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2.2.1 Photoresistor

Introduction

Photoresistor is a commonly used component of ambient light intensity in life. It helps the controller to recognize day and night and realize light control functions such as night lamp. This project is very similar to potentiometer, and you might think it changing the voltage to sensing light.

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
ADC0834	-
Photoresistor	BUY

Schematic Diagram

Experimental Procedures

Step 1: Build the circuit.

Step 2: Go to the folder of the code.

cd ~/raphael-kit/python-pi5

Step 3: Run the executable file.

sudo python3 2.2.1_Photoresistor_zero.py

When the code is running, the brightness of the LED will change according to the light intensity sensed by the photoresistor.

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 PWMLED
import ADC0834
import time

# Initialize a PWM LED on GPIO pin 22
led = PWMLED(22)

# Set up the ADC0834 module
ADC0834.setup()

# Define a function for mapping values from one range to another
def MAP(x, in_min, in_max, out_min, out_max):
    return (x - in_min) * (out_max - out_min) / (in_max - in_min) + out_min

# Main loop for reading ADC value and controlling LED brightness
def loop():
    while True:
        # Read analog value from ADC
        analogVal = ADC0834.getResult()
        print('value = %d' % analogVal)

        # Map the ADC value to a PWM value and set LED brightness
        led.value = float(analogVal/255)

        # Wait for 0.2 seconds
        time.sleep(0.2)

# Run the main loop and handle KeyboardInterrupt for graceful shutdown
try:
    loop()
except KeyboardInterrupt:
    # Turn off LED before exiting
    led.value = 0

Code Explanation

1. This segment imports the PWMLED class from the gpiozero library, necessary for controlling PWM LEDs. It also includes the ADC0834 module for interfacing with the analog-to-digital converter, and the time module for executing time-based functions such as sleep.

   #!/usr/bin/env python3
   from gpiozero import PWMLED
   import ADC0834
   import time
   

2. Initializes a PWM LED connected to GPIO pin 22 and sets up the ADC0834 module, preparing it for use in the project.

   # Initialize a PWM LED on GPIO pin 22
   led = PWMLED(22)
   
   # Set up the ADC0834 module
   ADC0834.setup()
   

3. Defines a function to map an input value from one range to another. This function is crucial for translating the ADC readings into a suitable range for PWM control.

   # Define a function for mapping values from one range to another
   def MAP(x, in_min, in_max, out_min, out_max):
       return (x - in_min) * (out_max - out_min) / (in_max - in_min) + out_min
   

4. This section contains a loop that continuously reads the analog value from the ADC0834, maps it to a corresponding PWM value, and adjusts the LED brightness. A brief delay (time.sleep(0.2)) is included to make the changes visible and to avoid overburdening the CPU.

   # Main loop for reading ADC value and controlling LED brightness
   def loop():
       while True:
           # Read analog value from ADC
           analogVal = ADC0834.getResult()
           print('value = %d' % analogVal)
   
           # Map the ADC value to a PWM value and set LED brightness
           led.value = float(analogVal/255)
   
           # Wait for 0.2 seconds
           time.sleep(0.2)
   

5. Executes the loop function and includes error handling for a graceful shutdown on KeyboardInterrupt. It ensures the LED is turned off when the program is stopped.

   # Run the main loop and handle KeyboardInterrupt for graceful shutdown
   try:
       loop()
   except KeyboardInterrupt:
       # Turn off LED before exiting
       led.value = 0