Keypad/keyboard
interface to STM32F0
This module explains how to use 4x3 Membrane Keypad with
STM32F0-DISCOVERY microcontroller board
Requirements:
1. 4x3 Membrane Keypad
2. Seven segment display & 3K3ohms resistors
3. Connecting wires.
4. General purpose printed circuit board.
Keypad is an array of switches. Matrix keypads are very
common input devices in embedded systems. They have simple
architecture and are easy to interface. One good thing about
them is that they allow you to interface a large number
of input keys to a microcontroller with minimum usage of
I/O resources. This tutorial type module explains how to
read input data from a 3×4 (12 keys) matrix keypad
interfaced to an ARM Cortex M0 based STM32F0 microcontroller
embedded board and display on a seven segment display. In
short this project is to display the pressed key on the
seven segment display.
Working: There will be 2 wires connected to each
switch of the keypad, they get short circuited whenever
a button is pressed. For example; when button '1' is pressed,
pin PB1 and pin PB2 are connected (as shown in the picture
below). Normally when no switch is pressed there is no connection
between rows and columns. Whenever a button is pressed contact
is made between particular row and column. 4x3 Keypad pin
can be directly connected to microcontroller i/o port of
this board.
Figures above : Keypad logic table and keypad's
row and column pins
Keypad Interfacing circuit: The below circuit connects
4x3 Membrane Keypad with port C and port B of microcontroller.
The 7-segment display is connected to port C and port B
of microcontroller.
Programming: The sample C-program/code below displays
coresponding numbers pressed on the keypad . The text below
in red color-font is the sample code which you can directly
use in your compiler.
#include "main.h"
#include "stm32f0xx_conf.h"
uint32_t TickValue=0;
void TimingDelay_Decrement(void)
{
TickValue--;
}
//------------------------------------------------------------------------------
// Function Name : delay_ms
// Description : delay for some time in ms unit(accurate)
// Input : n_ms is how many ms of time to delay
//------------------------------------------------------------------------------
void delay_ms(uint32_t n_ms)
{
// SysTick interrupt each 1000 Hz with HCLK equal to 32MHz
// - 30 to compensate the overhead of this sub routine
SysTick_Config(8000*PLL_MUL_X - 30);
// Enable the SysTick Counter
TickValue = n_ms;
while(TickValue == n_ms)
;
// SysTick interrupt each 1000 Hz with HCLK equal to 32MHz
SysTick_Config(8000*PLL_MUL_X);
while(TickValue != 0)
;
}
void initgpio()
{
GPIO_InitTypeDef GPIO_InitStructure;
RCC_AHBPeriphClockCmd(RCC_AHBPeriph_GPIOA | RCC_AHBPeriph_GPIOB
| RCC_AHBPeriph_GPIOC, ENABLE);
GPIO_InitStructure.GPIO_Pin = GPIO_Pin_0 | GPIO_Pin_1 |
GPIO_Pin_2 | GPIO_Pin_3 | GPIO_Pin_5 ;
GPIO_InitStructure.GPIO_Speed = GPIO_Speed_10MHz;
GPIO_InitStructure.GPIO_Mode = GPIO_Mode_OUT;
GPIO_InitStructure.GPIO_OType = GPIO_OType_PP;
GPIO_Init(GPIOC, &GPIO_InitStructure);
GPIO_InitStructure.GPIO_Pin = GPIO_Pin_0 | GPIO_Pin_1 ;
GPIO_InitStructure.GPIO_Speed = GPIO_Speed_10MHz;
GPIO_InitStructure.GPIO_Mode = GPIO_Mode_OUT;
GPIO_InitStructure.GPIO_OType = GPIO_OType_PP;
GPIO_Init(GPIOB, &GPIO_InitStructure);
GPIO_InitStructure.GPIO_Pin = GPIO_Pin_0
| GPIO_Pin_1 | GPIO_Pin_2 | GPIO_Pin_3 ;
GPIO_InitStructure.GPIO_Speed = GPIO_Speed_10MHz;
GPIO_InitStructure.GPIO_Mode = GPIO_Mode_OUT;
GPIO_InitStructure.GPIO_OType = GPIO_OType_PP;
GPIO_Init(GPIOA, &GPIO_InitStructure);
GPIO_InitStructure.GPIO_Pin = GPIO_Pin_2 | GPIO_Pin_10 |
GPIO_Pin_11 | GPIO_Pin_12;
GPIO_InitStructure.GPIO_Speed = GPIO_Speed_10MHz;
GPIO_InitStructure.GPIO_Mode = GPIO_Mode_IN;
GPIO_InitStructure.GPIO_OType = GPIO_OType_PP;
GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_DOWN;
GPIO_Init(GPIOB, &GPIO_InitStructure);
}
void display(int b)
{
switch(b)
{
case 0: GPIOA->ODR = 0x0007; //0
GPIOC->ODR = 0x0007;
delay_ms(1000);
break;
case 1:
GPIOA->ODR = 0x0001; //1
GPIOC->ODR = 0x0004;
delay_ms(1000);
break;
case 2:
GPIOA->ODR = 0x000B; //2
GPIOC->ODR = 0x0003;
delay_ms(1000);
break;
case 3:
GPIOA->ODR = 0x000B; //3
GPIOC->ODR = 0x0006;
delay_ms(1000);
break;
case 4:
GPIOA->ODR = 0x000D; //4
GPIOC->ODR = 0x0004;
delay_ms(1000);
break;
case 5:
GPIOA->ODR = 0x000E; //5
GPIOC->ODR = 0x0006;
delay_ms(1000);
break;
case 6:
GPIOA->ODR = 0x000E; //6
GPIOC->ODR = 0x0007;
delay_ms(1000);
break;
case 7:
GPIOA->ODR = 0x0003; //7
GPIOC->ODR = 0x0004;
delay_ms(1000);
break;
case 8:
GPIOA->ODR = 0x000F; //8
GPIOC->ODR = 0x0007;
delay_ms(1000);
break;
case 9:
GPIOA->ODR = 0x000F; //9
GPIOC->ODR = 0x0006;
delay_ms(1000);
break;
case 10:
GPIOA->ODR = 0x000F; //*
GPIOC->ODR = 0x0000;
delay_ms(1000);
break;
case 11:
GPIOA->ODR = 0x0008; //#
GPIOC->ODR = 0x000F;
delay_ms(1000);
break;
}
return ;
}
int main(void)
{
initgpio();
while(1)
{
GPIOC->BSRR = GPIO_Pin_5;//set bit as high
GPIOB->BRR = GPIO_Pin_0;//set bit as low
GPIOB->BRR = GPIO_Pin_1;//set bit as low
{
if(GPIO_ReadInputDataBit(GPIOB, GPIO_Pin_12))//read input
bit PB12
display(3);
if(GPIO_ReadInputDataBit(GPIOB, GPIO_Pin_11)) //read input
bit PB11
display(6);
if(GPIO_ReadInputDataBit(GPIOB, GPIO_Pin_10)) //read input
bit PB10
display(9);
if(GPIO_ReadInputDataBit(GPIOB, GPIO_Pin_2)) //read input
bit PB2
display(11);
}
GPIOC->BRR = GPIO_Pin_5;//set bit as low
GPIOB->BSRR = GPIO_Pin_0;//set bit as high
GPIOB->BRR = GPIO_Pin_1;//set bit as low
{
if(GPIO_ReadInputDataBit(GPIOB, GPIO_Pin_12))
display(2);
if(GPIO_ReadInputDataBit(GPIOB, GPIO_Pin_11))
display(5);
if(GPIO_ReadInputDataBit(GPIOB, GPIO_Pin_10))
display(8);
if(GPIO_ReadInputDataBit(GPIOB, GPIO_Pin_2))
display(0);
}
GPIOC->BRR = GPIO_Pin_5;//set bit as low
GPIOB->BRR = GPIO_Pin_0;//set bit as low
GPIOB->BSRR = GPIO_Pin_1;//set bit ashigh
{
if(GPIO_ReadInputDataBit(GPIOB, GPIO_Pin_12))
display(1);
if(GPIO_ReadInputDataBit(GPIOB, GPIO_Pin_11))
display(4);
if(GPIO_ReadInputDataBit(GPIOB, GPIO_Pin_10))
display(7);
if(GPIO_ReadInputDataBit(GPIOB, GPIO_Pin_2))
display(10);
}
}
}
Click below to visit next and other embedded system
course modules
Module 7: Serial communication
concepts -1
Module 8: RS-232 Basics
Module 9: Controller Area Networking
(CAN)
Module 10: LIN
Module 11: I2C Bus Interface
Module 12: SPI Bus Interface
Module14: USB Interface
Module15: SRAM memory interface
Module16: Flash memory interface
Module17: LCD display panel interface
Module18: Touch pane interface
Module19: Audio/video interface
Previous Modules
Module 1: Introduction
to Embedded Systems: Definition, application and future.
Module 2: Microprocessor, Microcontroller,
MCU Manufacturers, introduction to programming.
Module 3a: Installation of ARM Cortex M0 based LPCXpresso
kit from NXP and sample code
Module 4a: Sample program
for LPCXpresso
Module 3b: Installation of ARM Cortex M0 based STM32F0
Discovery kit from ST Microelectronics and sample code
Module 4b: Sample program for STM32F0 Discovery
Module 5b: ARM Cotex M0
Architecture
