What does it do?
| The reed switch is used to detect the presence of a magnet. |
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How does it operate?
The contacts of the reed switch are normally open, but close when a magnet is brought near.
In the usual circuit its output signal goes high when a magnet is brought near. The inverted circuit gives a low voltage when a magnet is near.
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Normal circuit |
Inverted circuit |
The reed switch circuit uses a reed switch which is normally open but is closed when a magnet comes near.
In glass-cased reed switches the contacts can be seen moving when a magnet is near.
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| Click on the circuit diagram to download a Livewire file of the circuit that you can investigate and add to your own circuit. |
The reed switch component is part of a potential divider whose output voltage is determined by the upper and lower parts of the circuit. |
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A PCB-mounting terminal block
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The reed switch is connected to the PCB by wires connected to a terminal block mounted on the PCB. |
Possible applications
- Checking if something (with a magnet attached) is near
- Counting on rotating systems
- Checking when a door or window is opened
Making
How part of the PCB might look
Testing
Make sure that the signal going out (on the green PCB track) changes from low to high when a magnet is brought near to the reed switch (or the opposite way round for the inverted circuit).
Fault finding
If there is a fault, check that:
- The resistance of the reed switch component changes from a high resistance to a low resistance when a magnet is brought near.
If there is a fault, check the tracks and solder joints.
Alternatives
Web links
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