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/

Step 3: Run the executable file.

sudo python3 2.2.1_Photoresistor.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. After modifying the code, you can run it directly to see the effect.

#!/usr/bin/env python3
import RPi.GPIO as GPIO
import ADC0834
import time
LedPin = 22
def setup():
    global led_val
    # Set the GPIO modes to BCM Numbering
    GPIO.setmode(GPIO.BCM)
    # Set all LedPin's mode to output and initial level to High(3.3v)
    GPIO.setup(LedPin, GPIO.OUT, initial=GPIO.HIGH)
    ADC0834.setup()
    # Set led as pwm channel and frequece to 2KHz
    led_val = GPIO.PWM(LedPin, 2000)
    # Set all begin with value 0
    led_val.start(0)
def destroy():
    # Stop all pwm channel
    led_val.stop()
    # Release resource
    GPIO.cleanup()
def loop():
    while True:
        analogVal = ADC0834.getResult()
        print ('analog value = %d' % analogVal)
        led_val.ChangeDutyCycle(analogVal*100/255)
        time.sleep(0.2)
if __name__ == '__main__':
    setup()
    try:
        loop()
    except KeyboardInterrupt: # When 'Ctrl+C' is pressed, the program destroy() will be executed.
        destroy()

Code Explanation

def loop():
    while True:
        analogVal = ADC0834.getResult()
        print ('analog value = %d' % analogVal)
        led_val.ChangeDutyCycle(analogVal*100/255)
        time.sleep(0.2)

Read the analog value of CH0 of ADC0834. By default, the function getResult() is used to read the value of CH0, so if you want to read other channels, please input 1, 2, or 3 into () of the function getResult(). Next, what you need is to print the value via the print function. Because the changing element is the duty cycle of LedPin, the computational formula, analogVal*100/255 is needed to convert analogVal into percentage. Finally, ChangeDutyCycle() is called to write the percentage into LedPin.