Arduino Motion Sensor Light timer - c++

Question

currently trying to make a motion sensor light that i can turn on and off with sensor detection but also have auto turn off after lets say 15 minutes if left on.
I've got it so i can turn it off and on now using motion but not sure how to have it auto turn off after a set time since delay blocks me from turning it off with motion if i try using that.
I'm thinking I'll have to use the millis function? but not sure where to start and feel like I've hit a wall so any guidance would be appreciated.
here's the code i have so far to have the sensor turn it off and on.
int pir = 2;
int val;
int state = 0;
void setup() {
pinMode(led, OUTPUT);
pinMode(pir, INPUT);
}
void loop() {
val = digitalRead(pir);
if (val == HIGH)
{
if (state == 0)
{
state = 1;
digitalWrite(led, HIGH);
delay (4000);
}
else {
state = 0;
digitalWrite(led, LOW);
delay (4000);
}
}
}```

Answer 1

have a global variable unsigned long sleep_start;. Set sleep_start = 0 everytime you turn the LED off andsleep_start = millis(); every time the LED goes on.
Then at the start of loop():
if (sleep_start > 0 && millis() > sleep_start + 15 * 60 * 1000) {
// it is now over 15 minutes since the LED went on
// do whatever you want - turn LED off and set state = 0 ?
}
I not you have your actions and state tied together - i.e. you set the state and then turn on/off the LED at the same time. Much better to set the state separately and then set the LED based on the state.
void loop()
{
unsigned long now = millis();
val = digitalRead(pir);
bool state_changed = false;
if (val == HIGH)
{
if (state == 0)
state = 1;
else
state = 0;
state_changed = true;
}
// state was not changed by the sensor so look for timeout
if (!state_changed)
{
if (state == 1 && now > sleep_start + 15 * 60 * 1000)
{
state = 0;
state_changed = true;
}
}
if (state_changed)
{
switch(state) {
case 0: digitalWrite(led, LOW);
break;
case 1: digitalWrite(led, HIGH);
sleep_start = now;
break;
}
}
delay(4000);
}