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.. _1.3.3_c:

1.3.3 Relay
=================

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

In this project, we will learn to use a relay. It is one of the commonly
used components in automatic control system. When the voltage, current,
temperature, pressure, etc., reaches, exceeds or is lower than the
predetermined value, the relay will connect or interrupt the circuit, to
control and protect the equipment.

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

In this project, we need the following components. 

.. image:: ../img/list_1.3.4.png

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_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_transistor`
        - |link_transistor_buy|
    *   - :ref:`cpn_relay`
        - |link_relay_buy|
    *   - :ref:`cpn_diode`
        - |link_diode_buy|

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

.. image:: ../img/image345.png


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

**Step 1:** Build the circuit.

.. image:: ../img/image144.png

**Step 2**: Open the code file.

.. raw:: html

   <run></run>

.. code-block::

    cd ~/raphael-kit/c/1.3.3

**Step 3:** Compile the code.

.. raw:: html

   <run></run>

.. code-block::

    gcc 1.3.3_Relay.c -lwiringPi


**Step 4:** Run the executable file.

.. raw:: html

   <run></run>

.. code-block::

    sudo ./a.out

After the code runs, the LED will light up. In addition, you can
hear a ticktock caused by breaking normally close contact and 
closing normally open contact.

.. 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 RelayPin 0

    int main(void){
        if(wiringPiSetup() == -1){ //when initialize wiring failed, print message to screen
            printf("setup wiringPi failed !");
            return 1;
        }
        pinMode(RelayPin, OUTPUT);   //set GPIO17(GPIO0) output
        while(1){
            // Tick
            printf("Relay Open......\n");
            digitalWrite(RelayPin, LOW);
            delay(1000);
            // Tock
            printf("......Relay Close\n");
            digitalWrite(RelayPin, HIGH);
            delay(1000);
        }

        return 0;
    }

**Code Explanation**

.. code-block:: c

    digitalWrite(RelayPin, LOW);

Set the I/O port as low level (0V), thus the transistor is not energized
and the coil is not powered. There is no electromagnetic force, so the
relay opens, LED does not turn on.

.. code-block:: c

    digitalWrite(RelayPin, HIGH);

set the I/O port as high level (5V) to energize the transistor. The coil
of the relay is powered and generate electromagnetic force, and the
relay closes, LED lights up.

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

.. image:: ../img/image145.jpeg