Before you say google it... that's not what i'm thinking.
What if i did something like, output on pin 2 or 3 turn it off, and wait... would i get a voltage back from the voltage i sent it to? or an inverse voltage? is it even possible? is it possible to have any fun with crystals and arduino?
Yea it is but not quite as you envision. There is a great deal of knowledge required or some others shared work to do much with a crystal.
Consider "would i get a voltage back from the voltage i sent it to? or an inverse voltage?" Quoted from OP's original post, the there will be a return but it will only occur for perhaps as much as 1 or 2 cycles at the crystals resonant frequency for example with a 10 MHz crystal 2 cycles are too short to measure. Record or use yes but not measure accurately. It is much easier to use simpler devices can use the oscillator's characreristics (loading and voltage and temp) to control an oscillator and measure all the pertinent parameters from the response of a crystal much simpler as controller test programs are available for "Big' crystal MFr's. For a much simpler test replace it. This is based on your desire to measure something I took that basis because there is very little to be returned beyond some esoteric measurement beyond the capacity of an Arduino product. The 10 MHz example would generate 1.5 to perhaps 3.5 cycles (arbitray numbers but to scale) Little can be returned possibly but an estimate of the Q and the resonant frrequency.. Only estimates as there are a max of 350 nS to do the measurement.
Bob
would i get a voltage back from the voltage i sent it to?
You can always report it back.
An alternative is to put a probe on the pins while the oscillator is running. You will get a square output on the output pin and you will get a near sine wave on the input pin.