It is an IR phototransistor not a photodiode, so I didn't think I would
need amplification, just a pull up resistor.  But the output at the
collector then doesn't seem like it will work very well with a ST input
because it takes a long time for the output to rise back to 5 volts after
it is exposed to IR.  I have it setup as a 10k resistor connected to +5V
and to to IR phototransistor collector, with the emitter connected to
ground.  I've put the Vcollector on the oscilliscope, and have been able
to see signals from a IR transmitter by triggering on a negative going
edge.



On Fri, 2 Jul 1999, Andy Kunz wrote:

> >via a single I/O pin.  What is a cheap way to do a little conditioning on
> >those sawtooth waves.  I am going to be implementing 1200 baud UART in
>
> Use a PIC with built-in comparator, or use the ST input pins.  If you're
> looking at the raw data, you need an amplifier of some sort.
>
> Have you thought to connect the diode across the inputs of an op amp, with
> a large resistor for feedback to the neg side?
>
> Andy
>
> ==================================================================
> Andy Kunz               Life is what we do to prepare for Eternity
> ------------------------------------------------------------------
> andy@rc-hydros.com      http://www.rc-hydros.com     - Race Boats
> andy@montanadesign.com  http://www.montanadesign.com - Electronics
> ==================================================================
>