LED Chaser Controlled by LDR (Light Dependent Resistor)

Hello all ! Today in this blog we will discuss about how to control 8 LED’s using Arduino and a shift register and a LDR through programming. Arduino is an open source electronic platform based on easy to use hardware and software.

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Components

Circuit Diagram

8ledsshiftreg

Shift Register

Here we have used Serial-In-Parallel-Out shift register IC 74HC595. We can control any number of output pins using only 3 input pins of shift register called Data, Clock and Latch. Here we have used 8 number of LED’s so we would have needed 8 number of input pins but no we can control these 8 LED’s using only 3 input pins of shift register.

74hc595

Code

/*
Arduino Tutorial - Lesson 4. 8 LEDs and a Shift Register
*/
int dataPin = 4; //shift register pin14
int clockPin = 5; //shift register pin11
int latchPin = 6; //shift register pin12

byte leds = 0;

void setup() 
{
  pinMode(latchPin, OUTPUT);
  pinMode(dataPin, OUTPUT);  
  pinMode(clockPin, OUTPUT);
}

void loop() 
{
  leds = 0;
  updateShiftRegister();
  delay(500);
  for (int i = 0; i < 8; i++)
  {
    bitSet(leds, i);
    updateShiftRegister();
    delay(250);
  }
}

void updateShiftRegister()
{
   digitalWrite(latchPin, LOW);
   shiftOut(dataPin, clockPin, LSBFIRST, leds);
   digitalWrite(latchPin, HIGH);
}

Code to Note

pinMode(4, OUTPUT) – You have to tell ARDUINO that PIN4, PIN5 and PIN6 are used as Output or Input. so, here we used the built in function called pinMode().

updateShiftRegister() – Shift Register has 8 Bits so every time we have to send 8 Bits data to 74HC595 Shift Register IC through Arduino using built in function bitset(). Before sending these 8 Bits data to 74HC595 IC we have to triggered the Latch pin to LOW and after sending these 8 Bits data we have to triggered the Latch pin to HIGH.

Result

In this program 8 LED’s glowing one by one gradually. Similarly we can also reprogram the ARDUINO and change the rate at which it glows.

Further Readings

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