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.. _2.2.4_c_pi5:

2.2.4 Reed Switch Module
==============================

Introduction
-------------------

In this project, we will learn about the reed switch, which is an electrical switch that operates by means of an applied magnetic field.

.. image:: ../img/2.2.4reed_switch.png
    :width: 300
    :align: center

Required Components
------------------------------

In this project, we need the following components. 

.. image:: ../img/2.2.4component.png
    :width: 700
    :align: center

It's definitely convenient to buy a whole kit, here's the link: 

.. list-table::
    :widths: 20 20 20
    :header-rows: 1

    *   - Name	
        - ITEMS IN THIS KIT
        - LINK
    *   - Raphael Kit
        - 337
        - |link_Raphael_kit|

You can also buy them separately from the links below.

.. list-table::
    :widths: 30 20
    :header-rows: 1

    *   - COMPONENT INTRODUCTION
        - PURCHASE LINK

    *   - :ref:`cpn_gpio_extension_board`
        - |link_gpio_board_buy|
    *   - :ref:`cpn_breadboard`
        - |link_breadboard_buy|
    *   - :ref:`cpn_wires`
        - |link_wires_buy|
    *   - :ref:`cpn_resistor`
        - |link_resistor_buy|
    *   - :ref:`cpn_led`
        - |link_led_buy|
    *   - :ref:`cpn_reed_switch`
        - |link_reed_switch_buy|

Schematic Diagram
-----------------------

============ ======== ======== ===
T-Board Name physical wiringPi BCM
GPIO17       Pin 11   0        17
GPIO27       Pin 13   2        27
GPIO22       Pin 15   3        22
============ ======== ======== ===

.. image:: ../img/reed_schematic.png
    :width: 400
    :align: center

.. image:: ../img/reed_schematic2.png
    :width: 400
    :align: center

Experimental Procedures
-------------------------------

**Step 1:** Build the circuit.

.. image:: ../img/2.2.4fritzing.png
    :width: 700
    :align: center

**Step 2:** Change directory.

.. raw:: html

   <run></run>

.. code-block::

    cd ~/raphael-kit/c/2.2.4/

**Step 3:** Compile.

.. raw:: html

   <run></run>

.. code-block::

    gcc 2.2.4_ReedSwitch.c -lwiringPi

**Step 4:** Run.

.. raw:: html

   <run></run>

.. code-block::

    sudo ./a.out

The green LED will light up when the code is run. If a magnet is placed close to the reed switch module, the red LED lights up; take away the magnet and the green LED lights up again.

.. note::

    If it does not work after running, or there is an error prompt: \"wiringPi.h: No such file or directory\", please refer to :ref:`install_wiringpi`.

**Code**

.. code-block:: c

    #include <wiringPi.h>
    #include <stdio.h>

    #define ReedPin		0
    #define Gpin		2
    #define Rpin		3

    void LED(char* color)
    {
        pinMode(Gpin, OUTPUT);
        pinMode(Rpin, OUTPUT);
        if (color == "RED")
        {
            digitalWrite(Rpin, HIGH);
            digitalWrite(Gpin, LOW);
        }
        else if (color == "GREEN")
        {
            digitalWrite(Rpin, LOW);
            digitalWrite(Gpin, HIGH);
        }
        else
            printf("LED Error");
    }

    int main(void)
    {
        if(wiringPiSetup() == -1){ //when initialize wiring failed,print messageto screen
            printf("setup wiringPi failed !");
            return 1; 
        }

        pinMode(ReedPin, INPUT);
        LED("GREEN");
        
        while(1){
            if(0 == digitalRead(ReedPin)){
                delay(10);
                if(0 == digitalRead(ReedPin)){
                    LED("RED");	
                    printf("Detected Magnetic Material!\n");	
                }
            }
            else if(1 == digitalRead(ReedPin)){
                delay(10);
                if(1 == digitalRead(ReedPin)){
                    while(!digitalRead(ReedPin));
                    LED("GREEN");
                }
            }
        }
        return 0;
    }

**Code Explanation**

.. code-block:: c

    #define ReedPin		0
    #define Gpin		2
    #define Rpin		3

Pin GPIO17, GPIO27 and GPIO22 of the T_Extension Board is corresponding to 
the GPIO0, GPIO2 and GPIO3 in wiringPi. Assign GPIO0, GPIO2 and GPIO3 to 
``ReedPin``, ``Gpin`` and ``Rpin``.

.. code-block:: c

    void LED(char* color)
    {
        pinMode(Gpin, OUTPUT);
        pinMode(Rpin, OUTPUT);
        if (color == "RED")
        {
            digitalWrite(Rpin, HIGH);
            digitalWrite(Gpin, LOW);
        }
        else if (color == "GREEN")
        {
            digitalWrite(Rpin, LOW);
            digitalWrite(Gpin, HIGH);
        }
        else
            printf("LED Error");
    }

Set a ``LED()`` function to control the 2 LEDs, the parameter of this function is ``color``.

When ``color`` is ``"RED"``, set ``Rpin`` to ``HIGH`` (light up the red LED) and ``Gpin`` to ``LOW`` (turn off the green LED); when ``color`` is ``"GREEN"``, then light up the green LED and turn off the red LED. 

.. code-block:: c

    while(1){
            if(0 == digitalRead(ReedPin)){
                delay(10);
                if(0 == digitalRead(ReedPin)){
                    LED("RED");	
                    printf("Detected Magnetic Material!\n");	
                }
            }
            else if(1 == digitalRead(ReedPin)){
                delay(10);
                if(1 == digitalRead(ReedPin)){
                    while(!digitalRead(ReedPin));
                    LED("GREEN");
                }
            }
        }

Read the value of the reed switch module, if the value read 2 times is 0, call ``LED("RED")`` to light up the red LED and print ``"Magnetic material detected!"``.

If the value is 1, the green LED is lit.


Phenomenon Picture
------------------------

.. image:: ../img/2.2.4reed_switch.JPG
    :width: 500
    :align: center