I have one working about 4mm using a ST input to a Picμ.
Max.

 

Does such sensor can tell the difference between red and white, or the difference of 1 mm height? Can you link me to a good par for this?

It might if you use a filter - the white background reflects all colours, if you can figure some way to use blue light - the red pointer will reflect less of it than the white background.

 

I tried it with very crude setup; blue 5mm LED @ 20 mA, Si detector, 1 mm wide X 7 mm long, white paper, & 1 mm red wire. LED & sensor angled about 30 deg. paper about 1 cm in front. Detected 1 mm wire moving back & forth. Worked about as well with white wire as it did with white LED. OK with real photo reflective sensor, K but spacing is critical, about 5 mm, & not as sensitive to wire movement.

 

I tried it with very crude setup; blue 5mm LED @ 20 mA, Si detector, 1 mm wide X 7 mm long, white paper, & 1 mm red wire. LED & sensor angled about 30 deg. paper about 1 cm in front. Detected wire moving back & forth. Worked about as well with white wire as it did with white LED. OK with real photo reflective sensor, K but spacing is critical, about 5 mm, & not as sensitive to wire movement.

Good job! I like it. Can you feed LED by pulse 1...10 kHz voltage and put signal from sensor through capacitor on input of any high gain amplifier?
EDIT: May be some astable multivibrator with LED in series with collector's resistor.

 

I believe that a modulated LED could be used but from what I saw direct detection with a comparator could work.

 

I believe that a modulated LED could be used but from what I saw direct detection with a comparator could work.

Using pulses may be necessary so that mains modulation from room lighting can be filtered out.

 

I believe that a modulated LED could be used but from what I saw direct detection with a comparator could work.

EDIT: Sensor pulse level shown after capacitor.

 

There were 5 LED lights on in celling when tests were made, no interaction.

 

There were 5 LED lights on in celling when tests were made, no interaction.

Turn ON-OFF incandescent bulb close to test area, then you will see big difference.

 

I have tried incandescent and florescent right above the QRE1113 with no effect.
Max.

 

I have tried incandescent and florescent right above the QRE1113 with no effect.
Max.

Max, I agree with you. QRE1113 contains 48% electro-optical efficiency infrared LED, and phototransistor, spectrally matched with LED. At very short distances illumination intensity from LED much more than any possible intensity from ambient light.
I had experience with design of reflective sensor for ceramic products on conveyer inside steel tunnel with infrared emitters, through quartz window on distance 300 mm. I used blue LED, photodiode + blue filter, both with lenses for focusing on product, but only after applying pulse current for LED I got desired stable results.