Theoretical basis for Resistance Measurement with a microcontroller

[Iuri]

I'm thinking in build a Resistance Meter using a microcontroller, but dont know exactly how to do this.

My requirements at beginning: 0 ~ 10Mohms

Searching around, I've found an Microchip application note that describles a construction of a R meter, but the range is too low (0~999ohms) for my desires.

My first thought was to build a 555 in a astable mode, using R1 or R2 as my "unkown" parameter and measuring the frequency given get the resistance associated, but seens to be a worst solution, maybe even not a solution.

Anyone can lead me a way in the resistance measurement? common circuitry, related theory, advices, ...

Thank you!

P.S: not sure if i posted it in the right place

 

[godfreyl]

Does the microcontroller have an analog input? That would make it easier.

 

[Iuri]

Yes, i'm using the PIC 18F2550.

 

[mgate]

You can do it trough a voltage divider... or a Wheatstone bridge ... But I don't know if you can have all that range with a single circuit