How to add a time delay when reading a sensor - arduino - arduino

Question

I am making a project that has to sense ambient light with a LDR. The idea is, that when the value of the LDR is low for 3 seconds, the led turns on. Also when the value of that LDR gets higher again, and stays high for 3 seconds, the led should turn of. This is so I can avoid that just a cloud or somebody waving over the sensor turns the led on immediately.
I know that I can use the mills() function here like in the blink without delay tutorial. But it doesn't seem to work....
this is my code so far:
#define ledPin 2
#define ldrPin A0
int daylight = 430;
int night = 150;
int ledState = 0;
int lightState = 0;
const long timeOut = 2000;
unsigned long previousMillis = 0;
unsigned long previousMillis2 = 0;
unsigned long tNow = 0;
void setup() {
// put your setup code here, to run once:
pinMode(ledPin, OUTPUT);
pinMode(ldrPin, INPUT);
Serial.begin(9600);
}
void loop() {
// put your main code here, to run repeatedly:
tNow = millis();
int value = analogRead(ldrPin);
switch (lightState) {
case 0:
ledState = 0;
if (value <= 200 && (tNow - previousMillis) >= timeOut)
{
previousMillis = tNow;
lightState = 1;
}
break;
case 1:
ledState = 1;
if (value >= 300 && (tNow - previousMillis2) >= timeOut)
{
previousMillis2 = tNow;
lightState = 0;
}
break;
}
switch (ledState) {
case 0:
digitalWrite(ledPin, LOW);
break;
case 1:
digitalWrite(ledPin, HIGH);
break;
}
Serial.println(value);
Serial.println(ledState);
}

Answer 1

You could try using smoothing to read a running average from the sensor. That way you'll have a smoothed average instead of an immediate value, so a short spike (like a hand) won't change the value if you keep the window long enough.
There is a tutorial on the arduino website explaining how to do this. Basically you store multiple previous values and keep track of the average.