I would also like to thank Rerouter for suggesting that Howland current source circuit.
I had been looking for something like that for a while as a solution to a problem I'd been dealing with when using a simple divider circuit to take ADC readings from a specific type of potentiometer that has very poor manufacturing tolerances and varied quite a lot from instance to instance. The knob on this pot has several detent positions, and I was trying to come up with a universal set of threshold values to determine position, but failing due to the aforementioned variation.
I tried this circuit out yesterday (using an MCP602) and it works rather nicely, giving me a linear voltage output with wide steps between pot positions.
But, I have a question: my pots are 45-50K, so through trial-and-error in the linked Falstad simulation I determined I need 100K resistors to cover the full range. Would this make the output signal high impedance? That is, not quite suitable for feeding directly to an ADC? Would it need buffering first?
This might be a good opportunity for me to try some SMD soldering.
Are the components spaced to tightly?
Doesn't look too bad to me. I would perhaps move the components above and below the op-amp so they are a little further away.
What I like to do when trying to determine whether a layout of SMD components is easily hand-solderable, is to print it out on paper actual size and get my soldering iron in hand (off, of course!) and make sure I can get to all the pads and joints without any other parts being in the way. For example, avoiding having two resistors laid-out with ends facing, but not enough space between to get the iron to the pad of one without risk of touching the other.