andre_chan

Hello, I need to build moisture meter using dc resistance(1k to 50M 10 to 40% of Moisture). It is difficul to find Max4206(logarithmic amplifier) in my country(Indonesia). I had tried to build using opamp(OP07) and transistor(BC547), but doesn't work.I had tried this circuit(J. B. Calvert), but the output not stable. Some one can help me please!