I think you're looking for a schmitt trigger, but IIRC the a lot of the PIC
inputs have schmitt triggers already built in.  Check out the I/O-port
diagram/descriptions in the datasheet.

Cheers,
-Neil.



richardv2 wrote:
> 
> I want to signal condition a phototransistor line sensor output to a
> digital input.
> 
> Although I am using the PIC16F8680 chip, the answer should be valid for
> most PIC chips. If not, please let me know.
> 
> I have designed, built and tested a bank of 8 IR Transmitter/
> Phototransistor pairs.
> They all return 1.2 to 4.2 volts at 3/8ths inch depending on a light or
> dark surface below the sensors.
> 
> I ultimately want an 8-bit digital pattern where the sensors might react
> like this when travelling over a black line.
> 
> 00011000
> 00001000
> 00001100
> 00000100
> meaning the robot is drifting off center.
> 
> Seems like I have several options:
> Lets say I use Port B as an input port.
> 
> 1. If I just run the sensor inputs to the port, it would seem that I would
> get what I want; zeros or ones. 
> 
> 2. Could I send the 1.2-4.2 volt signal through some kind of chip like an
> inverter to "clean up" the signal and only produce 0 or 1? I know an opamp
> could do this, but that seems like overkill.
> 
> 3. How about an LED/resistor voltage divider to drop the 1.2 down to 0.7
> to make sure I get a zero into the chip at low voltage??
> 
> 4. I could use ADC, but it seems inefficient to convert the voltage into
> an 8 bit number just to turn it back into a one or zero.
> 
> So what would you do???
> 

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