This2 Channels IR Reflective Sensors(TCRT5000) includes 2 professional digital IR reflecitive sensors and a mainboard to handle the 2 channel signals. These sensors can detects tiny line and is suitable for line finder such as helping a robot car folllow a black line on white background or vice versa. You can also adjust the potentiometer on the mainboard with a crosshead screwdriver to adjust the measuring range.

The infrared diode will emmitting the infrared continutelly when the module connect to the power, when the emitted infrared light has not been reflected or the strength is not big enough,the triode will in the off state, at this time, D0 output logic LOW and the signal indicate LED off.