How to use DO pin on ldr module? I have ldr module with 4 pins
 1. Vin
 2. Gnd
 3. AO
 4. DO

I want to know how can i take advantage of DO suppose i want to turn on lcd display when light falls on the ldr sensor! 


I have noticed when light falls on ldr sensor the Green  led with DO written next to it lights up.
The DO pin gives a Digital Output that is HIGH when the light falling on the LDR is above a threshold, and LOW when it's below a threshold. Just connect it to a digital input pin and read that pin with digitalRead(). 

You can change the threshold by adjusting the small blue trimpot.