[sdiy] Driving SSI2144 freq control with PWM from a microcontroller

[Gordonjcp]

On Sun, Nov 06, 2022 at 11:50:54PM +1000, Ashlyn Black wrote:
> 
> Attached is two screenshots, both with 30kHz, 0% to 50% duty cycle
> transitions. The top graphs are the outputs of the active topology, middle
> is passive topology, bottom is an overlay.

Throw a few more passives and a buffer at it, and make a 2-pole Sallen-Key filter with a notch filter to follow. As has previously been pointed out to me this makes something approximately like a Chebyshev filter, with the notch chopping off the PWM "carrier" frequency from the "rounded off" PWM out of the lowpass.

In experiments, this produced a PWM-derived output that was as clean as any 8-bit DAC.

-- 
Gordonjcp