Best for a short informative paragraph on a tutorial site.
The IR LED emits a 38kHz–56kHz modulated signal (though many clones use continuous IR). The phototransistor detects reflected IR from an obstacle. The LM393 comparator compares the phototransistor’s voltage to a reference voltage set by a (blue box on the board). When reflected IR exceeds the threshold, the output goes LOW. fc 51 ir sensor datasheet hot