MCU output pin IV curve

Schematic:

.-----------------------------------------------------------------.
|                         Arduino                                 |
|                                                                 |
|                                                                 |
|                         pin_amp_out=A1                          |
|  pin_pwm=D9                              pin_out_an=A3          |
|                              |                 |pin_out_dig=D10 |
'-----------------------------------------------------------------'
       |  68k       MC33201    |                 |     |
       |  ___            |\    |                 |     |
       '-|___|--o--------|+\   |     ___         |     |
                |        |  >--o----|___|--------o-----'
               ---      -|-/   |
          100n ---     | |/    |   R=120
                |      |       |
                       |       |
               GND     '-------'
                             Vamp              Vout

io iv plot

ATmega88

(Source code, png, hires.png, pdf)

analog value time plot

ATmega88

(Source code, png, hires.png, pdf)