Electronics > Projects, Designs, and Technical Stuff
I want to build a crystal tester. Will this work?
technix:
The tester should allow me to test if a crystal works, and have a rough idea about its frequency. I wonder if this will work: build a simple oscillator out of one of the two gates in 74LVC2GU04, use the other gate as a buffer, then output the signal to an BNC connector. If I want to check a crystal, I can plug the crystal in, power the board from USB, and hook a BNC cable to my oscilloscope.
ChristofferB:
I dont see any reason why this shouldn't work I mean, I think this is pretty much the only way of making a crystal tester.
On ebay you can get tiny frequency counter modules very cheap. If you built one of those into your crystal tester you wouldn't even need the PC oscilloscope!
tszaboo:
And then the frequency changes with the parasitic and the different built-in capacitors.
edavid:
It depends on the frequency range you want to cover. It's hard to make a single oscillator that will start reliably with crystals over the whole AT cut range of say 100kHz-30MHz. If you can limit it to the more commonly encountered crystals of say 2MHz-24MHz, that will probably work.
Tuning fork crystals will need a separate circuit, otherwise you are likely to damage them with excessive power.
rhb:
It may be more elaborate than you want, but Chris Trask's crystal impedance tester is worth building.
http://home.earthlink.net/~christrask/
Bottom of the page under "The Solderwick Chronicles"
Crystal Impedance Test Set
You should at a minimum read the article.
Another option is to use a nanoVNA to measure the S21 response. I built a couple of versions of Trask's set, but never got around to interfacing it to an MCU to automate the measurements as I had intended. I think the nanoVNA sort of makes that concept obsolete. Subsequent to my work with Trask's design I bought an HP 8560A and 8753B/85046A before the nanoVNA burst on the scene.
A well made Pierce oscillator done dead bug style using short leads ought to work over a pretty wide range, though as noted, watch out that you don't overdrive the crystal.
Have Fun!
Reg
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