LDR photosensor with arduino

Using Arduino General Electronics
1

I have connected my LDR between A0 and 3volts on my board and a 10k resistor between 3volts and ground, as i have seen on a schematic,
but i only get high values, its giving 1024 even in low light and it only goes down to 600 even if i cover it,
i tried to change the resistor to 3.3k ohms but its still the same.
is there a problem with the sensor or the resistor value?

2

Your schematic is wrong if it shows those connections.

3

Make it look like this:

1029×796 8.55 KB

Then try reversing the positions of the 10K resistor and the LDR. What happens then?

Ron

4

Or for a simple test, connect the LDR from analog input to ground. Set the pinMode of the input to INPUT_PULLUP to enable the internal pullup resistor. Then no external resistor is needed.

example of LDR on input pullup analog input pin:

const byte ldrPin = A0;

void setup()
{
   Serial.begin(115200);
   Serial.println("LDR Test Program");
   pinMode(ldrPin, INPUT_PULLUP);
}

void loop()
{
   static unsigned long timer = 0;
   unsigned long interval = 1000;
   if (millis() - timer >= interval)
   {
      timer = millis();
      int ldrReading = analogRead(ldrPin);
      Serial.print("ldr reading = ");
      Serial.println(ldrReading);
   }
}

Reads low numbers when in light, high when dark. Often when using the internal pullup the sensitivity is OK, but if not then use an external resistor.

5

but i only get high values, its giving 1024 even in low light and it only goes down to 600 even if i cover it,

So you need to drop the value of the resistor in the circuit shown in reply #2.

For best results measure the resistance of the LDR in the mid light level you want and make the resistor as close to this value as you can.

6

szevlin:
I have connected my LDR between A0 and 3volts on my board and a 10k resistor between 3volts and ground, as i have seen on a schematic,
but i only get high values, its giving 1024 even in low light and it only goes down to 600 even if i cover it,
i tried to change the resistor to 3.3k ohms but its still the same.
is there a problem with the sensor or the resistor value?

Try the resistor between A0 and gnd, with the LDR between 3V and A0.
Tom... :slight_smile: