hi
in the article you linked to, the LM 2917 is actually doing frequency-to-voltage conversion... Looks like a robust and accurate way to do it. You could go with a few diodes and a capacitor ( i.e. ac-dc conversion), but you would lose the frequency, which presumably represents how fast the motor is turning. The best thing might be to just use their design, but repolace the meter with an Ardiuno analog pin.
D