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.. _2.2.4_py:

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/python/

**Step 3:** Run.

.. raw:: html

   <run></run>

.. code-block::

    sudo python3 2.2.4_ReedSwitch.py

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.

**Code**

.. note::

    You can **Modify/Reset/Copy/Run/Stop** the code below. But before that, you need to go to  source code path like ``raphael-kit/python``. After modifying the code, you can run it directly to see the effect.


.. raw:: html

    <run></run>

.. code-block:: python

    #!/usr/bin/env python3
    import RPi.GPIO as GPIO
    import time

    ReedPin = 17
    Gpin    = 27
    Rpin    = 22

    def setup():
        GPIO.setmode(GPIO.BCM)       # 
        GPIO.setup(Gpin, GPIO.OUT)     # Set Green Led Pin mode to output
        GPIO.setup(Rpin, GPIO.OUT)     # Set Red Led Pin mode to output
        GPIO.setup(ReedPin, GPIO.IN, pull_up_down=GPIO.PUD_UP)    # Set ReedPin's mode is input, and pull up to high level(3.3V)
        GPIO.add_event_detect(ReedPin, GPIO.BOTH, callback=detect, bouncetime=200)

    def Led(x):
        if x == 0:
            GPIO.output(Rpin, 1)
            GPIO.output(Gpin, 0)
        if x == 1:
            GPIO.output(Rpin, 0)
            GPIO.output(Gpin, 1)

    def detect(self):
        Led(GPIO.input(ReedPin))

    def loop():
        while True:
            pass

    def destroy():
        GPIO.output(Gpin, GPIO.HIGH)       # Green led on
        GPIO.output(Rpin, GPIO.LOW)       # Red led off
        GPIO.cleanup()                     # Release resource

    if __name__ == '__main__':     # Program start from here
        setup()
        detect()
        try:
            loop()
        except KeyboardInterrupt:  # When 'Ctrl+C' is pressed, the child program destroy() will be  executed.
            destroy()

**Code Explanation**

.. code-block:: python

    ReedPin = 17
    Gpin    = 27
    Rpin    = 22

    def setup():
        GPIO.setmode(GPIO.BCM)       # 
        GPIO.setup(Gpin, GPIO.OUT)     # Set Green Led Pin mode to output
        GPIO.setup(Rpin, GPIO.OUT)     # Set Red Led Pin mode to output
        GPIO.setup(ReedPin, GPIO.IN, pull_up_down=GPIO.PUD_UP)    # Set ReedPin's mode is input, and pull up to high level(3.3V)
        GPIO.add_event_detect(ReedPin, GPIO.BOTH, callback=detect, bouncetime=200)

Set the GPIO modes to BCM Numbering. ``ReedPin``, ``Gpin`` and ``Rpin`` connects to the GPIO17, GPIO27 and GPIO22.

``GPIO.add_event_detect()`` is used to add an event that is triggered by a change in the value (level) of ``ReedPin``, at which point the callback function ``detect()`` is called.

.. code-block:: python

    def Led(x):
        if x == 0:
            GPIO.output(Rpin, 1)
            GPIO.output(Gpin, 0)
        if x == 1:
            GPIO.output(Rpin, 0)
            GPIO.output(Gpin, 1)

Define a function ``Led()`` to turn the two LEDs on or off. If ``x=0``, the red LED lights up; otherwise, the green LED will be lit.

.. code-block:: python

    def detect(self):
    Led(GPIO.input(ReedPin))

In this callback function, the value of the reed switch is used to control the 2 LEDs.

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

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