I'm trying to design a relatively high accuracy auto ranging Ohmmeter. A typical Arduino example can be found here:
The problem with this design is that it uses Diodes to prevent reverse currents. Now to ensure accuracy the exact Diode drop of each and every Diode needs to be known. Initially I thought I could order a "high tolerance Diode" like you can resistors (0.1% etc) but apparently there is no way to guarantee a diode drop.
My next bright idea was to replace all diodes with an 8 channel multiplexer. I had assumed that the "switch" in the multiplexer had an independent resistance but soon found that the On resistance(Ron) of a multiplexer is dependent on the input voltage of the channel selected. Due to the fact that the circuit is used as a voltage divider and there will always be an unknown resistance, the input voltage to each channel will never be the same and so it seems impossible to know what the Ron would be at any given time.
I'm really hoping someone knows of a simple alternative method/solution? I guess relays are an option but they are bulky and seem like overkill. I'm almost tempted to just use diodes and individually measure the diode drop but that makes reproducibility difficult.