AVR-Chat

One of the really nice things about the AVR processor line is that EVERY I/O
line is a schmitt trigger input.

By adjusting the load resistor of the photo-transistor, you should be able
to drive the AVR input pin directly.  Read the data sheet to see what the
thresholds are.  They are pretty well defined so your design will work from
chip to chip.

Cheers!


-----Original Message-----
From: Graham Davies

--- In AVR-Chat@yahoogroups.com, "Phil" <phil1960us@y...> wrote:

> with a photo transistor, you simply
> pull it low and take the output
> from the emitter.

I would think you'd need a comparator so that the input to the MCU
was a proper logic level and not some analog signal that could spend
a lot of time floating around between the thresholds.  Especially if
you're expecting it to generate an interrupt.