MCU digital input curve

Schematic:

.-----------------------------------------------------------------.
|                         Arduino                                 |
|                                     pin_an_in=A2                |
|                                                                 |
|                          pin_amp_out     |  pin_dig_in=D8       |
|  pin_pwm=D9                              |        |             |
|                              |           |        |             |
'-----------------------------------------------------------------'
       |  100k        MC33201  |        Ain|        |Din
       |  ___            |\    |           |        |
       '-|___|--o--------|+\   |     ___   |        |
                |        |  >--o----|___|--o--------o
               ---      -|-/   |                    |
          100n ---     | |/    |     120           --- 1u
                |      |       |                   ---
                       |       |                    |
               GND     '-------'                   GND
                             Vamp

dig input plot

ATmega88

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

analog value time plot

ATmega88

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