I just registered here for this topic.
I am planning to build a dimmer and I want it to be based on the FL5150 as the dimming controller and an arduino/atmega328 to control the FL5150

I am not very confident in my understanding of this chip, so here's what I assume (btw: It would be nice if someone could :

• DIM Control has an internal pullup resistor (otherwise the potentiometers would have to be used as a voltage divider between VDD and GND instead of just being connected to GND).
• VDD can source at least some current for external components (otherwise it would be useless, since DIM Mode has a pullup resistor according to the datasheet so to choose between trailing and leading edge, you just have to either short DIM Mode to ground or leave it floating)

Under those assumptions, my first idea was to drive a reasonably fast optocoupler with a PMW signal from my MCU and put that optocoupler between GND and DIM Control pins. Unfortunately, DIM Control is not suited for receiving a PMW signal (as per https://www.onsemi.com/PowerSolutions/faq.do?method=faqs&wpn=FL5150).

Then I thought about adding a low pass filter between the optocoupler and DIM Control, but I'm worried I will end up with my signal being either too slow or too unsteady.

So using a DAC or digital potentiometer sounds good, thanks for the idea. But since I have no knowledge of these components whatsoever, can anyone point me to the right one? I would like to have a DAC or digital pot that works with PWM instead of a serial connection, so I can still keep my optocoupler and have galvanic seperation between the high voltage AC and the low voltage DC parts of my circuit.