Lesson 16 74HC595

Introduction

In this experiment, you will learn how to use 74HC595 to drive a 7-segment display.

Generally, there are two ways to drive a single 7-segment display. One is to connect its 8 pins directly to eight ports on the SunFounder Uno board, which we have done previously. The other is to connect 74HC595 to three ports of the SunFounder Uno board and connect the 7-segment display to 74HC595. In this experiment, we will use the latter. By this way, you can save five ports. Considering the SunFounder Uno board’s limited ports, this is very important.

 

Components

- 8 * Resistor (220Ω)

- 1 * 74HC595

- 1 * SunFounder Uno board

- Jumper wires

- 1 * Breadboard

- 1 * USB cable

- 1 * 7-segment display

 

Principle

74HC595

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 that you can save IO ports of an MCU. The 74HC595 is widely used to indicate multipath LEDs and drive multi-bit segment displays. "Three-state" refers to the fact that you can set the output pins as either high, low or "high impedance." With data latching, the instant output will not be affected during the shifting; with data output, you can cascade 74HC595s more easily.

 

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.

SH: 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.

ST: 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, connected to GND.

Ds : Serial data input pin

VCC: Positive supply voltage

GND: Ground

Here the shiftout() function is used, which comes with the Arduino IDE. Simply input a number between 0 and 255 and the storage register can convert it into an 8-bit binary number and output it in parallel. This allows you to easily control the 8 pins of the 7-segment display and create any patterns you want.

 

Experimental Procedures

Step 1: Build the circuit

7-Segment Display

74HC595

SunFounder Uno R3

a

Q7

 

b

Q6

 

c

Q5

 

d

Q4

 

e

Q3

 

f

Q2

 

g

Q1

 

DP

Q0

 

 

VCC

5V

 

DS

11

 

CE

GND

 

ST

12

 

SH

8

 

MR

5V

 

Q7’

N/C

 

GND

GND

“ - ”

 

GND

 

 

The schematic diagram

 

Step 2: Program (please go to our official website www.sunfounder.com to download related code by clicking LEARN -> Get Tutorials)

Step 3: Compile the program

Step 4: Burn the program into the SunFounder Uno board

You should now see the 7-segment display cycle from 0 to F.

 

Code

//74HC595
//You should now be able to see the 7-segment display cycle from 0 to F
//Email:support@sunfounder.com
//Website:www.sunfounder.com
//2015.5.7

const int latchPin = 12;//Pin connected to ST_CP of 74HC595
const int clockPin = 8;//Pin connected to SH_CP of 74HC595 
const int dataPin = 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(latchPin,OUTPUT);
  pinMode(clockPin,OUTPUT);
  pinMode(dataPin,OUTPUT);
}
void loop()
{
  //loop from 0 to 256
  for(int num = 0; num < 16; num++)
  {
    digitalWrite(latchPin,LOW); //ground latchPin and hold low for as long as you are transmitting
    shiftOut(dataPin,clockPin,MSBFIRST,datArray[num]);
    //return the latch pin high to signal chip that it 
    //no longer needs to listen for information
    digitalWrite(latchPin,HIGH); //pull the latchPin to save the data
    delay(1000); //wait for a second
  }
}

 

Video

 

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