/diy/ - Do It Yourself

Hey guys, I'd like to be able to control pic related with a microcontroller, be able to select which resistor to use for autoranging. I have a current source which I want to measure. The current source can go from low to large currents and when the current is too low, it drops below the adc resolution. So I'd like to be able to switch sensing resistors when that happens automatically. I was thinking of using a transistor to do it, but I think it can cause issues with AC signals since the input is a large signal that can change the biasing of the transistor significantly. Anyone knows how I can accomplish this? Bonus point if your solution allows for more than 2 resistors (like 3-4 resistors). I have a limited amount of ADC channels so using one adc channel per level is not good, I need to be able to measure it all from one adc input.