com/itm/DIY-Digital-LED-1Hz-50MHz-Crystal-Oscillator-Frequency-Counter-Meter-Tester/252957151186?

It's not the most amazing thing ever but it does work fairly well and the cost is very little. It has been a handy gadget to have on my bench.

edavid:

--- Quote from: james_s on November 29, 2019, 07:38:36 pm ---I have one of these: https://www.ebay.com/itm/DIY-Digital-LED-1Hz-50MHz-Crystal-Oscillator-Frequency-Counter-Meter-Tester/252957151186?

It's not the most amazing thing ever but it does work fairly well and the cost is very little. It has been a handy gadget to have on my bench.

--- End quote ---

That uses a single transistor oscillator... I found that with the supplied capacitors (which might vary by seller?), it didn't start with crystals below about 4MHz.  Of course you could tweak that, but then maybe it would stop working with high frequency crystals.

It definitely doesn't work with tuning fork crystals.

DaJMasta:
Do you have a signal generator?

A crystal is a very tight bandpass filter, so if you sweep one input with a signal, the maximum output on the other pin signal level appears at the crystal's resonant frequency.  I would stick to lower power levels because, as mentioned, normal crystals are not rated for much power, but you should be able to tell accurately where its frequency lies just by monitoring output power/voltage provided you terminate the line after the crystal.

james_s:

--- Quote from: edavid on November 29, 2019, 07:52:45 pm ---That uses a single transistor oscillator... I found that with the supplied capacitors (which might vary by seller?), it didn't start with crystals below about 4MHz.  Of course you could tweak that, but then maybe it would stop working with high frequency crystals.

--- End quote ---

I'm not actually sure that I've tried it with anything under 3.58MHz, mine worked fine with that. Shouldn't be too hard to add multiple ranges or as cheap as it is, build a few of them to cover other frequencies. Or just build an improved one yourself based on the basic concept.

rhb:
A single transistor Pierce oscillator with provision to adjust the xtal drive should handle anything for a basic functional test.  Add a voltage follower buffer followed by an ebay log detector.

A nanoVNA will show you as much detail  about the serial and parallel resonances as you could ever wish for under $50.

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