Adafruit
Mini Basic PIR Sensor - BL412
The BL412 is a compact passive infrared (PIR) motion sensor designed for detecting movement from people and animals at distances of approximately 3–8 m. Much...
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The BL412 is a compact passive infrared (PIR) motion sensor designed for detecting movement from people and animals at distances of approximately 3–8 m. Much smaller than standard PIR modules, it is well suited for unobtrusive projects and fits easily on breadboards or perfboard.
The sensor runs on 3.3 V and requires only power, ground, and an optional resistor divider to set the output hold time — from 2 seconds (pin 2 tied to ground) up to one hour (pin 2 at 3.3 V). The digital signal output is 3.3 V high/low. The snap-on lens provides a 120° detection spread focused at approximately 5 m.
Key Features
- Compact Size – Smaller than standard PIR modules for discreet installations
- 3.3 V Operation – Low-voltage, breadboard-friendly
- Adjustable Hold Time – 2 seconds to 1 hour via resistor divider on pin 2
- 120° Detection Angle – Wide field of view with snap-on lens
- Simple Wiring – Only 4 pins: GND, on-time, VCC, signal
Wiring
- Pin 1 – Ground
- Pin 2 – On-time control (ground for 2 s; resistor divider for longer delays)
- Pin 3 – 3.3 V power
- Pin 4 – Digital signal output (3.3 V high when motion detected)
Specifications
- Model – BL412
- Supply Voltage – 3.3 V
- Detection Range – Approximately 3–8 m (optimised at 5 m)
- Detection Angle – 120°
- Output – Digital, 3.3 V high/low
- Hold Time – 2 s to 1 hour (adjustable)
- Sensor Window – 5 × 3.8 mm
Ideal For
- Motion-activated lighting and alarms
- Occupancy detection projects
- Low-power battery-operated sensors
- Arduino and Raspberry Pi motion sensing
Package Contents
- 1× BL412 Mini PIR sensor with snap-on lens
Resources
Jargon buster
Plain-language definitions for the technical terms used above.
- GND
- GND is the ground or reference connection (0 V) for a circuit. When connecting two devices together, their grounds must be joined so both agree on what counts as a low or high signal.
- microcontroller
- A microcontroller is a small computer on a single chip that runs a stored program and controls connected inputs and outputs such as buttons, sensors, displays and communication interfaces. In a device built around one, it is the part that executes the code and coordinates the device's behaviour.
- PIR sensor
- A passive infrared sensor detects changes in heat, usually from a person moving across its view. It matters because PIR sensors are common for lights and alarms, but they can miss people who are present but not moving much.
- VCC
- VCC is the positive power-supply connection on a chip or module. Connecting it to the correct supply voltage is needed for the part to power on and helps avoid damaging the electronics.
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pir passive infrared proximity motion sensor
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