Arduino Nano + 1602 LCD 打造高精度时钟：软件校准内部时钟

元器件与材料

• Arduino Nano R3 ×1 (其它 Arduino 也可)
• 1602 字符型 LCD ×1
• 轻触按键 ×3
• 10kΩ 调节电位器 ×1 (调对比度)
• 跳线若干

项目简介

最初是学术练习，最终做出极高精度时钟：连续运行 5 天零误差。

Arduino 内部时钟频率不完全准确，直接用 millis() 计时会累积偏差。我的方法：实测单片机每小时快/慢多少毫秒，在代码中每小时修正该偏差。

经 5 天验证，内部时钟偏差稳定一致，软件修正有效。

第二问题：millis() 约 50 天溢出且不可修改。解法：重写 Timer0 中断，自维护毫秒计数器，午夜归零，彻底规避溢出。

测量单片机偏差

假设电脑时钟准确。写 Arduino 程序每 2 秒发送毫秒数给 Processing，Processing 对比自家 millis()，一小时后得出偏差值，即为时钟代码中的 speedCorrection。

Arduino 测试程序与 Processing 脚本见代码章节。无 Processing 者可至 processing.org 下载。

时钟核心代码解析

自定义毫秒中断

// 占用 Timer0，millis()/delay() 将失效
TCCR0A = (1 << WGM01);           // CTC 模式
OCR0A = 0xF9;                    // 249 -> 1ms @ 16MHz/64
TIMSK0 |= (1 << OCIE0A);         // 开启比较匹配中断
TCCR0B |= (1 << CS01) | (1 << CS00); // 64 分频
TCNT0 = 0;
sei();

中断服务程序 (每毫秒调用)：

volatile unsigned long currentTime = 0; // 午夜起毫秒数
volatile unsigned long elapsed = 0;     // 小时计数器

ISR(TIMER0_COMPA_vect) {
  if (currentMode != SET_TIME) currentTime++;
  elapsed++;
}

变量加 volatile 防止编译器优化导致读取缓存值。

日期处理：儒略日算法

日期存儒略日数 (自公元前 4713-01-01 起天数)，含互转格里高利历函数：

float JulianDate(int d, int m, int y) {
  if (m < 3) { m += 12; y -= 1; }
  unsigned long t1 = (153 * m - 457) / 5;
  unsigned long t2 = 365 * y + y/4 - y/100 + y/400;
  return 1721118.5 + d + t1 + t2;
}
void GregorianDate(float jd, int &d, int &m, int &y) {
  unsigned long f = jd + 68569.5;
  unsigned long e = (4 * f) / 146097;
  unsigned long g = f - (146097 * e + 3) / 4;
  unsigned long h = 4000 * (g + 1) / 1461001;
  unsigned long t = g - (1461 * h / 4) + 31;
  unsigned long u = (80 * t) / 2447;
  unsigned long v = u / 11;
  y = 100 * (e - 49) + h + v;
  m = u + 2 - 12 * v;
  d = t - 2447 * u / 80;
}

每日归零与每小时修正

const unsigned long MS_DAY = 24UL*60*60*1000;
const unsigned long MS_HOUR = 60UL*60*1000;
int speedCorrection = 3545; // 实测每小时慢 3545ms，快则填负数

void loop() {
  // 跨天处理
  if (currentMode == SHOW_TIME && currentTime > MS_DAY) {
    noInterrupts();
    currentTime -= MS_DAY;
    interrupts();
    currentDate++;
  }
  // 每小时修正
  if (elapsed >= MS_HOUR) {
    noInterrupts();
    currentTime += speedCorrection;
    elapsed = 0;
    interrupts();
  }
  // ... 按键检测、显示更新等
}

修正时关中断防止计数器被 ISR 破坏。

三按键交互

• Mode 键 (D2)：切换 模式：显示 → 设时 → 设年 → 设月日 → 设修正值 → 回显示
• Up/Down 键 (D3/D4)：各模式下增减对应数值
• 设修正值模式下，每按一次调整 5ms

代码

主时钟程序

// Paul Brace - Feb 2021
// 无 RTC 模块的高精度时钟，含软件时钟修正
#include 
LiquidCrystal lcd(12, 13, 6, 7, 8, 9);

#define MODE_BUTTON 2
#define HOUR_BUTTON 3
#define UP_BUTTON 3
#define DAY_BUTTON 3
#define MINUTE_BUTTON 4
#define DOWN_BUTTON 4
#define MONTH_BUTTON 4

#define SHOW_TIME 1
#define SET_TIME 2
#define SET_YEAR 3
#define SET_DATE 4
#define SET_SPEED_ADJ 5

int speedCorrection = 3545; // 根据实测修改
volatile unsigned long currentTime = 0;
unsigned long lastTime = -1000;
volatile unsigned long elapsed = 0;
unsigned long millisecondsInADay = 24UL*60*60*1000;
unsigned long millisecondsInHour = 60UL*60*1000;
int currentMode = SHOW_TIME;
float currentDate = JulianDate(1,1,2021);
float lastDate = 0;
int currentDay, currentMonth, currentYear;
char *dayArray[] = {"Tue. ","Wed. ","Thur. ","Fri. ","Sat. ","Sun. ","Mon. "};

void setup() {
  // Timer0 中断设置 (同上)
  TCCR0A = (1<

Arduino 偏差测试程序

// 每 2 秒发送毫秒数给 Processing
int inByte = 0;
unsigned long firstReading = 100000;

void setup() {
  Serial.begin(9600);
  sayHello();
}

void loop() {
  if (Serial.available() > 0) {
    inByte = Serial.read();
    Serial.print(millis() - firstReading);
    Serial.print('E');
    delay(2000);
  }
}

void sayHello() {
  while (Serial.available() <= 0) {
    Serial.print('Z'); delay(200);
  }
  firstReading = millis();
}

Processing 对比脚本

// Processing 3.x
import processing.serial.*;
Serial theSerialPort;
int[] serialBytesArray = new int[15];
int bytesCount = 0;
boolean init = false;
long mills = 0, first = 0, now, firstReading = 100000, DiffPerHour = 0;

void setup() {
  size(500,500); background(70); noStroke();
  printArray(Serial.list());
  theSerialPort = new Serial(this, Serial.list()[1], 9600);
}

void draw() {
  background(70); fill(255); textSize(25);
  text(hour()+":"+minute()+":"+second(), 50, 50);
  text("Incoming: "+mills, 50, 100);
  text("Local: "+(now-firstReading), 50, 150);
  text("Diff: "+(mills-(now-firstReading)), 50, 200);
  if ((now-firstReading)>=3600000 && DiffPerHour==0)
    DiffPerHour = mills - (now-firstReading);
  text("Diff after 1hr: "+DiffPerHour, 50, 300);
}

void serialEvent(Serial myPort) {
  int inByte = myPort.read();
  if (!init) {
    if (inByte == 'Z') { myPort.clear(); init=true; myPort.write('Z'); if(first==0) first=millis(); }
  } else {
    if (inByte != 69 && bytesCount < 14) {
      serialBytesArray[bytesCount++] = inByte;
    }
    if (inByte == 69) {
      now = millis();
      mills = 0;
      for (int i=1; i<=bytesCount; i++)
        mills += (serialBytesArray[i-1]-48) * pow(10, bytesCount-i);
      if (firstReading == 100000) firstReading = now;
      myPort.write('Z');
      bytesCount = 0;
    }
  }
}

原理图

Arduino Nano 实现 DS3231 RTC 与 GPS 同步精准计时 Arduino UNO 制作高精度电子秤：分步指南、元件清单与代码