Arduino Tutorial 5 : Serial Communication

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

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Circuit Diagram


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.



Created By Ratnadeep - Lesson 5. Serial Monitor

int latchPin = 6; //Shift Register's pin12
int clockPin = 5; //Shift Register's pin11
int dataPin = 4;  //Shift Register's pin14

byte leds = 0;

void setup() 
  pinMode(latchPin, OUTPUT);
  pinMode(dataPin, OUTPUT);  
  pinMode(clockPin, OUTPUT);
  while (! Serial); // Wait untilSerial is ready 
  Serial.println("Enter LED Number 0 to 7 or 'x' to clear");

void loop() 
  if (Serial.available())
    char ch =;
    if (ch >= '0' && ch <= '7')
      int led = ch - '0';
      bitSet(leds, led);
      Serial.print("Turned on LED ");
    if (ch == 'x')
      leds = 0;

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.


In this program 8 LED’s can be controlled by serial Monitor. When we type 0 first LED will ON and when we type 7 eighth LED will ON and when we type X all LED will turn OFF. Similarly we can also reprogram the ARDUINO and change the key at which it ON or OFF.

Further Readings

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