How to delay switching off the relay (millis) - c

Question

I'm trying to turn on the relay for 5s when I press the button(U), then turn it off. Then switch on the second one for 10 seconds and turn it off.I would like to use the millis function to control 8 relays at different time intervals.
Please correct my code.
Why doesn't it work?
(code with one relay)
#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;
}
}
}

Answer 1

I suggest you check out various Arduino tutorials.
However, based on your request, I have included example code below.
Please note that this has not been tested. However, you should get an idea of the logic and adapt accordingly.
There are many other ways to achieve the same result.
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);
}