Why cant I control relay using both light and motionsensor at the same time

Projects General Guidance
1

const int LIGHT_SENSOR_PIN = A0; // Arduino pin connected to light sensor's pin
const int RELAY_PIN = 3; // Arduino pin connected to Relay's pin
const int ANALOG_THRESHOLD = 80;

const int MOTION_SENSOR_PIN = 7;
int motionStateCurrent = LOW; // current state of motion sensor's pin
int motionStatePrevious = LOW; // previous state of motion sensor's pin

// variables will change:
int analogValue;

void setup() {
Serial.begin(9600);
pinMode(MOTION_SENSOR_PIN, INPUT); // set arduino pin to input mode
pinMode(RELAY_PIN, OUTPUT); // set arduino pin to output mode

}

void loop() {
motionStatePrevious = motionStateCurrent; // store old state
motionStateCurrent = digitalRead(MOTION_SENSOR_PIN); // read new state

analogValue = analogRead(LIGHT_SENSOR_PIN); // read the input on analog pin

if(analogValue < ANALOG_THRESHOLD && motionStatePrevious == LOW && motionStateCurrent == HIGH) {
digitalWrite(RELAY_PIN, HIGH); // turn on Relay
Serial.println("Motion detected!");

}else{
digitalWrite(RELAY_PIN, LOW); // turn off Relay
Serial.println("Motion stopped!");
}
}

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Please post your code using code tags as described in How to get the best out of this forum.

3

Welcome to the forum

I don't know what IDE you are using or how you posted the sketch, but all of the Carriage Returns an/or Linefeeds have gone missing

Please format the code so that it is readable and post it using code tags

4

The loop function goes round about a million times a second. If MOTION_SENSOR_PIN goes high your code will make RELAY_PIN high. A millionth of a second later it will go low. A relay cannot respond that fast. Put some serial.prints in your code to see what is happening, study the state change and doing several things at the same time tutorials.

5

What output are you getting now? How is the relay behaving?

6

Analyze this "if":
if (analogValue < ANALOG_THRESHOLD && motionStatePrevious == LOW && motionStateCurrent == HIGH) {

MotionStatePrevious and motionStateCurrent are always in the same condition, either both HIGH or both LOW.

See in the simulator.
In the simulator I added a delay to preview the print.
I used an LDR as a LIGHT sensor and a PIR as a presence sensor.
Adjust LDR for more 3,500 LUX and simulate motion on PIR

7

Are you sure? Maybe I am misreading, but as I see it if MOTION_SENSOR_PIN goes high then motionStateCurrent will also go high but motionStatePrevious will remain low until the next iteration of the loop function, giving the possibility of the if statement being true for one iteration of the loop function, assuming that analogValue is less than ANALOG_THRESHOLD. However, as per my previous reply, this is only the case for about 1 millionth of a second, or however long the loop function takes to go round once.

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8

I think you're right, I'll review it in the simulator.

9

The relay doesn't turn on and in serial monitor it says motion stopped and it doesn't change when I move in front

10

@PerryBebbington is right.
I redid the simulator, I put a delay in the simulator, leaving only the printout of the activated relay.
See again in the simulator above.

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It works now. thank you very much for your help

1 Like
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