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.. _2.2.6_py:

2.2.6 Speed Sensor Module
=========================

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

In this project, we will learn the use of the speed sensor module. A Speed sensor module is a type of tachometer that is used to measure the speed of a rotating object like a motor.

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

In this project, we need the following components. 

.. image:: ../img/2.2.6component.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_speed_sensor`
        - \-

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

.. image:: ../img/2.2.6circuit.png
    :width: 400
    :align: center

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

**Step 1:** Build the circuit.

.. image:: ../img/2.2.6fritzing.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 2.2.6_speed_sensor_module.py

After the code runs, the green LED will light up. If you place an obstacle in the gap of the speed sensor module, the "light blocked" will be printed on the screen and the red LED will be lit.
Remove the obstacle and the green LED will light 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

    speedPin  = 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(speedPin, GPIO.IN, pull_up_down=GPIO.PUD_UP)    # Set speedPin's mode is input, and pull up to high level(3.3V)
        GPIO.add_event_detect(speedPin, GPIO.BOTH, callback=detect, bouncetime=200)

    def Led(x):
        if x == 0:
            GPIO.output(Rpin, 0)
            GPIO.output(Gpin, 1)
        if x == 1:
            GPIO.output(Rpin, 1)
            GPIO.output(Gpin, 0)
            print ('Light was blocked')
            
    def detect(chn):
        Led(GPIO.input(speedPin))

    def loop():
        while True:
            pass

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

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

**Code Explanation**

.. code-block:: python

    GPIO.add_event_detect(speedPin, GPIO.BOTH, callback=detect, bouncetime=200)

Add an event here, triggered by a change in the level of ``speedPin`` and call ``detect()`` to control the 2 LEDs on and off.

.. code-block:: python

    def Led(x):
        if x == 0:
            GPIO.output(Rpin, 0)
            GPIO.output(Gpin, 1)
        if x == 1:
            GPIO.output(Rpin, 1)
            GPIO.output(Gpin, 0)
            print ('Light was blocked')			

Define a function ``Led()`` that turns the red LED on and prints ``Light was blocked`` when the parameter is 1; turn the green LED on when the parameter is 0.

.. code-block:: python

    def detect(chn):
        Led(GPIO.input(speedPin))

Define a callback function where the value of ``speedPin`` will control the turning on or off of the 2 LEDs.



**Phenomenon Picture**
-----------------------

.. image:: ../img/2.2.6photo_interrrupter.JPG
   :width: 500
   :align: center