James Newton, webhost wrote:
> Analog design challenge: Build a NAND gate that is sensitive to
> /pulses/ (not level) of light from the cheapest possible components.
>
> ...
>
> Anyway, I really want to make a set of visible light (LED) NAND gate
> Lego blocks for my kids to learn from. And I don't want them to be
> light level sensitive, so I think that reacting to pulses (or their
> absence) would be best. Anyway, it makes it easier for inputs like
> motor shafts and optical interrupters, and easier for the kids to
> see. The common "is that LED on?" question is much less common when
> the LED is expected to flash or not.

I'm still confused.  You apparently want two light inputs that detect
flashing light?  The question then becomes how flashing is "flashing"?
Obviously there is a time element here since you need to decide on a minimum
valid frequency at least (I imagine you don't intend a day/night cycle to be
interpreted as flashing, although it is).  But the time element doesn't make
sense with "NAND", which is a simple combinitorial logic function.  Later
you said you wanted to know the frequency too.  Now I really don't
understand how to apply NAND to that.

You need to cut the hand waving and give us a clear spec.


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