Z-wave PWM Controlled Fan

I wanted to use Home Assistant to speed regulate a fan I will use for ventilation of a small room. Home Assistant is setup so I can use Google Assistant to voice control the fan, i.e. "Set ventilation to 50%".

I have a Qubino Z-wave dimmer that generates a 0-10V output that unfortunately cannot power a fan (to little current). I use the 0-10V output for the Arduino to generate a PWM-signal that controls the fan. The potential of the 0-10V output is divided in half with two 5100ohm resistors so the signal to Arduino is 0-5V. The fan and the Z-wave dimmer is powered using a 12V DC-plug.