PIR Motion Sensor (HC-SR501)
Detects moving warm bodies and pulses its output HIGH when it sees motion.
How it works
A PIR (passive infrared) sensor watches for changes in the infrared heat radiated by people and animals. When something warm moves across its view, the digital OUT pin goes HIGH for a set time, then back LOW.
The common HC-SR501 module has two orange trimmer pots — one for sensitivity (range) and one for how long OUT stays HIGH after motion — plus a jumper to choose single-trigger or repeat-trigger mode. Read OUT with a plain digital input.
Pins
- VCC
- To 5V.
- OUT
- To a digital pin — HIGH on motion.
- GND
- To GND.
Ratings
- Voltage
- 4.5–20 V (5 V typical)
- Output
- 3.3 V HIGH on motion
- Range
- ~3–7 m, adjustable
Tips
- Give it 30–60 seconds to settle after power-up before trusting readings.
- Tune the two pots: one sets range, the other how long OUT stays HIGH.