Infrared sensor has a frequency to activate it?
The 38kHz sensor (such as the Vishay series e.g TSOP1838) are designed for use with IR remotes and IR barrier type applications. They are designed to work with IR emitters that oscillate the IR at 38Khz and additionally modulate that frequency with lower frequency pulses. The sensor (receiver) is designed to have high gain at 38Khz and demodulates the signal. The demodulated output signal pulses can be directly decoded by a microprocessor. The main benefit is reliable functioning even in disturbed ambient light thus protecting against uncontrolled output pulses.