Pi3基础学习套件 Lesson13：IIC 1602液晶

概述

在本课中，我们将学习如何驱动IIC接口的1602液晶显示器

所用器件

1 * Raspberry Pi
1 * Breadboard
1 * IIC 1602
Several jumper wires

工作原理

1602液晶屏能够显示2行，每行16个字符，1602因此而得名。通常1602是并行接口，为了节约GPIO资源，我们对1602屏进行了改造，在1602屏加了一个并行转串行模块PCF8574，这个模块将并行接口改成串行的IIC接口，这样驱动1602屏就只需要2个GPIO口，大大节约了GPIO资源，是Raspberry Pi能挂接更多传感器。

将IIC 1602 LCD接到pi的IIC1上，如图

实物接线

没画

软件

因为需要用到Pi的IIC接口，所以首先应该打开IIC接口，具体操作情况下面

sudo  nano  /boot/config.txt

打开 /boot/config.txt文件后，找到dtparam=i2c_arm，检查dtparam=i2c_arm前是否有#，如果有#将其去掉；再检查dtparam=i2c_arm后面是on还是off，如果是off，需要将off改成on

修改完成后按键盘上的Ctrl+X，按照提示输入Y，保存退出，重启Pi使修改生效。

for  C language user

1) 在/home/pi下新建一个文件，文件名随意（你爱咋咋地）

cd  ~

sudo  nano  i2c1602_lcd.c

向新建的文件中键入如下代码

#include <stdio.h>
#include <wiringPi.h>
#include <wiringPiI2C.h>
#include <string.h>

int LCDAddr = 0x3f;//IIc LCD address
int BLEN = 0;//1--open backlight.0--close backlight
int fd;//linux file descriptor

//writ a word(16 bits) to LCD
void write_word(int data){
    int temp = data;
    if ( BLEN == 1 )
        temp |= 0x08;
    else
        temp &= 0xF7;
    wiringPiI2CWrite(fd, temp);
}

//send command to lcd
void send_command(int comm){
    int buf;
    // Send bit7-4 firstly
    buf = comm & 0xF0;
    buf |= 0x04;            // RS = 0, RW = 0, EN = 1
    write_word(buf);
    delay(2);
    buf &= 0xFB;            // Make EN = 0
    write_word(buf);

    // Send bit3-0 secondly
    buf = (comm & 0x0F) << 4;
    buf |= 0x04;            // RS = 0, RW = 0, EN = 1
    write_word(buf);
    delay(2);
    buf &= 0xFB;            // Make EN = 0
    write_word(buf);
}

//send data to lcd
void send_data(int data){
    int buf;
    // Send bit7-4 firstly
    buf = data & 0xF0;
    buf |= 0x05;            // RS = 1, RW = 0, EN = 1
    write_word(buf);
    delay(2);
    buf &= 0xFB;            // Make EN = 0
    write_word(buf);

    // Send bit3-0 secondly
    buf = (data & 0x0F) << 4;
    buf |= 0x05;            // RS = 1, RW = 0, EN = 1
    write_word(buf);
    delay(2);
    buf &= 0xFB;            // Make EN = 0
    write_word(buf);
}

//initialize the lcd
void init(){
    send_command(0x33); // Must initialize to 8-line mode at first
    delay(5);
    send_command(0x32); // Then initialize to 4-line mode
    delay(5);
    send_command(0x28); // 2 Lines & 5*7 dots
    delay(5);
    send_command(0x0C); // Enable display without cursor
    delay(5);
    send_command(0x01); // Clear Screen
    wiringPiI2CWrite(fd, 0x08);
}

//clear screen
void clear(){
    send_command(0x01); //clear Screen
}

//Print the message on the lcd
void write(int x, int y, char data[]){
    int addr, i;
    int tmp;
    if (x < 0)  x = 0;
    if (x > 15) x = 15;
    if (y < 0)  y = 0;
    if (y > 1)  y = 1;

    // Move cursor
    addr = 0x80 + 0x40 * y + x;
    send_command(addr);
    
    tmp = strlen(data);
    for (i = 0; i < tmp; i++){
        send_data(data[i]);
    }
}

void print_info()
{
    printf("\n");
    printf("|***************************|\n");
    printf("|    IIC 1602 LCD test      |\n");
    printf("| --------------------------|\n");
    printf("| | LCD |            | Pi   |\n");
    printf("| --------------------------|\n");
    printf("| | GND | connect to | GND  |\n");
    printf("| | VCC | connect to | 5V   |\n");
    printf("| | SDA | connect to | SDA.1|\n");
    printf("| | SCL | connect to | SCL.1|\n");
    printf("| --------------------------|\n");
    printf("|                     OSOYOO|\n");
    printf("|***************************|\n");
    printf("Program is running...\n");
    printf("Press Ctrl+C to end the program\n");
}
int main(){
    //init I2C 
    fd = wiringPiI2CSetup(LCDAddr);
    init();
    print_info();
    write(0, 0, "Hi man.Welcome ");
    write(0, 1, "to osoyoo.com");
    delay(3000);
    clear();
    while(1){
        write(0,0,"This is Lesson13");
        write(0,1,"IIC LCD Test");
        delay(1000);
    }
    return 0;
}

保存退出。完整的源代码，可以通过命令wget http://osoyoo.com/driver/pi3_start_learning_kit_lesson_13/i2c1602_lcd.c 下载

3) 编译

gcc   -Wall   -o  i2c1602_lcd   i2c1602_lcd.c    -lwiringPi

4) 执行程序

sudo  ./i2c1602_lcd

5) 最终结果

运行上面的程序，终端会输出1602液晶与pi的连接信息和其他提示信息。同时，在1602液晶上会打印出一些信息。

注意：如果液晶显示太暗，可以通过调节1602背部的可调电位器改变亮度。

for python user

1) 加载模块

sudo nano /etc/modules

打开/etc/modules后，在文件的最后添加上如下两句代码

i2c-bcm2708
i2c-dev

添加完成后，键盘输入Ctrl+X，输入Y保存退出

2) 安装 i2c python library和smbus

sudo apt-get install -y python-smbus i2c-tools

重启Pi

reboot

3) 检查库是否安装成功

lsmod | grep i2c

如果输出类似与图示信息，说明安装成功

如果没有输出类似信息，请重复上述步骤。

4) 测试硬件

sudo i2cdetect -y 1
or
sudo i2cdetect -y 0

根据Pi版本不同，选择其一执行。执行上面的命令后会打印出IIC设备的地址，如图所示

图中的3f(16进制)就是IIC 1602液晶的地址。

5) 编写python脚本控制IIC 1602

A.在/home/pi下新建一个.py脚本文件，文件名随意（你爱咋咋地）

cd  ~

sudo  nano  i2c1602_lcd.py

B.向新建的文件中写入如下代码

import smbus
import time

# Define some device parameters
I2C_ADDR  = 0x3F # I2C device address, if any error, change this address to 0x27
LCD_WIDTH = 16   # Maximum characters per line

# Define some device constants
LCD_CHR = 1 # Mode - Sending data
LCD_CMD = 0 # Mode - Sending command

LCD_LINE_1 = 0x80 # LCD RAM address for the 1st line
LCD_LINE_2 = 0xC0 # LCD RAM address for the 2nd line
LCD_LINE_3 = 0x94 # LCD RAM address for the 3rd line
LCD_LINE_4 = 0xD4 # LCD RAM address for the 4th line

LCD_BACKLIGHT  = 0x08  # On
#LCD_BACKLIGHT = 0x00  # Off

ENABLE = 0b00000100 # Enable bit

# Timing constants
E_PULSE = 0.0005
E_DELAY = 0.0005

#Open I2C interface
#bus = smbus.SMBus(0)  # Rev 1 Pi uses 0
bus = smbus.SMBus(1) # Rev 2 Pi uses 1

def lcd_init():
  # Initialise display
  lcd_byte(0x33,LCD_CMD) # 110011 Initialise
  lcd_byte(0x32,LCD_CMD) # 110010 Initialise
  lcd_byte(0x06,LCD_CMD) # 000110 Cursor move direction
  lcd_byte(0x0C,LCD_CMD) # 001100 Display On,Cursor Off, Blink Off 
  lcd_byte(0x28,LCD_CMD) # 101000 Data length, number of lines, font size
  lcd_byte(0x01,LCD_CMD) # 000001 Clear display
  time.sleep(E_DELAY)

def lcd_byte(bits, mode):
  # Send byte to data pins
  # bits = the data
  # mode = 1 for data
  #        0 for command

  bits_high = mode | (bits & 0xF0) | LCD_BACKLIGHT
  bits_low = mode | ((bits<<4) & 0xF0) | LCD_BACKLIGHT

  # High bits
  bus.write_byte(I2C_ADDR, bits_high)
  lcd_toggle_enable(bits_high)

  # Low bits
  bus.write_byte(I2C_ADDR, bits_low)
  lcd_toggle_enable(bits_low)

def lcd_toggle_enable(bits):
  # Toggle enable
  time.sleep(E_DELAY)
  bus.write_byte(I2C_ADDR, (bits | ENABLE))
  time.sleep(E_PULSE)
  bus.write_byte(I2C_ADDR,(bits & ~ENABLE))
  time.sleep(E_DELAY)

def lcd_string(message,line):
  # Send string to display

  message = message.ljust(LCD_WIDTH," ")

  lcd_byte(line, LCD_CMD)

  for i in range(LCD_WIDTH):
    lcd_byte(ord(message[i]),LCD_CHR)

def main():
  # Main program block

  # Initialise display
  lcd_init()

  while True:

    # Send some test
    lcd_string("Created by         <",LCD_LINE_1)
    lcd_string("Osoyoo.com        <",LCD_LINE_2)

    time.sleep(3)
  
    # Send some more text
    lcd_string("> Tutorial Url:",LCD_LINE_1)
    lcd_string("> https://osoyoo.com",LCD_LINE_2)

    time.sleep(3)

if __name__ == '__main__':

  try:
    main()
  except KeyboardInterrupt:
    pass
  finally:
    lcd_byte(0x01, LCD_CMD)

保存退出。完整代码可以通过下面命令获取
wget http://osoyoo.com/driver/pi3_start_learning_kit_lesson_13/i2c1602_lcd.py

C.执行脚本

sudo  python  ./i2c1602_lcd.py

D.最终结果

运行上面的脚本，1602液晶上会打印出信息。

注意：如果液晶显示太暗，可以通过调节1602背部的可调电位器改变亮度。