My first Arduino project.

After reading several books and testing few basic things with my first Arduino kit I decided to try to realize a simple project: a bar graph made of LEDs controlled by a light sensor. Nothing fancy or very original, but I needed something to start!

This is what I used for this project:

• 1x Arduino Uno
• 1x large 700 tie-points breadboard
• 5x 3mm red LEDs
• 5x 220Ω resistors
• 1x LDR light sensor
• 1x 10kΩ resistor
• 9x jumper wires (male-male)

The project is divided in 2 main units: a light sensor measuring the light intensity of the environment (right of Pic1) and a bar graph made of 5 red LEDs 

I’m using 2 levels of brightness (full and 1/4) for every LED, so the bar graph can represents 10 levels of light intensity (f.e.: light level 5 ==> LEDs 1,2 ON full brightness, LED 3 ON 1/4 brightness, LEDs 4,5 OFF).

When starting the device in a dark room no LED is ON,

And obviously exposing the sensor to a close lamp turns more LEDs ON,

The sketch I wrote to control this device is pretty simple and the (many) comments should make it clear to everybody.

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// === CONSTANTS === // -- INPUT -- const int PIN_SENSOR = 0; // -- OUTPUT -- const int NUM_LEDS = 5; const int PIN_LEDS[NUM_LEDS] = { 3, 5, 6, 9, 10 }; // === CONSTANTS END === // === INITIALIZATION === void setup() {   // initialize serial communication at 9600 bits per second   Serial.begin(9600); } // === INITIALIZATION END === // === MAIN LOOP === void loop() {   // read the value from the LDR and convert it into a [0-10] range   int light_val = analogRead(PIN_SENSOR);   int light_lvl = light_val / 102;   // number of full-LEDs ON   int leds_on = light_lvl / 2;   // DEBUG   Serial.print("light_val: ");   Serial.print(light_val);   Serial.print(" -> light_lvl: ");   Serial.print(light_lvl);   Serial.print(" -> leds_on: ");   Serial.println(leds_on);   int i;   // turn LEDs ON - full brightness   for(i = 0; i < leds_on; i++)     analogWrite(PIN_LEDS[i], 255);   // light level is odd -> turn one more LED ON - 1/4 brightness   if(light_lvl % 2)   {     analogWrite(PIN_LEDS[i], 64);     i++;   }   // turn remaining LEDs OFF   for(; i < NUM_LEDS; i++)     analogWrite(PIN_LEDS[i], 0);   // 10 FPS   delay(100); } // === MAIN LOOP END ===

This sketch is also using the serial port to print some debug output, but that code (lines 14 and 28-33) is totally optional and could be deleted without affecting the functionality of the device.