Tutorial: 7-Segment Display

Using 7-Segment Display in STM32F4

We will learn how to display a decimal number (0~9) on a 7-segment display

• Inputs:

  • Decimal number : 0~9

  • Binary: 4-bit numbers [D C B A] // (0000~ 1001)

• Output:

  • 7-segment decoder: 7-bit numbers ( a to g)

  • 7-segment display: decimal number 0~9

We will learn how to configure the 7-segment display for different options

Option 1. With 7-segment decoder

Option 2. Without using 7-segment decoder

Option 3. Without using 7-segment decoder on JKIT evaluation board

Circuit Description

Hardware Specification

• 7-segment display: common anode (5101ASR)

• 7-segment decoder: 74LS47N (datasheet download)

7-segment display (5101ASR)

For more detail information about 7 segment display - click here

• Common anode: (common pin is connected to VCC)

• Giving ‘LOW’ to the pin -> LED ON

• Needs a load resistor for each pin(led)

Check the difference between the common cathode and common anode.

We will use common anode.

image

BCD 7-segment decoder

Model: 74LS47N (datasheet download)

• All output pins are active LOW

Array resistor (B331J)

array resistor

Option 1. Connecting with a BCD 7-segment decoder

Option 2. Connecting without a 7-segment decoder

Circuit Configuration

image

circuit on breadbord

Example Code

Download the tutorial code

• TU_GPIO_LED_7segment_student.c Click here for download

• Program a function that works as a 7-segment decoder

#include "stm32f4xx.h"
#include "ecRCC2.h"
#include "ecGPIO2.h"

void setup(void);
	
int main(void) {	
	// Initialiization --------------------------------------------------------
	setup();
	
	// Inifinite Loop ----------------------------------------------------------
	while(1){
		GPIO_write(PA_5, LOW);
		GPIO_write(PA_6, LOW);
		GPIO_write(PA_7, HIGH);
		GPIO_write(PB_6, HIGH);
		GPIO_write(PC_7, HIGH);
		GPIO_write(PA_9, LOW);
		GPIO_write(PA_8, LOW);
		GPIO_write(PB_10, LOW);
	}
}

void setup(void){
	RCC_HSI_init();
	GPIO_init(PA_5, OUTPUT);
	GPIO_init(PA_6, OUTPUT);
	GPIO_init(PA_7, OUTPUT);
	GPIO_init(PB_6, OUTPUT);
	GPIO_init(PC_7, OUTPUT);
	GPIO_init(PA_9, OUTPUT);
	GPIO_init(PA_8, OUTPUT);
	GPIO_init(PB_10, OUTPUT);
}

Option 3. Without using a 7-segment decoder on JKIT evaluation board

Circuit Configuration

JKIT - Nucleo 64: link

config

LED Choose

• There are four 7-Segment Displays. You need to choose which one to use.

• There is NO BCD decoder, you need to connect 7-segment display without using decoder.

7-segments display are Common Cathode: Giving 'High' to the pin -> LED on

1. Digital Out: 7-Segment display number	2. Digital Out: Select 7-Segment display
Digital Out	Digital Out
PB_7, PB_6, PB_5, PB_4, PB_3, PB_2, PB_1, PB_0	PC_3, PC_4, PA_11, PA_10
Push-Pull	Push-Pull

Example Code

PinName_t led[8]={PB_7, PB_6, PB_5, PB_4, PB_3, PB_2, PB_1, PB_0};


//each led that has to light up gets a 1, every other led gets a 0
//its in order of the DigitalOut Pins above
int number[11][8]={
                    {1,1,1,0,1,1,1,0},          //zero
                    {0,0,1,0,0,1,0,0},          //one
                    {1,0,1,1,1,0,1,0},          //two
                    {1,0,1,1,0,1,1,0},          //three
                    {0,1,1,1,0,1,0,0},          //four
                    {1,1,0,1,0,1,1,0},          //five
                    {1,1,0,1,1,1,1,0},          //six
                    {1,0,1,0,0,1,0,0},          //seven
                    {1,1,1,1,1,1,1,0},          //eight
                    {1,1,1,1,0,1,1,0},          //nine
                    {0,0,0,0,0,0,0,1}          //dot
                  };


        
//display shows the number in this case 6
int num=6;
for (int i=0; i<8; i++)
    led[i] = number[num][i];

Exercise

Create a simple code that can Select and Display a decimal number (0~9) on 7-segment display (JKIT - Nucleo 64)

• Display Selection and Number

  • (1) Selection of the display: 0~3

  • (2) Decimal Number to display: 0~9

• Output Display:

  • 7-segment displaying a decimal number: 0~9

If you want to display multiple 7-segment displays, you need to use a very short delay to display multiple numbers

Exercise Code

#include "stm32f4xx.h"
#include "ecGPIO2.h"
#include "ecRCC2.h"


// Initialize 7 DOUT pins for 7 segment leds
void seven_seg_FND_init(void); 

// Select display: 0 to 3
// Display a number 0 - 9 only
void seven_seg_FND_display(uint8_t  num, uint8_t select);


void setup(void){
    // Intialize System Clock
    RCC_HSI_init();
    
    // Intialize DOUT Pins      
    // and Others
    // [YOUR CODE GOES HERE]    
    seven_seg_FND_init(); 
};

int main(void) {
    setup();
    uint8 numDisplay=8;
    uint8 selectFND=0;

    while (1) {
        seven_seg_FND_display(numDisplay,selectFND);
    }
}


// Initialize DOUT pins for 7 segment leds
void seven_seg_FND_init(void){	
    //pin name array
    PinName_t pinsFND[12]={PB_7, PB_6, PB_5, PB_4, PB_3, PB_2, PB_1, PB_0, PC_3, PC_4, PA_11, PA_10};
	
    //Iteratively initializing DOUT pins for pinsFND
    // for (int i=0;i<8;i++)
    //    { initialize each pin as output};
    // [YOUR CODE GOES HERE]
    // [YOUR CODE GOES HERE]
}

// Select display: 0 to 3
// Display a number 0 - 9 only
void seven_seg_FND_display(uint8_t  num, uint8_t select){
    // [YOUR CODE GOES HERE]    
    // [YOUR CODE GOES HERE]        
}