I have been working on a project at my high school dealing with op amps and the theories behind them. The problem that I have come to is that the Arduino can only read voltages with an input impedance of 10kohms or so. This is kind of difficult in my situation because for the first section of my circuit I need to keep the impedance fairly high. So when I try to analogRead() the voltage from the output of the op amp circuit I find that the Arduino spits out random voltages anywhere from 0.30 to 4.9 volts, when the actual voltage is at 2.56 volts. I have found people using capacitors to ground and unity gain amplifiers to remedy the situation, but have found that the unity gain amplifier doesn't seem so solve anything and the capacitor seems like it would not give the most accurate reading for me. Oh, and also I will only need to read the voltage off of this amplifier every 30 seconds to 60 seconds, but I need the solution to this problem be able to accurately provide the correct voltage every time (even at 1/2 second sample times), it has to be exact.
op supply amp voltage +6volts to -6volts op amp output voltage range: 0volts to 5volts (to Arduino)