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