Processor Clock Oscillator Crystals

Calculating crystal loading resistance.

Andre Abelian [engelec@EARTHLINK.NET] says:

1. connect 1k pot serially.
2. you need a scope to measure the sinusoid signal.
3. you must know that in the probe you have a capacitor about 15-45 pf when you probe it will add that value to it and it may shift the wave form
4. if you can not get a probe without the cap in it then use 2 same probes by connecting on both crystal pins this way it will add equal values on both crystal pins witch is much safer or if you already know the value of your probe add an other cap on the other side.
5. slowly turn the pot until you get sharp signal
6. once you got good signal check the value of the pot and match with closest resister you can get a few ohms + - may not even affect .

I did this once using 4 mhz crystal up to 200 ohms I didn't even see any changes. I ended up with 820 ohm.

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