What does it do?
The Hall effect sensor produces an output signal that changes when a magnet is near.
How does it operate?
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Hall effect sensor circuit
There is no symbol for a Hall effect
sensor in Livewire or Circuit Wizard.
The sensor’s action can be simulated with a potential divider. |
The Hall effect sensor senses the ‘magnetic field’ (the field near a magnet or around a wire carrying a current).
These notes apply to the Allegro A1301 (Rapid order code 82-1020) Hall effect sensor.
The supply voltage needs to be in the range 4.5 to 6.0V.
The output signal voltage from the sensor changes in proportion to the magnetic field.
If there is no magnetic field, the output signal voltage is equal to half the supply voltage. |
If a south magnetic pole (or face) of a magnet is brought next to the front face of the sensor the output signal voltage increases. A north magnetic pole (or face) decreases the output signal voltage.
The rate of change of the output signal voltage with magnetic field is typically 2.5 V per tesla
If the signal from the Hall effect sensor is to be used with a digital system then the analogue signal from the sensor needs to be fed to a comparator.
Possible applications
- Sensing the closeness of a magnet, or any object wit an attached magnet
- Measuring the strength of a magnetic field
Making
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Pins of Hall effect sensor |
How part of the PCB might look
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Testing
Make sure that the signal going out (on the green PCB track) changes from half of the value of +Vs (the supply voltage) when a magnet is brought near.
Fault finding
If there is a fault, check that:
- The voltage on the centre pin is low (0V)
- The voltage on the left-hand pin in the above pin diagram is high (the supply voltage)
If there is a fault, check the tracks and solder joints.
Alternatives
- A reed switch/proximity switch can also detect the presence of a magnet. The Hall effect sensor has the advantages of being more robust and not producing switch bounce. A Hall effect sensor is more expensive than a reed switch.
- A microswitch or a light sensor can be used to detect if an object is near.
- Optoswitches are useful for detecting when an object is near to the sensor, but they are more expensive.
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