This reflection IR sensor is a simple plastic housing with two elements - an IR LED and an IR phototransistor. You can control the IR LED and turn it on to bounce the IR objects to determine their reflectivity. White and light-coloured objects bounce the light so that you can detect it. Black and dark objects absorb infrared light so that it is not detected. Similarly, if something does not interfere with the sensor, it will not trigger either.

These sensors are useful when you want to detect if something has passed in front of the sensor. If the encoder wheel has black and white stripes, the photodetector is fast enough to indicate the number of revolutions per minute. The most common use of these sensors is for line tracking robots, they are so small and easy to weld, you can assemble them very close.

This sensor is compact, user-friendly and easy to weld. It even has practical markings on the plastic so you know which side is the LED and which side is the output of the phototransistor. We do not include resistors 470Ω -1KΩ for the infrared LED, nor 10KΩ for the pullup output. But you have a package of 5!

This works best when you detect a light-colored object at a distance of about 5 mm - 2 to 10 mm worked quite well, but your results may vary depending on the brightness of the LED, the brightness of the object, etc.