I was looking for some ideas on a circuit to test some crystals i have laying around just plug one in and read it with a counter or my scope.

 

I was looking for some ideas on a circuit to test some crystals i have laying around just plug one in and read it with a counter or my scope.

If you have an MCU laying around it might be of help, some of them will output the crystal's frequency on one of their pins, like the AT89LP4052.

You could just breadboard the MCU and connect each crystal to it using jumper cables. See what happens at the output pin.

 

I thought about that been looking at a pierce oscillator. Maybe the uC be the best way to go.

 

I thought about that been looking at a pierce oscillator. Maybe the uC be the best way to go.

Pierce oscillator is pretty easy. Which frequency are the crystals?

http://www.crystek.com/documents/appnotes/pierce-gateintroduction.pdf

 

There all different most you can't read there value.
I was just thinking about some why to free run them so I fine out manly the watch ones maybe 32768 Hz but they are not marked.

 

There all different most you can't read there value.
I was just thinking about some why to free run them so I fine out manly the watch ones maybe 32768 Hz but they are not marked.

Most modern MM's can read frequencies of up to 20 MHz ... maybe you don't need an oscilloscope at all

 

This is for Testing faulty crystals.
Write a program to generate frequency output.
for example, Generate freq. such that 12MHz crystal time base will give approx 12KHz o/p. measure o/p on DMM.
now replace the crystal with different values and you will get the corresponding freq. output in KHz.

e.g.

CRYSTAL KHz o/p on jig

24MHz 24.41KHz

16MHz 16.27Kz

12MHz 12.20KHz

11.0592MHz 11.25KHz

10MHz 10.17KHz

4.096MHz 4.16KHz

4.000MHz 4.07KHz

BEL 4433.619KHz 4.51KHz

4194.304 4.27KHz

 

There is no one-size-fits-all.

Crystals are made differently for different frequencies and applications.
There are series resonant and parallel resonant crystals.
Crystals have specific impedances and require a given range of loading capacitances.

Low Frequency (LF), HF and VHF crystals are cut and made differently.
There are fundamental resonance crystals and harmonic resonance crystals. Many HF crystals must be used at the third harmonic.

For starters, specify the range of frequencies for which you suspect the crystal was designed to oscillate.

 

For simple, I do as @cmartinez suggests in post #2. In fact, for LF crystals (e.g., 32.768 kHz to 60 kHz -- I have not tried higher freq's) most PIC's allow you to use two oscillators. The chip's main oscillator in effect can count the second oscillator. Of course, the Pierce oscillator is also simple. The PIC input simply provides a free inverter.

John

 

W2AEW has a video on a crystal tester. I think this is it:

 

http://www.robkalmeijer.nl/techniek/electronica/radiotechniek/hambladen/qst/1990/01/page21/