Hey everyone, I'm doing a small on-my-own project to build myself a binary clock. Since I haven't personally learned anything about crystal oscillators in any of my EE classes yet, I had to use someone else's design for this part of my project. The circuit I used was this:
http://hackersbench.com/Projects/1Hz/
I understand all of his circuitry here except the crystal oscillator, which has me a bit confused as to how these things work, and why it's set up in this configuration. From my understanding about crystals, is that it's function is very similar to a RLC circuit, without being a RLC circuit (obviously). I noted when I bought the "tuning fork" as many websites refer to it is, that the component itself was rated for a very small capacitance, which I presume has an effect on the stability of the oscillation pulse.
The other thing to note, in my physical build of this circuit (minus the ICs), is that I used values that are definitely going to be off what he suggests; for instance, I bought 22pF capacitors as I couldn't find any 33pF. I didn't have any 6.8M resistors, so I put a series of resistors to make a near-equivalence of 13.6 (I think it's actually 13.2M now that I think about it). Anyway, my point in sharing this is that it doesn't appear to have an effect on the stability of the clock pulse. I have the signal being divided down to 1Hz, and comparing it against a timer I know is accurate (for all intents and purposes), it seems to be pretty darn accurate. If I had to give a theory on why these resistors and capacitors are these sizes, I'd imagine it has something to do with a fairly specific voltage and a very small current (in the hundreds of nano amps from a quick calculation).
So anyway, long story short; how does resistance and capacitance ratios affect crystals, and why must it be in this kind of configuration for my application?
Thanks!
http://hackersbench.com/Projects/1Hz/
I understand all of his circuitry here except the crystal oscillator, which has me a bit confused as to how these things work, and why it's set up in this configuration. From my understanding about crystals, is that it's function is very similar to a RLC circuit, without being a RLC circuit (obviously). I noted when I bought the "tuning fork" as many websites refer to it is, that the component itself was rated for a very small capacitance, which I presume has an effect on the stability of the oscillation pulse.
The other thing to note, in my physical build of this circuit (minus the ICs), is that I used values that are definitely going to be off what he suggests; for instance, I bought 22pF capacitors as I couldn't find any 33pF. I didn't have any 6.8M resistors, so I put a series of resistors to make a near-equivalence of 13.6 (I think it's actually 13.2M now that I think about it). Anyway, my point in sharing this is that it doesn't appear to have an effect on the stability of the clock pulse. I have the signal being divided down to 1Hz, and comparing it against a timer I know is accurate (for all intents and purposes), it seems to be pretty darn accurate. If I had to give a theory on why these resistors and capacitors are these sizes, I'd imagine it has something to do with a fairly specific voltage and a very small current (in the hundreds of nano amps from a quick calculation).
So anyway, long story short; how does resistance and capacitance ratios affect crystals, and why must it be in this kind of configuration for my application?
Thanks!