Stephen Brown wrote:
>
> Hi,
>
> I'm interested in measuring the frequency of a pretty clean sine wave
> (output from a switched cap (not to narrow bandwidth) bandpass filter)
> using a 16c84. This is for a musical instrument tuning
> application. Presumably I would need a 0-5v square wave coming into the
> pic for a frequency counter routine. Any ideas on the best way to
> convert a sine wave to a square wave for this purpose
> (e.g. comparator, overdriven amplifier, PLL)? I played around with a
> LMC568 PLL circuit to lock onto the sine wave signal and output a
> pulse train, it works but the problem is that the lock in frequency
> range for this device is +-60% of the center frequency -- too narrow
> for this application. Ideally, I need to be able to handle a bit more
> than an octave above and below 440 Hz (i.e. about 200Hz-1000Hz). The
> CD4046 ??  PLL chip can be configured for a much wider range, but it
> is my understanding that it needs a square wave input itself (am I
> wrong?). The nice thing about these PLL things is that they can create
> a logic signal indicating when they are locked onto a frequency signal
> -- i.e. they can tell you when a valid input is there.
>
> Anyway, any hints would be appreciated.
>
> Steve Brown
>
> sbrown@ned.ara.com
> browns@sover.net


Why not simply drive it into a schmitt trigger inverter



Peter .......
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