Analog electronics, Electronic components, Hobby, Magnetism, Projects, Sensors

Meet the reed switch

This post’s subject is a little known component: the reed switch. This is a magnetic sensor and will be explained how it works and what you can do with this component.

How it works and what it is made of?

The working principle is very simple. It has two conductor plates, which can be normally opened or closed, which move in the presence of a magnetic field.

These contacts open the circuit if the plates are normally closed, or close the circuit if are normally opened. The plates stay inside a glass capsule containing nitrogen gas for be inert. An inert gas don`t react with other substances in normal conditions of temperature and pressure. The plates can be made of rhodium, ruthenium or iridium on gold, copper or tungsten.

These are the reed switch representation in circuit schematics.

Also exists the reed switch with three terminals which switch with a magnetic field, called type c.

Some projects examples

What you can do with the reed switch? This is the schematics of a sensor with 555, change frequency when detects magnetic field.

This project in a printed circuit board.

If you don’t know the 555, click in this button.

555 555Click here

This circuit can be a magnetic sensor to Arduino or other circuit, with a digital pin.

Another way to activate the reed switch is get a piece of wire and wind in the component forming a coil.

In this way, it is possible to know the value of required current to move the contact in the component. This is an example of circuit which can be used to activate the reed switch by electrical current. You can vary the VDC or R1 to see when the LED is turned on.

The circuit in protoboard.


The reed switches are fragile components, it is easy to break the glass capsule. Therefore, must be handled with care.

About Pedro Ney Stroski

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