PIR motion sensor (SR501)
HC-SR501 passive infrared motion sensor · 4.5–20 V · output 3.3 V HIGH for 3 s after movement (re-triggers) · up to 7 m, 110° cone · needs about a minute to settle after power-up (shortened here)
Try it on the benchThe lab drops it on an empty bench and opens its datasheet card.
Typical part: HC-SR501 PIR module
Pins
- VCC
- OUT
- GND
Ratings and limits
| Supply | 4.5–20 V |
|---|---|
| Output | 3.3 V high |
| Hold time | 3 s (trimmer 3–300 s) |
| Range | ≈ 3–7 m |
How to use it
Sees changes in body heat moving across its lens, not presence: a person sitting still disappears after the hold time. Wait about a minute after power-up before trusting it.
Lessons and builds that use it
- Motion-activated light (build)
- 11. PIR sensor: only when someone is there (build)
- 12. 555 timer: stay on after they pass (build)
- 13. Buzzer: an alarm mode (build)
- 14. Solar: the light runs off-grid (build)