Just got an idea to simplify/change the circuit a little.
The diode used to generate the biasing voltage and reference voltage can be replaced with a filtered PWM output - which will give a DC-voltage. The DC-voltage can be directly controlled by changing the duty cycle of the PWM signal (to give a DC voltage from 0 - 5 volt).
I have made a few tests on breadboard, and I'm able to get a good synch with just 4 components. The RC-filter, a diode and the AC-coupling capacitor. A 10K (or something like that) pull-down resistor in the climping circuit might be a good idea.
To use as few components as possible I have used ground as reference voltage
This code can be used to generate fast PWM on pin 9 (OC1A/PB1)
OCR1AL = 207; // Compare register - used to control voltage.