c - 如何延迟关闭继电器(毫秒)

当我按下按钮（U），然后将其关闭时，我试图打开继电器5秒钟。然后打开第二个继电器10秒钟并关闭它。我想使用毫秒功能在不同的时间间隔控制8个继电器。
请更正我的代码。

为什么不起作用？
（带一个继电器的代码）

#include <LiquidCrystal.h>
LiquidCrystal lcd(8, 9, 4, 5, 6, 7);

int ssr1 = 2;
int ssr2 = 3;

int lcd_key     = 0;
int adc_key_in  = 0;

#define R   0
#define U   1
#define D   2
#define L   3
#define S   4
#define N   5

unsigned long interval = 5000;
unsigned long previousMillis = 0;

int read_LCD_buttons(){
adc_key_in = analogRead(0);

if (adc_key_in > 1000) return N;
if (adc_key_in < 50)   return R;
if (adc_key_in < 250)  return U;
if (adc_key_in < 450)  return D;
if (adc_key_in < 650)  return L;
if (adc_key_in < 850)  return S;

return N;
}
   void setup(){
   lcd.begin(16, 2);
   lcd.setCursor(0,0);
   lcd.print("Select:");
   pinMode(3, OUTPUT);
}

void loop(){

   unsigned long currentMillis = millis();

   lcd.setCursor(0,1);
   lcd_key = read_LCD_buttons();

   switch (lcd_key){

       case U:{
           digitalWrite(3, HIGH);
           if ((unsigned long)(currentMillis - previousMillis) >= interval){
           digitalWrite(3, LOW);
           previousMillis = millis();
           }
           lcd.print("START");
           break;
       }
       case D:{
             digitalWrite(3, LOW);
             lcd.print("STOP");
             break;
      }
      case N:{
             break;
      }
  }
}

最佳答案

我建议您查看各种Arduino教程。
但是，根据您的要求，我在下面提供了示例代码。
请注意，这尚未经过测试。但是，您应该了解逻辑并进行相应调整。
还有许多其他方法可以达到相同的结果。

int relayState = RELAY_STATE_OFF; // track state of the relay
unsigned long relayOnAt = 0; // time at which relay was turned ON

void relay(int turnOn)
{
  if( turnOn == ON ) digitalWrite(3,HIGH);
  else digitalWrite(3,LOW);
}

void processRelay(int operateRelay)
{
  switch(relayState){
    case RELAY_STATE_OFF:
           if( operateRelay == 1) {
             relay(ON);
             relayState = RELAY_STATE_ON;
             relayOnAt = millis(); // remember when the relay was turned on
           }
           break;
    case RELAY_STATE_ON: // wait here for interval seconds to elapse
          if( millis() - relayOnAt >= interval) {
            relay(OFF);
            relayState = RELAY_STATE_OFF; // go back to checking key input
          }
          break;
    default:
        relayState = RELAY_STATE_OFF;
        break;
  }
}

int operateRelay = 0;
void loop(){
   lcd.setCursor(0,1);
   lcd_key = read_LCD_buttons();

   operateRelay = 0;
   if( lcd_key == U ) {
     operateRelay = 1;
   }
   processRelay(operateRelay);

}