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2.2.5 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.

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

Name	ITEMS IN THIS KIT	LINK
Raphael Kit	337	Raphael Kit

You can also buy them separately from the links below.

COMPONENT INTRODUCTION	PURCHASE LINK
GPIO Extension Board	BUY
Breadboard	BUY
Jumper Wires	BUY
Resistor	BUY
LED	BUY
Speed Sensor Module	-

Schematic Diagram

Experimental Procedures

Step 1: Build the circuit.

Step 2: Change directory.

cd ~/raphael-kit/python-pi5

Step 3: Run.

sudo python3 2.2.6_speed_sensor_module_zero.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-pi5. After modifying the code, you can run it directly to see the effect.

#!/usr/bin/env python3
from gpiozero import LED, Button
from signal import pause

# Initialize GPIO pins for the speed sensor and LEDs using GPIO Zero library
speed_sensor = Button(17, pull_up=False)  # Speed sensor connected to GPIO pin 17 without pull-up
green_led = LED(27)                      # Green LED connected to GPIO pin 27
red_led = LED(22)                        # Red LED connected to GPIO pin 22

def update_leds():
    """
    Update the state of LEDs based on the speed sensor.
    - If the sensor is pressed (triggered), the red LED is turned on and a message is printed.
    - If the sensor is released (not triggered), the green LED is turned on.
    """
    if speed_sensor.is_pressed:
        green_led.off()  # Turn off green LED
        red_led.on()     # Turn on red LED
        print('Light was blocked')  # Print message indicating sensor is triggered
    else:
        green_led.on()   # Turn on green LED
        red_led.off()    # Turn off red LED

try:
    # Main loop to continuously check sensor state
    while True:
        # Update LEDs based on sensor state changes
        speed_sensor.when_pressed = update_leds   # Update LEDs when sensor is pressed
        speed_sensor.when_released = update_leds  # Update LEDs when sensor is released

except KeyboardInterrupt:
    # Handle KeyboardInterrupt (Ctrl+C) for a graceful script termination
    pass

Code Explanation

1. The gpiozero library is imported to use its LED and Button classes for interacting with the GPIO pins. The signal library is imported for the pause function, which is used to keep the script running.

   #!/usr/bin/env python3
   from gpiozero import LED, Button
   from signal import pause
   

2. speed_sensor is set as a Button on GPIO pin 17. The pull_up=False parameter indicates that the internal pull-up resistor is not used. green_led and red_led are initialized as LED objects connected to GPIO pins 27 and 22, respectively.

   # Initialize GPIO pins for the speed sensor and LEDs using GPIO Zero library
   speed_sensor = Button(17, pull_up=False)  # Speed sensor connected to GPIO pin 17 without pull-up
   green_led = LED(27)                      # Green LED connected to GPIO pin 27
   red_led = LED(22)                        # Red LED connected to GPIO pin 22
   

3. The update_leds function checks the state of the speed sensor. If the sensor is pressed (activated), it turns off the green LED, turns on the red LED, and prints a message. If the sensor is released, it does the opposite.

   def update_leds():
       """
       Update the state of LEDs based on the speed sensor.
       - If the sensor is pressed (triggered), the red LED is turned on and a message is printed.
       - If the sensor is released (not triggered), the green LED is turned on.
       """
       if speed_sensor.is_pressed:
           green_led.off()  # Turn off green LED
           red_led.on()     # Turn on red LED
           print('Light was blocked')  # Print message indicating sensor is triggered
       else:
           green_led.on()   # Turn on green LED
           red_led.off()    # Turn off red LED
   

4. The main loop continuously checks the state of the speed sensor. The when_pressed and when_released attributes are event handlers that call the update_leds function when the sensor state changes. The try-except block is for handling a KeyboardInterrupt for a graceful exit.

   try:
       # Main loop to continuously check sensor state
       while True:
           # Update LEDs based on sensor state changes
           speed_sensor.when_pressed = update_leds   # Update LEDs when sensor is pressed
           speed_sensor.when_released = update_leds  # Update LEDs when sensor is released
   
   except KeyboardInterrupt:
       # Handle KeyboardInterrupt (Ctrl+C) for a graceful script termination
       pass