ir sensors for black and white block detection

[abacusdheda]

i want my bot to detect a block like this(see attachment)
at a range of 20 to 25cm . so what sensors i should use for IR transmitters(TSOP or simple IR sensor)??
do TSOP detect black & white?

[codename25]

I think IR sensor is enough..Because black color absorbs the IR radiation and white color reflects ,this makes the IR sensor to identify Black & white.

[Soeren]

Hi,

With IR, you need to assert that the black is still black, as lots of black stuff is "the new white" when using IR light.

I don't think that you will have that much luck using IR-LEDs and integrated receivers, as this combo will be quite wide eyed.

A simple red LASER pointer (modulated perhaps) as the source and a (wide eyed) photo transistor, OR, a wide beamed LED and a phototransistor with a narrow angle of detection (either ready made or with DIY optics) would be the way to go.

Using visible light will make it so much easier to test and align it as well - and it will adhere to the 70's hit: Black is black.

At 20cm distance, the black part is a maximum of 14cm wide (if rotated so a corner is pointing towards the detector) but still only 5cm in the vertical direction - this takes one of the devices to be a rather narrow beam (photo transistors with a 5° angle should do nicely).

[abacusdheda]

@soeren: thanks for your insight on geometrical aspects of the sensors. i shall consider using lasers, depending upon availability.

@codename25: to bolster your argument, i can use two LED-sensor pair, aligned vertically, so that difference between their values will suggest me the presence of the block.