Calculate divider calculation

Hi!

I want to use an LDR to get a reading on the PIC via A2D converter. Here are my measured resistance levels of the LDR:

Dark: 65K Ohm
Normal light: 3.98K
Very bright: 1.8K

If I want to get a voltage range of 0V through to 5V to the PIC from the LDR, I know I need a voltage divider circuit, but how do I work out the resistance of the static resistor, and is there an online calculator to simply this?

Ive looked but I couldnt find what I needed,

James

First, without using an opamp, starting with only a single supply voltage of 5V?, there is no way to get a signal that swings from 0V to 5V. You could get maybe 1.5V to 3.5V. Is that enough?

What supply voltages do you have to work with?

Hi Mike.

15V comes onto the board, which is stepped down to 12V, then 5v. It would be the easiest to use the 5V line.

I think a swing from 1.5V to 3.5V would be fine.

You won't be able to get 0 to 5 volts but you can center it with a couple of calculations. Try 11k.

11K looks like it will give me a range of 4.29V to 0.72V which is pretty good, with a 5V input voltage. Thank you