avoiding immediately turning relay on or off.

Projects General Guidance
1

I have a relay to control the backlight of the lcd using a relay.

    // Turn on LCD backlight when motion detected at night and day.
    digitalWrite(RELAY2, (photoresistorValue >= 700) || pir_sensor_value);

but sometimes

photoresistorValue

is closely shuffling near ± 700 ,
so I want to know a way that of a condition is set to true it should not immidiately turn of relay but wait for a while instead to meet the new condition .

2

Treat the photoresistorValue as a switch and debounce it.

3

Use hysteresis. Turn the backlight on at or greater than 700, but off at, say, 650 or less.

4

groundFungus:
Use hysteresis. Turn the backlight on at or greater than 700, but off at, say, 650 or less.

Agreed, this is how it's done in many products (eg thermostats)

5

Can you please review my code?

int RELAY2 = D4;
int RELAY3 = D5;
int RELAY4 = D6;
int photoresistor = A0;
int pir_sensor_value = 0;
int photoresistorValue = 0;

#define PIR_SENSOR_PIN D7

int backlightState = HIGH ;
int reading = LOW;
int relay2State;
int lastRelay2State = LOW;

unsigned long lastDebounceTime = 0; // the last time the output 
unsigned long debounceDelay = 50; // the debounce time; increase of the output flickers.

void setup() {
    //Initilize the relay control pins as output
    pinMode(RELAY2, OUTPUT);
    pinMode(RELAY3, OUTPUT); // D5
    pinMode(RELAY4, OUTPUT);
    pinMode(photoresistor, INPUT);
    pinMode(PIR_SENSOR_PIN, INPUT);  
}

void loop (){
   if (photoresistorValue >= 700 || pir_sensor_value){
        reading = HIGH;
    }
    else {
        reading = LOW;
    }
    if (reading != lastRelay2State) {
        // reset the debouncing timer
        lastDebounceTime = millis();
    }
    
    if ((millis() - lastDebounceTime) > debounceDelay) {
        // whatever the reading is at, it's been there for longer than the debounce
        // delay, so take it as the actual current state:
    
        // if the button state has changed:
            if (reading != relay2State) {
              relay2State = reading;
        
              // only toggle the LED if the new button state is HIGH
              if (relay2State == HIGH) {
                backlightState = !backlightState;
              }
            }
        }
    // Set the backlight of lcd
    digitalWrite(RELAY2, backlightState);
}
6

Well, it doesn't compile, so not really.

7

seaurchin:
Can you please review my code?

please share the whole sketch, and add descriptions/comments where neccesairy

8

Now it shoudld work I have udpated my code, the debounce doesnt seem to be working correctly the backlight stays on forever.