Sorting quartz crystals by frequency - Page 1
Forum section: electronics / projects

author: smoothVTer
author_rank: Regular Contributor
timestamp: October 19, 2017, 12:40:38 pm
content: Situation: you have a qty. of 1000 quartz crystals, all the same part number, all are 4.0000 MHz +/- 20 ppm frequency tolerance. You have calibrated frequency counter with a known tolerance to 100 ppb. How would you set up a system to bin these crystals according to frequency?How would you drive the crystal?Do there exist frequency counters with built-in oscillator drivers, or would you have to build your own?If you were to build your own, what topology of driver would be least affected by temperature?

author: wraper
author_rank: Unknown
timestamp: October 19, 2017, 12:52:05 pm
content: Why do you want to sort them and where they'll be used?

author: LaserSteve
author_rank: Super Contributor
timestamp: October 19, 2017, 02:23:19 pm
content: There are standard oscillator circuits used by ham radio operators for sorting crystals for SSB filters. Start there. Frequency is not the only characteristic to bin for.Steve

author: tszaboo
author_rank: Super Contributor
timestamp: October 19, 2017, 02:24:55 pm
content: I would use a complex system called "intern" to do it. Probably make a small jig with a zif socket and 2-3 NOT gates, one to drive it, one to buffer it. One end is a simple USB cable, to power it, the other is a coax to the counter. The intern (preferably called Joe, or similar) would operate the jig and bin the components.

author: retrolefty
author_rank: Super Contributor
timestamp: October 19, 2017, 03:45:35 pm
content: The suggestions so far are useful mostly only for the matching of crystals to some desired desired PPM match. The actual frequency can only really be determined by measuring it when used in the actual circuitit's going to be used in.

author: LaserSteve
author_rank: Super Contributor
timestamp: October 19, 2017, 07:00:26 pm
content: Unless you have a signal generator with resolution of a few Hertz, you should have a look at the G3UUR method.Steve

author: smoothVTer
author_rank: Regular Contributor
timestamp: October 19, 2017, 07:30:52 pm
content: Thanks for the suggestions, guys & gals.I did not know about the G3UUR until today, I will give it a try.I understand about the crystal being affected by the context it is used in. In my case, it is used as a uC external oscillator between XIN and XOUT pins, with appropriate load capacitances per the datasheet. I plan to replicate the uC's pin capacitance in the test setup, along with load caps on each crystal pin.

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: October 19, 2017, 08:36:05 pm
content: I'd plug it in to the actual uP and see if I could pick up the frequency with an inductive pickup or at some test point. Test Rule #1- Test it the way you use it.

author: texaspyro
author_rank: Super Contributor
timestamp: October 20, 2017, 06:26:48 am
content: Plug it into a board that uses that micro. Program the micro to use a counter-timer output to output a signal to a pin which is derived from the crystal. Measure that frequency with a good frequency counter (preferably with a GPSDO or OXCO timebase).You can't probe the crystal pins directly... that will shift the oscillator frequency.I once sorted through 100 10 cent 16 MHz crystals from China looking for a "good" one. Total waste of time. They were all basically identical... and surprisingly good.

author: Mr. Scram
author_rank: Super Contributor
timestamp: October 20, 2017, 11:09:10 am
content: Quote from: NANDBlog on October 19, 2017, 02:24:55 pmI know it's just a joke, but please don't give interns just the shit jobs. Giving them some is fine, because every occupation has shit jobs that need to be done. However, an intern should learn about all the facets of the position, not just serve as an unpaid shit job jockey.