Note

Hello, welcome to the SunFounder Raspberry Pi & Arduino & ESP32 Enthusiasts Community on Facebook! Dive deeper into Raspberry Pi, Arduino, and ESP32 with fellow enthusiasts.

Why Join?

• Expert Support: Solve post-sale issues and technical challenges with help from our community and team.

• Learn & Share: Exchange tips and tutorials to enhance your skills.

• Exclusive Previews: Get early access to new product announcements and sneak peeks.

• Special Discounts: Enjoy exclusive discounts on our newest products.

• Festive Promotions and Giveaways: Take part in giveaways and holiday promotions.

👉 Ready to explore and create with us? Click [here] and join today!

2.2.1 Photoresistor(MCP3008)

Note

Depending on your kit version, please identify whether you have ADC0834 or MCP3008 and proceed with the matching section.

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
MCP3008	-
Photoresistor	BUY

Schematic Diagram

T-Board Name	physical	WiringPi	BCM
SPICE0	pin24	10	8
SPIMOSI	pin19	12	10
SPIMISO	pin21	13	9
SPISCLK	pin23	14	11
GPIO22	pin15	3	22

Experimental Procedures

Step 1: Build the circuit.

Step 2: Set up the SPI interface and install the spidev library (see SPI Configuration for detailed instructions). If you have already completed these steps, you can skip this.

Step 3: Go to the folder of the code.

cd ~/raphael-kit/python

Step 4: Run the executable file.

sudo python3 2.2.1-2_photoresistor.py

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

Warning

If there is an error prompt RuntimeError: Cannot determine SOC peripheral base address, please refer to If gpiozero doesn’t work.

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.

#!/usr/bin/env python3

import RPi.GPIO as GPIO
import spidev
import time

# GPIO pin for PWM LED
PWM_PIN = 22

# Setup GPIO
GPIO.setmode(GPIO.BCM)
GPIO.setup(PWM_PIN, GPIO.OUT)

# Initialize PWM (frequency = 1000Hz)
pwm = GPIO.PWM(PWM_PIN, 1000)
pwm.start(0)  # Start with 0% duty cycle

# Initialize SPI (MCP3008 on Bus 0, CE0)
spi = spidev.SpiDev()
spi.open(0, 0)
spi.max_speed_hz = 1000000  # 1 MHz

# Function to read MCP3008 ADC value
def read_adc(channel):
    """
    Read analog value from MCP3008 (channel 0–7)
    Returns: 10-bit value (0–1023)
    """
    if channel < 0 or channel > 7:
        return -1
    r = spi.xfer2([1, (8 + channel) << 4, 0])
    value = ((r[1] & 3) << 8) | r[2]
    return value

# Main loop to read ADC and set PWM brightness
try:
    while True:
        analogVal = read_adc(0)
        print(f"value = {analogVal}")

        # Scale ADC value (0–1023) to duty cycle (0–100)
        duty_cycle = analogVal * 100 / 1023
        pwm.ChangeDutyCycle(duty_cycle)

        time.sleep(0.2)

except KeyboardInterrupt:
    pass

finally:
    pwm.stop()
    GPIO.cleanup()
    spi.close()

Code Explanation

1. Import necessary libraries:

   • RPi.GPIO to control GPIO pins and generate PWM signal.

   • spidev to interface with the MCP3008 ADC via SPI.

   • time to handle timing and delays.

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

2. Configure GPIO pin 22 as PWM output using BCM mode. Then, initialize software PWM at 1000 Hz with a starting duty cycle of 0%.

   # GPIO pin for PWM LED
   PWM_PIN = 22
   
   # Setup GPIO
   GPIO.setmode(GPIO.BCM)
   GPIO.setup(PWM_PIN, GPIO.OUT)
   
   # Initialize PWM (frequency = 1000Hz)
   pwm = GPIO.PWM(PWM_PIN, 1000)
   pwm.start(0)  # Start with 0% duty cycle
   

3. Set up the SPI interface to communicate with MCP3008 on bus 0, chip enable 0 (CE0), and configure SPI speed to 1 MHz.

   # Initialize SPI (MCP3008 on Bus 0, CE0)
   spi = spidev.SpiDev()
   spi.open(0, 0)
   spi.max_speed_hz = 1000000  # 1 MHz
   

4. Define a function read_adc(channel) to read analog values from MCP3008. The function sends three bytes to the chip and reconstructs a 10-bit analog value (0–1023) from the response.

   # Function to read MCP3008 ADC value
   def read_adc(channel):
       """
       Read analog value from MCP3008 (channel 0–7)
       Returns: 10-bit value (0–1023)
       """
       if channel < 0 or channel > 7:
           return -1
       r = spi.xfer2([1, (8 + channel) << 4, 0])
       value = ((r[1] & 3) << 8) | r[2]
       return value
   

5. This is the main loop that: - Reads analog input from channel 0 of the MCP3008. - Converts the value to a PWM duty cycle (0–100%). - Adjusts the brightness of the LED using pwm.ChangeDutyCycle(). - Repeats every 0.2 seconds.

   # Main loop to read ADC and set PWM brightness
   try:
       while True:
           analogVal = read_adc(0)
           print(f"value = {analogVal}")
   
           # Scale ADC value (0–1023) to duty cycle (0–100)
           duty_cycle = analogVal * 100 / 1023
           pwm.ChangeDutyCycle(duty_cycle)
   
           time.sleep(0.2)
   

6. When the user interrupts the program with Ctrl+C, the PWM and GPIO are properly cleaned up, and the SPI interface is closed.

   except KeyboardInterrupt:
       pass
   
   finally:
       pwm.stop()
       GPIO.cleanup()
       spi.close()