Lesson 11 Reed Switch

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Introduction

A reed switch (as shown below) is used to detect the magnetic field. Hall sensors are generally used to measure the speed of intelligent vehicles and count in assembly lines, while reed switches are often used to detect the existence of a magnetic field.

Required Components

– 1 * Raspberry Pi

 1 * Breadboard

– 1 * Reed switch module

– 1 * Dual-color LED module

– 2 * 3-Pin anti-reverse cable

– 1 * Magnet (Self provided)

Experimental Principle

A reed switch is a type of line switch component that realizes control by magnetic signals. It induces by a magnet. The “switch” here means dry reed pipe, which is a kind of contact passive electronic switch component with the advantage of simple structure, small size, and convenient control. The shell of a reed switch is commonly a sealed glass pipe in which two iron elastic reed electroplates are equipped and inert gases are filled. Normally, the two reeds made of special materials in the glass tube are separated. However, when a magnetic substance approaches the glass tube, the two reeds in the glass tube are magnetized to attract each other and contact under the function of magnetic field lines. As a result, the two reeds will pull together to connect the circuit connected with the nodes.

After external magnetic force disappears, the two reeds will be separated with each other because they have the same magnetism, so the circuit is also disconnected. Therefore, as a line switch component controlling by magnetic signals, the dry reed pipe can be used as a sensor to count, limit positions and so on. At the same time, it is widely used in a variety of communication devices. 

The schematic diagram of the module is as shown below:

Experimental Procedures

Step 1: Build the circuit

Raspberry PiGPIO Extension BoardReed Switch Module
GPIO0GPIO17SIG
3.3V3V3VCC
GNDGNDGND
Raspberry PiGPIO Extension BoardDual-color LED Module
GPIO1GPIO18R
GNDGNDGND
GPIO2GPIO27G

For C Users:

Step 2: Change directory. 

    cd /home/pi/SunFounder_SensorKit_for_RPi2/C/11_reed_switch/

Step 3: Compile.

    gcc reed_switch.c -lwiringPi

Step 4: Run.

    sudo ./a.out

For Python Users:

Step 2: Change directory. 

    cd /home/pi/SunFounder_SensorKit_for_RPi2/Python/

Step 3: Run.

    sudo python3 11_reed_switch.py

Then the LED will flash green. Place a magnet near the reed switch, “Detected Magnetic Material!” will be printed on the screen and the LED will change to red. Move away the magnet, the LED will turn green again.