Adaptive Screen Brightness using LDR and Python script

Requirements:

1. Arduino with Atmega328p

2. LDR

3. Python 2.7 on your machine

4. Python libraries: Pyserial

Summary:

Ever wondered how useful is the automatic brightness feature on phones? It can quickly alter screen’s brightness according to the surrounding light intensity.

In this project I have tried to create something similar for any PC or Laptop running on Linux (preferably Ubuntu 14.04).

My goal was to keep it affordable and simple as much as possible.

So to make its prototype, I used LDR to measure light intensity and an Arduino to communicate with my machine. On my machine I used a python script to communicate over USB with Arduino and to edit the file which is responsible for the brightness of screen.

This project costs around Rs 300 just because of microcontroller that is being used (needless to say it’s a prototype). It has got very high utility, especially for PC users.

To get more detailed information on controlling brightness using terminal, you can checkout this link.

And to get more detailed references on atmega328p you can checkout Atmega328p documentation.

Description:

How I am uploading code on arduino:

f = <source_code’s_file_name>

avr-gcc -g -mmcu=atmega328p -Wall -Os $(f).c -o $(f).elf

avr-objcopy -j .text -j .data -O ihex $(f).elf $(f).hex

sudo avrdude -F -V -c arduino -p m328p -P /dev/ttyUSB* -b 57600 -e -U flash:w:$(f).hex

Just type these four commands, in the same order, in your terminal and remember to put the source code’s filename in variable “f”. These commands are for Linux users only.

First command stores the filename in variable “f”, second command is used to convert source code to .elf file, third command is used to convert that .elf file to .hex file which can be uploaded on atmega328p, and the fourth command is used to upload that .hex file.

Little bit about LDR that is being used

LDR stands for Light Dependent Resistor. Its resistance has an inverse relationship with luminous intensity. Generally, it has very high resistance somewhere around 1000 Kohms but when light falls on it, it decreases dramatically by few hundred ohms. LDR is an inexpensive device which finds its way in many of our day to day applications.

Explaination of Source Code

This program is an application of ADC and serial communication.

Before reading this article, check out the explanation about ADC here.

There are few changes that I made in setup_adc() function and ISR() block.

In setup_adc() function I set the MUX1 bit in ADMUX register in order to start the conversion of value at PORTC2.

In ISR() block, I first stored 10-bit value from ADC in a variable(ldrValue). Then using conditional statements I mapped “ldrValue” to three levels of brightness:

a. minimum_brightness = 500

b. medium_brightness = 2500

c. maximum_brightness = 4880

*You might need to change them according to your machine.

I have used uartLibrary.h to send brightness value and ldr value to my laptop using serial communication. I built this library referring to this article . After including this library I can use printf() function from stdio.h to send strings from atmega328p to my laptop.

I put all code files in a .zip folder

For detailed information please check the Source Code it’s very well documented.

Explanation of Python Script

I’m using pyserial libraries for serial communication, it’s freely available.

Python script needs root permission to run properly; else it will display an error message and exit.

Once it gets the root permission it creates an object “ser” of “Serial” class and takes two arguments in it:

a. Serial Port: In my case it is ‘/dev/ttyUSB0’

b. Baud rate: In my case it is 9600

Then, it sets the file path in a variable (path).

*You might need to edit them according to your machine.

Then in an infinite loop, I put a try & except block just to take care of initial garbage values.

In try block, a variable (value) stores the list of two strings, one is the brightness value other is the LDR value.

After that it opens the file given in “path” variable in write mode and writes the brightness value in it. Then it saves and closes the file.

And for debugging purpose, it prints the list with brightness and ldr value.

For more information, you can also check this link changing brightness through terminal.

Fig. 1: Typical Image of Arduino Uno used for Automatic Control of LED Monitor’s Brightness

Fig. 2: Typical Image of Arduino Uno

Project Source Code

###
/////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
//                                                          Varun13169                                                                //
/////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
 
#define F_CPU           16000000UL
#include "uartLibrary.h"
#include 
#include 
#include 
#include 
 
 
/****************** Limits **************/
#define low_min 0
#define low_max 10
 
#define mid_min 10
#define mid_max 30
 
#define high_min 30
 
#define minimum_brightness 500
#define medium_brightness 2500
#define maximum_brightness 4880
/****************************************/
/*
 You might need to change these limits
 according to your Linux machine and LDR
*/
 
 
int ldrValue=0;
void setup_adc();
 
int main(void)
{ 
    uart_init();
    stdout = &uart_output;
    stdin  = &uart_input;
   
    DDRC |= 0x0A;                  // Set Pin5 and Pin7 on arduino as output
    PORTC = 1<
   
    sei();                        // Enales global interrupt
    setup_adc();            // Setup ADC according to the defined function
             
    while(1)
    {
    }
}
 
 
 
void setup_adc()
{
    ADCSRA |= 1<
    ADCSRA |= 1<
    ADCSRA |=  1<
    ADMUX |= 1<
    //ADLAR=1 for left adjusted result and REFS0=1 with REFS1=0 to use Vcc as reference voltage
    //MUX1=1 because we want to start conversion from PORTC2
    DIDR0 |= 1<
}
 
 
/*********** varun13169 **************/
 
 
/******************************************** ISR Block ********************************************/
ISR(ADC_vect)
{
    uint8_t adcl = ADCL;                                  //This is an 8-bit varible used to store the value of ADLC
    uint16_t adc_ten_bit_value = ADCH<<2 | adcl>>6;  //This is an 16-bit varible use to store the 10-bit value of left adjusted result
   
    ldrValue=adc_ten_bit_value;
   
    if(low_min<=ldrValue && ldrValue
    if(mid_min<=ldrValue && ldrValue
    if(ldrValue>=high_min){printf("%d %dn", maximum_brightness, ldrValue);}                    // to my laptop
 
    ADCSRA |= 1<
}
/***************************************************************************************************/
 
 
/*********************************************************** END *******************************************************************/
###