LDR which resistor

Using Arduino Sensors
1

Hi all.

I am creating an auto lights on unit using an Arduino UNO and a NORPS 12, 13MM diameter LDR. My problem is this i do not know how to work out what size resistor i need, i have looked on the internet for ideas and found many examples, but confusingly a lot of examples show different value resistors ranging for 300R to 100K, How do i work out what i require ?

Regards

Ray

2

How do i work out what i require ?

Use a pot wired as a variable resistor as one leg of the voltage divider with the LDR. Adjust the pot to get the sensitivity that you want. Measure the pot when you have it right and replace the pot with a fixed resistor if you want.

3

Measure the resistance of the LDR with a DMM at the light level you want to use it.
Use about the same value pull up resistor.
That will give you the most A/D value change at that light level.
Leo..

4

Hi.

Many thanks to you both.

Regards

Ray

5