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.
BCD 7-segment decoder
Model: 74LS47N (datasheet download)
All output pins are active LOW
Array resistor (B331J)
Option 1. Connecting with a BCD 7-segment decoder
Option 2. Connecting without a 7-segment decoder
Circuit Configuration
Example Code
Download the tutorial code
TU_GPIO_LED_7segment_student.cClick here for downloadProgram 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
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.
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
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]
}
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