PIR Motion Sensor Symbol
Definition: The PIR Motion Sensor symbol represents a passive infrared detection module, commonly the HC-SR501 or equivalent, that detects movement within its field of view by sensing changes in infrared radiation emitted by warm bodies, with VCC (power supply), OUT (digital signal output), and GND (ground) terminals, per IEC 60947-5-2 proximity device conventions.
Also known as: passive infrared sensor, PIR sensor, motion detector, infrared motion sensor, PIR module, HC-SR501, body heat detector, infrared presence detector.
What the PIR Motion Sensor symbol means
The PIR Motion Sensor symbol denotes a compact electronic module that detects the presence and movement of people or animals within a defined detection zone (typically 5–7 m, up to 120° wide) by measuring changes in the infrared (IR) radiation pattern across its pyroelectric sensing elements. When movement is detected, the OUT pin outputs a logic HIGH signal to a microcontroller, PLC, or relay circuit.
In circuit and wiring diagrams the PIR Motion Sensor symbol appears in security, lighting automation, and energy-saving circuits. Its three terminals — VCC, OUT, and GND — indicate that it is a powered digital sensor module, distinct from a simple switch. The PIR sensor is 'passive' because it does not emit radiation; it only detects radiation from external sources (warm bodies).
How to identify the PIR Motion Sensor symbol
The PIR Motion Sensor symbol is drawn as a rectangle or rectangular module block (representing the sensor PCB) with a dome or lens graphic on one face to indicate the Fresnel lens that focuses infrared onto the pyroelectric element. Three terminals are labelled: VCC (positive supply, typically 5–12 V DC), OUT (digital output), and GND (ground). The label 'PIR', 'HC-SR501', or 'IR Motion' may appear inside or adjacent to the rectangle. Some circuit diagrams represent it with the IEC general sensor symbol (a diamond or circle) with an IR-wave annotation.
Function in a circuit
A PIR Motion Sensor module contains a pyroelectric infrared sensor element (typically dual-element differential type), a Fresnel lens, and a signal processing IC (e.g., BISS0001 or equivalent). The pyroelectric element generates a small voltage when the infrared radiation level across its two sensing elements changes, indicating a warm object moving through the field of view. The signal IC amplifies this signal, applies threshold detection and time delays, and drives the OUT pin HIGH (typically 3.3 V or 5 V logic) for a set pulse duration when motion is detected. Sensitivity and hold time are usually adjustable via on-board potentiometers.
Standards: IEC vs ANSI
| IEC 60617 | IEC 60947-5-2 governs proximity switches including photoelectric and pyroelectric types used in industrial applications. IEC 62368-1 covers audio/video, information and communications technology equipment, relevant to PIR module EMC and safety. For building automation, EN 50131 (intruder alarm systems) specifies passive infrared detector performance. |
|---|---|
| ANSI/IEEE 315 | UL 639 (intruder detection units) covers passive infrared motion detectors for security applications. UL 508 covers industrial control components including sensor modules. ANSI/NFPA 731 addresses the installation of electronic premises security systems including PIR detectors. |
| Key difference | No distinct IEC vs ANSI schematic symbol difference exists for PIR sensors; both use a generic sensor block representation. The relevant performance standards differ: EN 50131 (European/IEC) vs UL 639 (North American) for security-grade PIR detectors. The HC-SR501 module used in DIY electronics follows no specific schematic symbol standard. |
Terminals / pins
| Pin | Name |
|---|---|
| vcc | VCC |
| out | OUT |
| gnd | GND |
Typical values
Supply voltage VCC: 4.5–20 V DC (HC-SR501 module); quiescent current: 50–65 µA; output voltage HIGH: VCC − 0.5 V (logic HIGH); output current: up to 10 mA; detection range: up to 7 m (adjustable); detection angle: up to 120°; delay time: 0.3 s – 5 min (adjustable via pot); hold time (output pulse width): adjustable 0.3–5 s to minutes.
Where the PIR Motion Sensor symbol is used
- Automatic lighting control: PIR sensor output connected to a relay or TRIAC to switch lights on when someone enters a room, reducing energy consumption
- Security and intruder alarm systems: motion detection in residential and commercial burglar alarm panels, triggering sirens or alerts when motion is detected in protected zones
- Microcontroller projects: Arduino, ESP32, or Raspberry Pi circuits where the OUT pin connects to a digital input to detect human presence and trigger actions
- HVAC energy management: occupancy detection to enable/disable heating, cooling, or ventilation when a room is occupied or vacant
- IoT home automation: integrated with smart home controllers (Home Assistant, ESP-Home) to automate lighting, security cameras, and notifications
- Access control corridors: detecting approach of a person to trigger automatic door opening or access logging
Example
In an Arduino automatic night-light schematic, the PIR Motion Sensor's VCC pin connects to the Arduino 5 V rail, GND to Arduino GND, and OUT to Arduino digital pin D7. A relay module on D8 controls a 230 V AC lamp. The sketch monitors D7; when OUT goes HIGH (motion detected), the sketch activates the relay on D8 to switch on the lamp, then starts a 30-second countdown before switching the lamp off if no further motion is detected.
Key facts
- The PIR Motion Sensor symbol represents a passive infrared motion detection module with three terminals: VCC (power supply), OUT (digital logic output), and GND (ground).
- PIR sensors are 'passive' — they do not emit any radiation; they detect changes in the ambient infrared radiation pattern caused by warm moving bodies.
- The HC-SR501 is the most widely used low-cost PIR module in electronics projects, operating from 4.5–20 V DC with adjustable sensitivity and hold-time potentiometers.
- When motion is detected, the OUT pin goes logic HIGH (typically at VCC voltage) for a duration set by the on-board hold-time potentiometer; no motion returns OUT to LOW.
- Detection range is typically up to 7 m with a 120° field of view; both parameters are adjustable on most modules via on-board trimmer potentiometers.
- The PIR module contains a pyroelectric sensor element, a Fresnel lens (which focuses infrared from the detection zone onto the sensor), and a BISS0001 or equivalent signal processing IC.
- Quiescent current is very low (50–65 µA), making PIR sensors suitable for battery-powered wireless sensor applications.
- IEC EN 50131-2-2 and UL 639 define performance grades for security-grade passive infrared detectors used in professional alarm systems.
Diagrams that use this symbol
- motion sensor wiring diagram
- pir wiring diagram
- pir sensor pin diagram
- motion sensor light wiring diagram
- pir sensor diagram
- 3 wire motion sensor light wiring diagram
- pir sensor circuit diagram
- motion sensor diagram
Frequently asked questions
What does the PIR motion sensor symbol mean in a circuit diagram?
The PIR Motion Sensor symbol means that a passive infrared motion detection module is present at that point in the circuit. When a warm body (person or animal) moves within the sensor's detection zone, the OUT pin switches to logic HIGH, providing a digital signal to the connected microcontroller, PLC input, or relay driver to trigger the desired action (lights on, alarm, etc.).
What does the PIR sensor symbol look like?
The PIR Motion Sensor symbol is drawn as a rectangle (representing the module PCB) with a dome or lens graphic on the front face. Three terminals are labelled VCC (supply), OUT (signal output), and GND (ground). The label 'PIR' or 'HC-SR501' typically annotates the symbol. Some diagrams show it as a generic sensor block with an infrared wave annotation.
What are the pins on a PIR motion sensor?
A PIR Motion Sensor has three terminals: VCC (positive supply voltage, typically 5–12 V DC), OUT (digital logic output — goes HIGH when motion is detected, LOW when no motion), and GND (ground/negative supply). The OUT pin can drive a microcontroller input directly or a relay/transistor driver for higher-current loads.
What is the difference between a PIR sensor and a microwave motion sensor?
A PIR (passive infrared) sensor detects motion by sensing changes in the infrared radiation pattern from warm bodies and works best for slow-moving or large targets; it cannot detect motion through walls. A microwave motion sensor emits and detects reflected microwave radiation and can detect motion through non-metallic materials, but it is more susceptible to false triggers from air conditioning and moving objects.
What voltage and current does a PIR sensor require?
The HC-SR501 PIR module operates from 4.5–20 V DC on the VCC pin, drawing 50–65 µA in standby. The OUT pin output voltage is approximately VCC when HIGH; output current capability is up to 10 mA, sufficient to drive a microcontroller input or a small relay coil. For loads requiring more current, connect OUT to a transistor or relay driver.
What standard governs PIR motion sensor performance?
For security applications, EN 50131-2-2 (Europe/IEC) and UL 639 (North America) define performance requirements for passive infrared detectors. For industrial proximity sensing, IEC 60947-5-2 applies. The HC-SR501 DIY module typically carries CE marking (EN 55032 for EMC) but is not certified to security alarm standards.
Why does a PIR sensor output stay HIGH after motion stops?
The PIR sensor's OUT pin remains HIGH for a hold time (also called retriggering or output duration) after the last motion detection. This hold time is set by an on-board potentiometer (typically adjustable from 0.3 seconds to several minutes on HC-SR501 modules). The hold time prevents the output from rapidly toggling and allows connected devices (lights, alarms) to stay active for a usable period after someone stops moving.
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