Crystal testing issues

[Murugesh_89]

Hi,
I am using a 10Mhz crystal for my PIC microcontroller. Every thing including timer,uart are working fine. But i just want to test the output frequency of crystal using oscilloscope. The scope showing a sine wave with the time period of 1 milli seconds which leads to a frequency of 1000 Hz. Why it showing like this?



Thanks,
Murugesh

 

[betwixt]

Assuming your oscilloscope has wide enough bandwidth to see 10MHz, the most likely reason is the scope probe capacitance is stopping the oscillator running properly. Remember that the loading capacitors around the crystal are very small in value and the probes themselves probably have much higher capacitance and appear in parallel with the real ones. If possible only measure at the output side of the oscillator as it will be less prone to loading than the input side.

If you really need to measure the frequency accurately, use a low-capacitance scope probe, preferably in x10 mode if it has it.

Brian.

 

[wp100]

Hi,

If your scope cannot handle that high a frequency, then make a simple program that toggles a port of the pic at a lower speed, say 1mhz, and then measure that on the scope and multiply its result by 10

 

[ZASto]

If you are so concerned on your crystal accuracy then read the following: https://www.romanblack.com/onesec/High_Acc_Timing.htm on how to test your crystal.