GPIO and Python (8/9) - LDR

By The Pi HutOct 21, 20130 comments

In this project you will learn how to wire and program a light sensor and see how bright it is in your room.

Things you will need:

Raspberry Pi + SD Card
Keyboard + Mouse
Monitor + HDMI Cable
Power Supply
Breadboard
1x Red LED
1x Blue LED
2x 330? Resistor
5x M/M Jumper Wire
8x M/F Jumper Wire
1x Button
1x Buzzer
1x DS18B20 Temperature Sensor
1x 4k7? Resistor
1x 1uF Capacitor
1x Light Dependent Resistor (LDR)

Prerequisites:

Latest version of Rasbian installed on your SD Card
Raspberry Pi setup with a keyboard, mouse and monitor

1. Change the current directory to our gpio_python_code directory:

cd gpio_python_code

2. Start by creating a file for our ldr script

 touch 8_ldr.py

3. We will also need another file for logging data to, lets create a file called foo.txt (you can all this what you like)

touch foo.txt

4. Edit the 8_ldr.py script using nano 8_ldr.py add the following code:

#!/usr/bin/python



import os

import datetime

from time import sleep

import RPi.GPIO as GPIO



GPIO.setmode(GPIO.BCM)



def RCtime (RCpin):

    reading = 0

    GPIO.setup(RCpin, GPIO.OUT)

    GPIO.output(RCpin, GPIO.LOW)

    sleep(.1)



    GPIO.setup(RCpin, GPIO.IN)

    # This takes about 1 millisecond per loop cycle

    while (GPIO.input(RCpin) == GPIO.LOW):

        reading += 1

    return reading



while True: 

    GetDateTime = datetime.datetime.now().strftime("%Y-%m-%d %H:%M:%S")

    LDRReading = RCtime(3)

    print RCtime(3)



    # Open a file

    fo = open("/home/pi/gpio_python_code/foo.txt", "wb")

    fo.write (GetDateTime)

    LDRReading = str(LDRReading)

    fo.write ("
")

    fo.write (LDRReading)



    # Close opend file

    fo.close()

    sleep(1)