Re: Watch Crystal dissipation

osr@xxxxxxxxxx wrote:
> For a microscope system here at the university I need to monitor the
> energy used by a oscillating 32Khz watch crystal, anybody have a clue
> how to do that and keep the waveform sinusoidal? I'm looking for
> papers or sample schematics on leveled crystal oscillators with some
> form of AGC volatge that can be monitored. I need to measure around 800
> microwatts at a 10 microwatt resolution without disturbing the
> oscillation frequency, and no a scope probe across the cystal wont do,
> I need a voltage to a A/D for feedback.

Hmm.
32Khz.

I notice that 96Khz soundcards are getting cheap.
I wonder if at that sampling rate, they will work up to nyquist.
If so, 32Khz wouldn't really be a stretch.

Simply output a 32Khz tone on one channel through a largish resistor, with
another channel monitoring the amplitude (through maybe a FET probe stuck
next to the crystal).
Latency will suck, I'd be surprised if you could close the loop at better
than 10Hz.

.

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