Hall Effect Sensor Symbol
Definition: The Hall Effect Sensor symbol represents a three-terminal semiconductor transducer — with VCC (supply), GND, and OUT pins — that produces a voltage output proportional to, or a digital switching signal triggered by, the presence of a magnetic field perpendicular to the current-carrying sensing element, based on the Hall effect discovered by Edwin Hall in 1879 and standardised in sensor interface descriptions per IEC 60947-5-6 and manufacturer application notes.
Also known as: Hall effect sensor, Hall sensor, Hall probe, magnetic sensor, Hall switch, linear Hall sensor, Hall IC.
What the Hall Effect Sensor symbol means
The Hall Effect Sensor symbol denotes a solid-state magnetic sensor that exploits the Hall effect: when a current-carrying conductor is placed in a magnetic field perpendicular to the current, a voltage (the Hall voltage) develops across the conductor transverse to both current and field. In integrated Hall sensor ICs, this physics is converted to a usable output — either a linear voltage proportional to field strength (linear Hall sensor) or a digital logic level that switches when the field exceeds a threshold (digital Hall switch).
In schematics the Hall Effect Sensor symbol is a rectangular block labelled 'HALL SENSOR' with three pins: VCC (supply voltage, typically 3.3 V or 5 V), GND (power return), and OUT (the sensor output — analog or digital). The output pin drives directly into ADC inputs (linear type) or MCU digital inputs (digital type). A pull-up resistor is often shown on the OUT line when an open-collector output type (such as the A3144) is used.
How to identify the Hall Effect Sensor symbol
The Hall Effect Sensor symbol is drawn as a rectangular block labelled 'HALL SENSOR' or 'HALL EFFECT SENSOR'. The VCC pin (supply) is at the upper left, GND at the lower left, and OUT (output) at the right. In some representations the block contains a small 'H' symbol or a bar magnet icon to indicate the magnetic sensing function. Physical Hall sensor ICs (e.g., A1302, SS49E, A3144) are typically three-pin TO-92 or SOT-23 packages; in schematics these are often drawn as a three-terminal IC block.
Function in a circuit
A Hall effect sensor measures the presence, polarity, and magnitude of a magnetic field. When a magnetic field with sufficient flux density (measured in millitesla, mT, or gauss, G) is applied perpendicular to the sensor face, the Hall voltage is generated. In a digital Hall switch (e.g., A3144) the output transistor switches LOW when the field exceeds the operate point B_OP (e.g., −40 gauss for south pole) and returns HIGH when it drops below the release point B_RP (hysteresis prevents chatter). In a linear Hall sensor (e.g., A1302) the output voltage varies linearly with field strength — typically 1.3 mV/gauss — centred at VCC/2 for zero field. The open-collector output of digital Hall switches requires an external pull-up resistor (typically 10 kΩ) to VCC.
Standards: IEC vs ANSI
| IEC 60617 | IEC 60947-5-6 (Low-voltage switchgear — DC interface for proximity sensors and switching amplifiers with defined interface) addresses proximity sensor output interface standards, applicable to Hall-effect proximity switches. IEC 60617 does not define a unique symbol for a Hall sensor; it is represented as a labelled sensor block per general IEC block conventions. |
|---|---|
| ANSI/IEEE 315 | IEEE 315-1975 (ANSI Y32.2) does not define a specific symbol for a Hall effect sensor. In North American schematics it is drawn as a three-terminal sensor block labelled 'HALL' or 'HALL EFFECT SENSOR', with VCC, GND, and OUT annotations per general IEEE 315 transducer block conventions. |
| Key difference | Both IEC and IEEE/ANSI use a labelled rectangular block for the Hall sensor. The IEC three-wire DC PNP/NPN interface (IEC 60947-5-6) is used in industrial proximity sensor Hall switches; North American practice uses the same three-terminal pinout. The key difference in practice is the output logic: European industrial Hall switches commonly use PNP (source) output; North American and electronics applications commonly use NPN (sink) open-collector output. |
Terminals / pins
| Pin | Name |
|---|---|
| vcc | VCC |
| gnd | GND |
| out | OUT |
Typical values
Supply voltage VCC: 3 V to 24 V (type-dependent; 3.3 V or 5 V for electronics, up to 24 V for industrial types). Supply current: 4–12 mA quiescent. Output voltage (linear, A1302): 2.5 V at 0 G, sensitivity 1.3 mV/G. Operate point (digital, A3144): −40 G to −95 G (south pole). Release point (A3144): −25 G to −80 G. Output type: open collector (NPN) requiring 10 kΩ pull-up to VCC. Magnetic flux density range: ±1000 G (linear), up to ±2000 G (for encoder types).
Where the Hall Effect Sensor symbol is used
- Brushless DC (BLDC) motor commutation — three Hall sensors detect rotor magnet position to control three-phase PWM commutation in power tools, drones, and EV drives
- Speed and position sensing in encoders — a Hall sensor detects the teeth of a ferromagnetic gear or the poles of a magnetic ring encoder for tachometer and odometer applications
- Proximity detection — Hall switches in door, lid, and position sensors detect permanent magnet actuators for tamper detection, lid-open sensing, and end-stop detection in printers and appliances
- Current sensing — Hall-effect current transducers (e.g., ACS712) measure AC and DC currents non-contactly by sensing the magnetic field around a current-carrying conductor
- Angular position sensing in potentiometer-free joysticks and throttle controls — linear Hall sensors measure the angle of a rotating magnet for contactless, wear-free position feedback
- Anti-lock braking system (ABS) wheel speed sensors — Hall sensors in automotive ABS detect wheel rotation speed from a toothed ring gear on the axle
- Magnetic levitation and linear motor control — Hall sensors provide real-time position feedback for active magnetic suspension and linear drive positioning
Example
In a BLDC motor control schematic for a drone ESC (electronic speed controller), three Hall Effect Sensor symbols are shown mounted 120° apart inside the motor stator. Each sensor's VCC pin connects to the 5 V supply rail, GND to the common ground, and OUT to a microcontroller digital input (MCU pins D2, D3, D4 with internal pull-ups enabled). The MCU reads the three Hall signals as a 3-bit Gray code that changes with each 60° of rotor rotation, using the sequence to determine rotor position and fire the correct stator winding phase via the gate driver.
Key facts
- The Hall Effect Sensor is a three-terminal magnetic transducer that measures the presence and strength of a magnetic field via the Hall effect (discovered 1879); in circuit diagrams it has three pins: VCC (supply), GND, and OUT (signal output), per sensor manufacturer application standards.
- Digital Hall switches (e.g., A3144, OH090U) produce a logic LOW output when a magnetic field exceeds the operate threshold (B_OP) and return HIGH when the field falls below the release threshold (B_RP), providing hysteresis to prevent output chatter.
- Linear Hall sensors (e.g., A1302, SS495A) produce an analog output voltage proportional to magnetic flux density — typically centred at VCC/2 for zero field, with a sensitivity of 1.3 mV/G — suitable for measuring current, angle, or field strength.
- Open-collector NPN output Hall switches (most common in electronics) require an external pull-up resistor (typically 4.7 kΩ to 10 kΩ) from the OUT pin to VCC; without it, the output floats HIGH and the sensor appears non-functional.
- BLDC motor commutation uses three Hall sensors spaced 120° apart to generate a 3-bit rotor position code that changes every 60°, providing six distinct commutation states for six-step motor control.
- Hall-effect current sensors (e.g., ACS712) integrate a Hall sensor and signal conditioning to measure AC and DC currents up to 30 A non-contactly, with output sensitivity of 66–185 mV/A, from a 5 V supply.
- The Hall voltage V_H = (I × B) / (n × q × t), where I is the bias current, B is the flux density, n is the carrier density, q is electron charge, and t is the conductor thickness — this relationship defines Hall sensor sensitivity.
Diagrams that use this symbol
- 3 wire crank sensor wiring diagram
- 3 wire speed sensor wiring diagram
- mass air flow sensor diagram
- speed sensor wiring diagram
- 3 wire cam sensor wiring diagram
- 5 wire maf sensor wiring diagram
- crank sensor wiring diagram
- bldc motor controller circuit diagram
Frequently asked questions
What does the Hall effect sensor symbol look like?
The Hall Effect Sensor symbol is a rectangular block labelled 'HALL SENSOR' or 'HALL EFFECT SENSOR' with three pins: VCC (power supply, upper left), GND (ground, lower left), and OUT (signal output, right). It may include a small magnet or 'H' icon inside to indicate magnetic sensing. Physical Hall sensors are typically 3-pin TO-92 or SOT-23 packages in circuit-level schematics.
What does a Hall effect sensor do?
A Hall effect sensor detects magnetic fields. Digital Hall sensors output a logic HIGH or LOW depending on whether a magnetic field exceeds a threshold, used for proximity detection, speed sensing, and motor commutation. Linear Hall sensors output an analog voltage proportional to field strength, used for current measurement, angular position sensing, and non-contact potentiometer replacement.
What are the pins on a Hall effect sensor?
A Hall effect sensor has three pins: VCC (supply voltage, typically 3.3 V or 5 V), GND (ground return), and OUT (the output — digital switching signal or analog voltage proportional to field strength). For digital (open-collector) Hall switches, a 4.7 kΩ to 10 kΩ pull-up resistor from OUT to VCC is required.
What is the difference between a digital Hall sensor and a linear Hall sensor?
A digital Hall sensor (Hall switch, e.g., A3144) produces a binary output: LOW when the magnetic field exceeds the operate point B_OP, HIGH otherwise. It includes hysteresis to prevent chatter. A linear Hall sensor (e.g., A1302, SS495A) produces an analog output voltage proportional to the magnetic flux density, centred at VCC/2 (e.g., 2.5 V at 5 V supply) for zero field, with a sensitivity typically of 1–13 mV/G.
Why does my Hall sensor output stay HIGH when a magnet is near?
Most digital Hall sensors (e.g., A3144) have an open-collector NPN output that requires an external pull-up resistor (4.7 kΩ to 10 kΩ) from OUT to VCC. Without the pull-up, the output pin floats HIGH regardless of magnet presence. Also verify the correct pole of the magnet is presented: most digital Hall switches (unipolar) activate only with the south pole (positive field) facing the sensor face.
What standard governs Hall effect sensors?
IEC 60947-5-6 defines the DC interface for proximity sensors (including Hall-effect proximity switches) used in industrial applications. Individual Hall sensor ICs are specified by manufacturer datasheets (e.g., Allegro Microsystems A3144, ACS712) rather than a universal IEC or IEEE standard. The three-terminal pinout and logic interface are consistent across industry practice.
Where are Hall effect sensors used in motors?
Hall effect sensors are used in brushless DC (BLDC) motors for rotor position sensing and commutation control. Three Hall sensors are placed 120° apart in the stator, each detecting the rotor's permanent magnets. The three-sensor output forms a 3-bit rotor position code that changes every 60° of rotation, providing six commutation states that the motor controller uses to sequence the three-phase stator windings for continuous rotation.
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