Review of: voltmeter, ampmeter, ohmmeter circuits for Arduino
I'm only doing the voltmeter circuit: -

The LM833 is a rubbish choice - its output voltage capability on a +/- 15V supply is only guaranteed to be +/-12V - this means that on a 3V3 supply you get sweet F.A. out of it. It's not a single rail op-amp: -



Basically it won't work on a supply below +/- 5V.

Neither does it have a power bandwidth of 400 kHz - PB is 120 kHz.

Another problem with the op-amp is the input offset currents may be as high as 200nA - given that you have 1Mohm resistors attenuating the signal and the potential to be feeding the input signal in via 9M1 resistors, the impedance seen by this current is 900kohm. With 200nA flowing you'll have an error voltage of 180mV added to your signal and eating into your error budget significantly.

Input offset voltage is 5 mV and on your low voltage setting (gain of 10) this becomes 50mV on the output. Given that your error budget for this range is 30mV you've blown it!!

I think you should be considering an instrumentation amplifier run from a +/- 5V supply, maybe the AD8221.

It looks like you are misusing the LM833 on the other sections of the question so you get those parts reviewed on that bad choice for free!

I suggest you concentrate on getting one bit right, learn from your mistakes and apply the "learnings" to the next section of the design. In other words reduce this question to the voltmeter part and once you are happy with it being OK ask another question.