PIR - Passive Infrared Sensor

PIR - Passive Infrared Sensor



  • Human or animals will emit heat (as infrared radiation)
  • Senses infrared waves to detect motion
  • Uses
    • Alarms
    • Motion sensing cameras / lights
  • Not a distance sensor

PIR Specifications

  • Distance range: up to 20 feet
  • Detection range: ~110 degrees x 70 degrees
  • Specifications vary by device and lens


  • Main sensor is the small metal disc which detection infrared radiation https://cdn.sparkfun.com//assets/parts/1/0/5/3/5/13285-04.jpg

## Components

  • Clear / white lenses acts to focus a wider area of radiation onto the sensor to increase range


Operation (Sparkfun PIR)

  • Requires 1-2 sec delay in setup() to get initial reading from room
  • Digital output from AL pin
  • HIGH when no movement detected
  • LOW when movement detected
  • Signal remains active low for about 3 sec after movement (documentation says 15 sec but that doesn’t seem accurate)

Other Common Parameters

  • Other PIR sensors have different configurable options
    • Sensitivity (potentiometer): how much motion triggers alarm
    • Time adjust (potentiometer): how long after motion stops does signal remain active
    • Retriggering (switch / jumper): controls if alarm stays active for the same movement


PIR (Sparkfun) Argon
+ (red wire) 5v
- (white wire) GND
AL (black wire) digital input pin
(with 10K pullup resistor to 5v)

Note: The wire color and pin order is specific to the Sparkfun PIR sensor and not all PIR sensor



  • Part 1: Connect sensor; turn on on-board LED when motion is detected and turn off when motion stops
  • Part 2: Create a “hold length” of 5 sec whenever movement is detected