The sensor is highly dependent on the object's color and texture. Dark or matte black surfaces reflect less IR light and may be harder to detect than white or reflective ones.
Double-check your physical wiring against the standard FC-51 layout: fc 51 ir sensor datasheet hot
Sensor output stuck LOW (always detects). The sensor is highly dependent on the object's
delay(500); // Cool-down period
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: The FC-51 is designed for 3.3V to 5V DC . Connecting it to a higher voltage source (like a 9V battery directly) will cause the onboard voltage regulator or IC to overheat and potentially burn out.
If you are driving an external device, decouple it from the sensor. Connect the pin strictly to a high-impedance digital input pin on your MCU (e.g., Digital Pin 2). If you need to trigger a motor or relay, route the sensor output to your microcontroller code, and use a separate MCU output pin to control a transistor or logic-level MOSFET driving the heavy load. Step 4: Check for Solder Bridges