so, i need to make a mini project for my college. And i have deicided to make a wood expansion calculator, now the problem is to calculate the expansion in wet woods, i need to find resistance or moisture content in the wood. Though i have decided to find the resistance method. I need help to find to measure the very high resistance(in Gigaohms range) in the wood with the help of arduino. Can someone please guide me with the circuit to calculate the resistance?
"Wet woods" do not have gigaOhm resistances. For a randomly chosen example see Measure the Moisture Content of Your Firewood With a Multimeter : 4 Steps (with Pictures) - Instructables
In any case, measuring resistances in the gigaOhm range is not a project for amateurs, and has nothing to do with Arduino. Circuits designed by professionals are required, as are special material handling techniques.
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I think you area bit confused. Wet wood has lower resistance than dry wood. Use you DVM to test that statement!
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I assume you know Ohm's Law?
A quick search found this.
A regular DMM (digital multi-meter) measures resistance by applying a known-fixed current and measuring voltage.
High resistance is tricky because it takes higher voltage to push current through a high resistance. And we usually want to avoid dangerous voltages. Besides danger to humans, the regular Arduino can't handle more than 5V.
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Check the web site of any of the commercial wood moisture checkers.
Do NOT make the mistake of believing the movie scene where the bad guy is electrocuted by stepping in a puddle of water with a hot wire in it. Pure water is actually an insulator, but even modern tap water is a conductor so your 'wet' wood will depend on the amount of dissolved salts. Now what will you actually be measuring?