A 7-segment display is a device that can display numerals and letters. It's made up of seven LEDs connected in parallel. Different letters/numbers can be shown by connecting pins on the display to the power source and enabling the related pins, thus turning on the corresponding LED segments. In this lesson let's learn how to display specific characters on it.

Step 1: Components

- Arduino Uno board * 1

- USB cable * 1

- 74HC595 *1

- Resistor (220Ω) * 8

- 7-Segment display

- Breadboard * 1

- Jumper wires

Step 2: Principle

The 74HC595 consists of an 8−bit shift register and a storage register with three−state parallel outputs. It converts serial input into parallel output so you can save IO ports of an MCU.

When MR (pin10) is high level and OE (pin13) is low level, data is input in the rising edge of SHcp and goes to the memory register through the rising edge of SHcp. If the two clocks are connected together, the shift register is always one pulse earlier than the memory register. There is a serial shift input pin (Ds), a serial output pin (Q) and an asynchronous reset button (low level) in the memory register. The memory register outputs a Bus with a parallel 8-bit and in three states. When OE is enabled (low level), the data in memory register is output to the bus.

Pins of 74HC595 and their functions:

Q0-Q7: 8-bit parallel data output pins, able to control 8 LEDs or 8 pins of 7-segment display directly.

Q7’: Series output pin, connected to DS of another 74HC595 to connect multiple 74HC595s in series

MR: Reset pin, active at low level; here it is directly connected to 5V.

SHcp: Time sequence input of shift register. On the rising edge, the data in shift register moves successively one bit, i.e. data in Q1 moves to Q2, and so forth. While on the falling edge, the data in shift register remain unchanged.

STcp: Time sequence input of storage register. On the rising edge, data in the shift register moves into memory register.

OE: Output enable pin, active at low level. Here connected to GND.

DS: Serial data input pin

VCC: Positive supply voltage

GND: Ground

Step 3: The Schematic Diagram

Step 4: Procedures

In this experiment MR (pin10) is connected to 5V (HIGH Level) and OE (pin 13) to GND (LOW Level). Therefore, the data is input into the rising edge of SHcp and enters the memory register through the rising edge. We use the shiftout() function to output a 8-bit data to the shift register through DS. In the rising edge of the SHcp, the data in the shift register moves successively one bit in one time, i.e. data in Q1 moves to Q2, and so forth. In the rising edge of STcp, data in the shift register moves into the memory register. All data will be moved to the memory register after 8 times. Then the data in the memory register is output to the bus (Q0-Q7). So the 16 characters are displayed in the 7-segment in turn.

Step 1:

Build the circuit.

Step 2:

Download the code from https://github.com/primerobotics/Arduino

Step 3:

Upload the sketch to the Arduino Uno board

Click the Upload icon to upload the code to the control board.

If "Done uploading" appears at
the bottom of the window, it means the sketch has been successfully uploaded.

You should now see the 7-segment display from 0 to 9 and A to F.

Step 5: Code

//74HC595
//You should now
be able to see the 7-segment display cycle from 0 to F
//Email:info@primerobotics.in
//Website:www.primerobotics.in
const int STcp =
12;//Pin connected to ST_CP of 74HC595
const int SHcp =
8;//Pin connected to SH_CP of 74HC595 
const int DS = 11;
//Pin connected to DS of 74HC595 
//display 0,1,2,3,4,5,6,7,8,9,A,b,C,d,E,F
int datArray[16] =
{252, 96, 218, 242, 102, 182, 190, 224, 254, 246, 238, 62, 156, 122, 158, 142};
void setup ()
{
  //set pins to output
  pinMode(STcp,OUTPUT);
  pinMode(SHcp,OUTPUT);
  pinMode(DS,OUTPUT);
}
void loop()
{
  //loop from 0 to 256
  for(int num = 0; num < 16; num++)
  {
    digitalWrite(STcp,LOW); //ground ST_CP and
hold low for as long as you are transmitting
    shiftOut(DS,SHcp,MSBFIRST,datArray[num]);
    //return the latch pin high to signal chip
that it 
    //no longer needs to listen for information
    digitalWrite(STcp,HIGH); //pull the
ST_CPST_CP to save the data
    delay(1000); //wait for a second
  }
}