Arduino通过I2C(PCF8574T)驱动1602LCD

Arduino中使用I2C通信可直接调用Wire.h库, 这个库允许Arduino链接其他I2C设备, 链接线有两条, 分别是SDA(数据行)和SCI(时钟线). 各型号Arduino的I2C对应引脚:
Arduino Board：I2C / TWI pins
Arduino Uno/Ethernet：A4 (SDA), A5 (SCL)
Arduino Mega2560：20 (SDA), 21 (SCL)
Arduino Leonardo：2 (SDA), 3 (SCL)
Arduino Due：20 (SDA), 21 (SCL), SDA1, SCL1

一般购买到的是分开的两个组件, 需要按下图这样将PCF8574T焊接到1602LCD上

PCF8574T模块4pin(Gnd, Vcc, SDA i2c数据, SCL i2c时钟)和Arduino接口的对应关系: Gnd -> Gnd, Vcc -> Vcc, SDA -> A4, SDL -> A5

获取I2C地址

#include <Wire.h> 

void setup() {
    Serial.begin (115200); // Leonardo: wait for serial port to connect 
    while (!Serial) { } 
    Serial.println (); 
    Serial.println ("I2C scanner. Scanning ..."); 
    byte count = 0; 
    Wire.begin(); 
    for (byte i = 8; i < 120; i++) {
        Wire.beginTransmission (i);
        if (Wire.endTransmission () == 0) {
            Serial.print ("Found address: ");
            Serial.print (i, DEC); Serial.print (" (0x");
            Serial.print (i, HEX); Serial.println (")");
            count++; delay (1); // maybe unneeded?
        } // end of good response
    } // end of for loop 
    Serial.println ("Done."); 
    Serial.print ("Found "); 
    Serial.print (count, DEC); 
    Serial.println (" device(s)."); 
} // end of setup 

void loop() {}

运行时, 打开Serial Monitor, 将波特率设为115200, 看到的输出就是I2C地址

自带LiquidCrystal_I2C显示测试

在运行显示测试前检查是否已经安装了library: LiquidCrystal, LiquidCrystal_I2C

#include <Wire.h>
#include <LiquidCrystal_I2C.h>

// I2C地址, 一般为0x3F, 0x20或0x27
LiquidCrystal_I2C lcd(0x27,16,2);

void setup() {
  lcd.init();
  lcd.backlight(); // 打开背光
}

void loop() {
  lcd.setCursor(0,0);
  lcd.print("LCD1602 iic Test");
  lcd.setCursor(0,1);
  lcd.print("0123456789ABCDEF");
  delay(1000);
}

如果屏幕亮但是无显示, 可以调节背后的电位器让字符显示到合适的对比度.

第三方New LiquidCrystal显示测试

到 https://bitbucket.org/fmalpartida/new-liquidcrystal/downloads/ 下载最新的library并安装

#include <Wire.h>
#include <LCD.h>
#include <LiquidCrystal_I2C.h>
LiquidCrystal_I2C lcd(0x27,2,1,0,4,5,6,7); // 0x27 is the I2C bus address for an unmodified backpack

void setup() { // activate LCD module
    lcd.begin (16,2); // for 16 x 2 LCD module
    lcd.setBacklightPin(3,POSITIVE);
    lcd.setBacklight(HIGH);
}

void loop() {
    lcd.home (); // set cursor to 0,0 
    lcd.print("HELLO WORLD....");
    lcd.setCursor (0,1); // go to start of 2nd line 
    lcd.print(millis());
    delay(1000);
    lcd.setBacklight(LOW); // Backlight off 
    delay(1000);
    lcd.setBacklight(HIGH); // Backlight on 
}

供电和耗电测试

硬件是Arduino NANO + 扩展板 + PCF8574T + 1602LCD, 使用输入电压12V. 扩展板本身不带IC, 只有一个电源LED, 功耗可以忽略. 在使用自带的LiquidCrystal_I2C库跑上面的测试代码时, 测得的功耗仅为0.95W左右.