除了LED之外，液晶也是ARDUIN经常使用的显示器材。本节我们介绍常用的1602液晶显示的使用：  对应的硬件原理图  虽然液晶显示比LED更复杂，但是由于内部都有显示控制芯片所以反而使用起来比LED更简单（当然，也有LED控制芯片，如果不怕增加成本使用这样的芯片，这样arduino和LED的编程也可以简单了）。由于使用了arduino液晶显示库，所以液晶控制部分比较简单。我们平时也可以参考硬件设计，就是将液晶的数字和控制端依次由arduino数字管脚连接，然后将这些管脚的数字编号在初始化部分赋值给控制库程序。就这样，我们就可以在主程序中调用各种显示指令了。不很难的，试一下就知道！ ``` /* LiquidCrystal Library - Hello World Demonstrates the use a 16x2 LCD display. The LiquidCrystal library works with all LCD displays that are compatible with the Hitachi HD44780 driver. There are many of them out there, and you can usually tell them by the 16-pin interface. This sketch prints "Hello World!" to the LCD and shows the time. The circuit: * LCD RS pin to digital pin 12 * LCD Enable pin to digital pin 11 * LCD D4 pin to digital pin 5 * LCD D5 pin to digital pin 4 * LCD D6 pin to digital pin 3 * LCD D7 pin to digital pin 2 * LCD R/W pin to ground * LCD VSS pin to ground * LCD VCC pin to 5V * 10K resistor: * ends to +5V and ground * wiper to LCD VO pin (pin 3) Library originally added 18 Apr 2008 by David A. Mellis library modified 5 Jul 2009 by Limor Fried (http://www.ladyada.net) example added 9 Jul 2009 by Tom Igoe modified 22 Nov 2010 by Tom Igoe This example code is in the public domain. http://www.arduino.cc/en/Tutorial/LiquidCrystal */ // include the library code: #include <LiquidCrystal.h> // initialize the library with the numbers of the interface pins LiquidCrystal lcd(12, 11, 5, 4, 3, 2); void setup() { // set up the LCD's number of columns and rows: lcd.begin(16, 2); // Print a message to the LCD. lcd.print("hello, world!"); } void loop() { // set the cursor to column 0, line 1 // (note: line 1 is the second row, since counting begins with 0): lcd.setCursor(0, 1); // print the number of seconds since reset: lcd.print(millis() / 1000); } ``` 综合范例小游戏，用户通过拨码开关给出对应的数字的二进制换算结果，每次由程序给出随机的数字让用户换算。学习ARDUINO外部中断的使用，巩固以前的硬件知识。  ``` // include the library code: #include <LiquidCrystal.h> // initialize the library with the numbers of the interface pins LiquidCrystal lcd(7, 8, 9, 10, 11, 12); const int Pin0 = 6; // Binary number 2^1 or 1 const int Pin1 = 5; // Binary number 2^2 or 2 const int Pin2 = 4; // Binary number 2^3 or 4 const int Pin3 = 3; // Binary number 2^4 or 8 const int Pin4 = A4; // Binary number 2^5 or 16 const int Pin5 = A3; // Binary number 2^6 or 32 const int Pin6 = A2; // Binary number 2^7 or 64 const int Pin7 = A1; // Binary number 2^8 or 128 const int easyMode = A0; // Easy mode is 0-15, Hard is 0-255 int BinaryValue; // Value for adding up numbers to compare to random number int correctNumber = 0; // Flag to see if the number was correct int wrongNumber = 0; // Flag to see if the number was wrong const int buzzer = 13; //Buzzer pin int freq; //frequency out const int buttonPin = 2; // the number of the pushbutton pin int buttonState; // variable for reading the pushbutton status long randNumber; // variable for the random number void setup() { lcd.begin(16, 2); // set up the LCD's number of columns and rows pinMode(Pin0, INPUT_PULLUP); pinMode(Pin1, INPUT_PULLUP); pinMode(Pin2, INPUT_PULLUP); pinMode(Pin3, INPUT_PULLUP); pinMode(Pin4, INPUT_PULLUP); pinMode(Pin5, INPUT_PULLUP); pinMode(Pin6, INPUT_PULLUP); pinMode(Pin7, INPUT_PULLUP); pinMode(easyMode, INPUT_PULLUP); pinMode(buttonPin, INPUT_PULLUP); pinMode(buzzer, OUTPUT); // Set buzzer pin as OUTPUT // if analog input pin 5 is unconnected, random analog // noise will cause the call to randomSeed() to generate // different seed numbers each time the sketch runs. // randomSeed() will then shuffle the random function. randomSeed(analogRead(5)); if (digitalRead(easyMode) == HIGH) { randNumber = random(0, 15); } else { randNumber = random(0, 255); } // Print a message to the LCD. lcd.print("Your number is"); // set the cursor to column 0, line 1 // (note: line 1 is the second row, since counting begins with 0): lcd.setCursor(0, 1); lcd.print(randNumber); // Print the random number } void checkNumber() // Check switches for correct number { if (digitalRead(Pin0) == HIGH) { BinaryValue = 1; } else { BinaryValue = 0; } if (digitalRead(Pin1) == HIGH) { BinaryValue = BinaryValue + 2; } if (digitalRead(Pin2) == HIGH) { BinaryValue = BinaryValue + 4; } if (digitalRead(Pin3) == HIGH) { BinaryValue = BinaryValue + 8; } if (digitalRead(Pin4) == HIGH) { BinaryValue = BinaryValue + 16; } if (digitalRead(Pin5) == HIGH) { BinaryValue = BinaryValue + 32; } if (digitalRead(Pin6) == HIGH) { BinaryValue = BinaryValue + 64; } if (digitalRead(Pin7) == HIGH) { BinaryValue = BinaryValue + 128; } if (BinaryValue == randNumber) // Check if switches match random number { correctNumber = 1; } else { wrongNumber = 1; } } void printBinary() // Displays status of switches { if (digitalRead(Pin7) == LOW) { lcd.print("0"); } else { lcd.print("1"); } if (digitalRead(Pin6) == LOW) { lcd.print("0"); } else { lcd.print("1"); } if (digitalRead(Pin5) == LOW) { lcd.print("0"); } else { lcd.print("1"); } if (digitalRead(Pin4) == LOW) { lcd.print("0"); } else { lcd.print("1"); } lcd.print(" "); if (digitalRead(Pin3) == LOW) { lcd.print("0"); } else { lcd.print("1"); } if (digitalRead(Pin2) == LOW) { lcd.print("0"); } else { lcd.print("1"); } if (digitalRead(Pin1) == LOW) { lcd.print("0"); } else { lcd.print("1"); } if (digitalRead(Pin0) == LOW) { lcd.print("0"); } else { lcd.print("1"); } } void loop() { attachInterrupt(digitalPinToInterrupt(buttonPin), checkNumber, FALLING); // Wait for pushbutton to be pressed, when pressed check to see if correct number is inputted lcd.setCursor(7, 1); printBinary(); // Display status of switches if (wrongNumber == 1) { lcd.clear(); lcd.setCursor(0, 0); lcd.print("Try again"); lcd.setCursor(0, 1); lcd.print(randNumber); tone(buzzer, 200); // Play wrong answer tone delay(400); noTone(buzzer); // Stop sound... wrongNumber = 0; correctNumber = 0; } if (correctNumber == 1) { tone(buzzer, 600); // Play correct answer tone delay(100); tone(buzzer, 1000); delay(100); tone(buzzer, 800); delay(100); noTone(buzzer); // Stop sound... lcd.clear(); lcd.setCursor(0, 0); lcd.print("Correct!"); lcd.setCursor(0, 1); lcd.print(randNumber); lcd.print(" is "); printBinary(); // Display status of switches delay(3000); lcd.clear(); lcd.setCursor(0, 0); // Print a message to the LCD. lcd.print("Your number is"); // set the cursor to column 0, line 1 // (note: line 1 is the second row, since counting begins with 0): lcd.setCursor(0, 1); if (digitalRead(easyMode) == HIGH) { randNumber = random(0, 15); } else { randNumber = random(0, 255); } lcd.print(randNumber); correctNumber = 0; wrongNumber = 0; } } ```