HC-SR501 PIR Module Symbol
Definition: The HC-SR501 PIR Module symbol represents a passive infrared motion-detection module drawn as a labeled square with concentric circles indicating the sensor lens and three pins (VCC, OUT, GND), denoting a pyroelectric infrared sensor module that detects motion by sensing changes in infrared radiation emitted by warm-bodied objects in its field of view, as used in embedded systems and home-automation circuit diagrams.
Also known as: PIR sensor symbol, HC-SR501 symbol, passive infrared sensor module symbol, motion sensor module symbol, PIR module schematic symbol.
What the HC-SR501 PIR Module symbol means
Note: This symbol is keyed as 'sonar-module' in the symbol library but the actual component is the HC-SR501 PIR (Passive Infrared) Motion Detection Module — a different sensor technology from ultrasonic sonar. The symbol represents the HC-SR501 PIR module, which detects motion by measuring changes in infrared (heat) radiation patterns across a Fresnel lens array rather than by emitting and receiving ultrasonic pulses. In circuit diagrams, the symbol identifies a self-contained motion-detection block that outputs a digital HIGH signal on the OUT pin when movement is detected, requiring only a 5 V supply and ground connection.
The three-pin interface — VCC (power), OUT (digital output), and GND (ground) — makes the PIR module symbol one of the simplest sensors in a schematic to connect to a microcontroller. The symbol is used in home security systems, automatic lighting control, occupancy detection, energy management, and alarm circuits wherever passive motion sensing is required. The concentric circles in the symbol represent the multi-zone Fresnel lens that focuses incident infrared radiation onto the pyroelectric sensing element.
How to identify the HC-SR501 PIR Module symbol
The HC-SR501 PIR Module symbol is a square with two concentric circles centered inside the box, labeled 'PIR' at the center, representing the dome-shaped Fresnel lens of the module. Three pin stubs exit from the left edge: the top pin is VCC (power supply), the middle pin is OUT (digital output), and the bottom pin is GND (ground). The concentric-circles motif and 'PIR' label clearly distinguish this from an ultrasonic sensor module (which shows two transducer circles side by side with 'TRIG' and 'ECHO' pins) and from a photoelectric sensor (single circle without the 'PIR' label).
Function in a circuit
The HC-SR501 PIR module detects motion by monitoring changes in the total infrared radiation incident on a dual-element pyroelectric sensor behind a Fresnel lens. When a warm body (human or animal) moves through the sensor's field of view (typically 120° cone, 3–7 m range), the differential infrared pattern across the two sensing elements generates a voltage signal, which is amplified and processed by an internal comparator (typically a BISS0001 IC). The OUT pin goes HIGH (typically 3.3 V output on a 5 V supply) for an adjustable hold time (0.3–5 minutes via onboard potentiometer) and returns LOW after no motion is detected. Sensitivity range and delay time are set by two onboard trimpots.
Standards: IEC vs ANSI
| IEC 60617 | No specific IEC 60617 symbol is defined for PIR sensor modules. IEC 61496 governs electrosensitive protective equipment (light curtains and presence sensing), but PIR modules used in consumer and embedded applications are not covered by a specific IEC graphical symbol standard. The labeled rectangle/square with concentric circles is an application-defined convention. |
|---|---|
| ANSI/IEEE 315 | ANSI Y32.2/IEEE 315 does not define a specific symbol for PIR sensor modules. In US P&ID and instrumentation practice (ISA 5.1), a presence sensor would be tagged as 'SQ' (speed/presence detector) or 'PS', but a specific glyph for the HC-SR501 module does not exist in ANSI standards. |
| Key difference | No standard-defined glyph difference exists between IEC and ANSI for this module. Both conventions use a labeled block symbol. The symbol appearance on circuit diagram tools is manufacturer/tool-defined rather than standards-mandated. |
Terminals / pins
| Pin | Name |
|---|---|
| vcc | VCC |
| out | OUT |
| gnd | GND |
Typical values
Supply voltage (VCC): 4.5–20 V DC (typically 5 V). Quiescent current: less than 60 µA. Output voltage (HIGH): approximately 3.3 V. Detection range: up to 7 m (adjustable 3–7 m). Detection angle: approximately 120° horizontal. Hold time: 0.3 s to 5 min (adjustable via onboard potentiometer). Trigger mode: single or repeating (selectable by jumper). Operating temperature: −20°C to +80°C.
Where the HC-SR501 PIR Module symbol is used
- Home security alarm systems triggering a buzzer or notification when motion is detected in a room
- Automatic corridor lighting controllers switching LED or fluorescent lights on when occupancy is detected
- Arduino and Raspberry Pi hobbyist projects for motion-activated cameras, data loggers, and doorbell systems
- Energy-saving systems in commercial buildings turning off HVAC or lighting in unoccupied zones
- Wildlife monitoring and camera trap circuits activated by animal movement in outdoor environments
- Intruder detection perimeter systems in warehouses or retail locations wired to central alarm panels
Example
In an Arduino-based automatic night light circuit, the HC-SR501 PIR module symbol shows VCC connected to the 5 V pin of the Arduino, GND to ground, and OUT to digital pin D2. When the module detects a person entering the room, OUT goes HIGH for the hold time (set to 30 seconds by the onboard potentiometer), triggering an interrupt service routine that switches on a relay-controlled LED strip. The PIR module consumes less than 60 µA in standby, making the circuit suitable for battery operation.
Key facts
- The HC-SR501 PIR Module symbol represents a passive infrared motion sensor module with three pins: VCC (4.5–20 V supply), OUT (digital output HIGH on motion detection), and GND (ground).
- The symbol uses concentric circles inside a square to represent the Fresnel lens dome of the module; the label 'PIR' identifies it as a passive infrared — not ultrasonic — sensor.
- The HC-SR501 detects infrared (heat) radiation changes from warm bodies; it is a passive sensor that does not emit any radiation, unlike ultrasonic sensors that emit and receive sound pulses.
- Detection range is typically up to 7 m with a 120° field of view, adjustable via onboard sensitivity potentiometer.
- The OUT pin outputs approximately 3.3 V (HIGH) when motion is detected and 0 V (LOW) when no motion is present, making it directly compatible with 3.3 V and 5 V microcontroller GPIO pins.
- Quiescent current consumption is less than 60 µA, making the HC-SR501 suitable for battery-powered and low-power IoT applications.
- Hold time (the duration OUT remains HIGH after last motion detection) is adjustable from approximately 0.3 seconds to 5 minutes via a trimpot on the module.
- Note: Despite the symbol's 'sonar-module' key in this library, the represented component is the HC-SR501 PIR passive infrared module, not an ultrasonic sonar sensor. For an ultrasonic distance sensor, see the 'ultrasonic' symbol.
Frequently asked questions
What does the PIR sensor module symbol look like in a circuit diagram?
The HC-SR501 PIR Module symbol is a square with two concentric circles in the center labeled 'PIR', representing the Fresnel lens dome. Three pin stubs extend from the left side: VCC (top, power supply), OUT (middle, digital output), and GND (bottom, ground). This distinguishes it from an ultrasonic module (two side-by-side transducer circles) and from simple photodiode sensors.
What does the PIR sensor module do in a circuit?
The HC-SR501 PIR module detects motion by sensing changes in infrared (heat) radiation emitted by warm bodies moving through its 120° field of view (up to 7 m range). When motion is detected, the OUT pin goes HIGH (approximately 3.3 V) for an adjustable hold time, providing a digital signal that a microcontroller or relay circuit can use to trigger alarms, lights, or other actions.
What is the difference between a PIR sensor and an ultrasonic sensor symbol?
A PIR sensor symbol shows concentric circles (the lens) with 3 pins (VCC, OUT, GND), representing a passive infrared motion detector that senses heat radiation. An ultrasonic sensor symbol shows two side-by-side transducer circles with 4 pins (VCC, TRIG, ECHO, GND), representing an active distance-measuring device that emits and times the return of ultrasonic sound pulses. PIR sensors detect motion; ultrasonic sensors measure distance.
How do you connect the HC-SR501 PIR module to an Arduino?
Connect the VCC pin to the Arduino's 5 V output, the GND pin to Arduino GND, and the OUT pin to any digital input pin (e.g., D2). No pull-up or pull-down resistor is required — the module includes internal signal conditioning. The OUT pin goes HIGH for the programmed hold time when motion is detected and returns LOW otherwise.
What voltage does the HC-SR501 PIR module operate at?
The HC-SR501 PIR module operates from 4.5 V to 20 V DC on the VCC pin, with 5 V being the most common supply. The output signal is approximately 3.3 V HIGH regardless of supply voltage, making it compatible with both 3.3 V (Raspberry Pi) and 5 V (Arduino) microcontrollers without a level shifter.
What is the detection range and angle of the HC-SR501?
The HC-SR501 PIR module has an adjustable detection range of approximately 3–7 m, set by the sensitivity trimpot. The horizontal detection angle is approximately 120°. The sensor is most sensitive to motion across the field of view (lateral movement) rather than toward it (radial movement) due to the pyroelectric detection principle.
What standard governs the PIR sensor module symbol?
No IEC 60617 or ANSI Y32.2/IEEE 315 standard defines a specific graphical symbol for PIR sensor modules. The labeled square with concentric circles is a tool-defined convention used in embedded-system and hobbyist schematics. In industrial P&ID practice per ISA 5.1, a presence detector would be tagged with an instrument bubble rather than a module outline.
Place the HC-SR501 PIR Module symbol on a wiring diagram or schematic in the free online circuit diagram maker — no download required.