A PIR sensor (Passive Infrared sensor) detects motion by sensing changes in infrared (heat) radiation from objects, people, or animals in its field of view, making them ideal for security alarms, automatic lighting and smart home systems. The HC-SR501 is a popular, passive infrared (PIR) motion sensor module designed to detect human or animal movement within a 3–7 meter range, commonly used in security and automation systems. They are “passive” because they don’t emit energy but instead measure the infrared light naturally emitted by warm bodies, triggering a signal when a temperature difference indicates movement.
Working Voltage Range: DC 4.5V- 20V
Current Drain: <60uA
Detection Range: <140°
Voltage Output: High/Low level Signal: 3.3V TTL output
Detection Distance: 3 to 7m (can be adjusted)
Delay Time: 5 to 200s (Can be Adjusted, Default 5s)
Output goes high when objects enter the sensing range, and automatically returns to low when object leaves
Sensitivity Adjustment: A potentiometer on the board allows you to adjust the sensing distance from approximately 3 meters to 7 meters. Turning the potentiometer clockwise increases the range.
Time Delay Adjustment: Another potentiometer controls how long the output signal stays high after motion is detected. This delay is adjustable, typically from 5 seconds up to 300 seconds (5 minutes)
Trigger Mode Selection: A jumper cap allows selection between two modes:
“H” (Repeatable Trigger): If motion is detected again during the delay time, the delay counter is reset and the output remains high.
“L” (Non-repeatable/Single Trigger): The output goes high upon initial detection and stays high for the set delay time, after which it goes low regardless of continued motion.
Usage Tips
Initialization: The sensor requires a 1-minute warmup; it may produce false positives during this time.
Placement: Avoid pointing directly at windows, moving objects, or heat sources.
