James Newton, webhost wrote:
> Two photo-sensitive inputs. Input will be sensitive to low audio
> frequency pulses of light, rather than steady light levels. One LED
> output.
>
> With no input, the output flashes at a "rapid" but visible rate
> (1KHz?).
>
> If only one input is active, there is no change in the output.
>
> As the input frequency increases, assuming both inputs are activated,
> the output frequency decreases.
>
> When both inputs are receiving "rapid" (1KHz?) pulses, the output is
> completely suppressed.

I still don't see how the frequency of both inputs together is supposed to
control the output frequency.  For example, if one input is 1KHz and the
other 10Hz, is the output supposed to flash fast, slow, or not at all?

In any case, this sounds like a job for a PIC like a 12F629.  It sounds like
you don't need much accuracy.  The main loop constantly checks timer 0 and
updates how long it's been since a pulse was seen on each input.  When a new
pulse is received or the time gets above a threshold, the official pulse
period for that input is updated.

I don't understand the function that takes the two input pulse periods and
decides the output pulse period, but whatever it is doesn't sound too hard
to write in PIC firmware.  A timed interrupt is used to toggle the output.

This isn't an analog problem at all except the input detector that
thresholds the analog light level.

This sounds too easy.  What am I missing?


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