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

[Tom Wiltshire]

> On 5 Nov 2022, at 11:40, Mike Bryant <mbryant at futurehorizons.com> wrote:
> 
> I'll second using PDM, which I've used since the 1980s on all sorts of products. not just synths.  Better results from DC up to high audio frequencies.   
> 
> The easiest way to get PDM is just to reverse the bits from the PWM counter to the PWM comparator, but not all MCUs support this mode.

Oooh, that's clever! I'd never seen that before. That should *absolutely* be a hardware feature on every chip with PWM. Dead simple to do at the silicon level, and offers a big improvement over not doing it.

The way I know is using an NCO set to output a single pulse when it overflows. Using increment values up to the full maximum value of the accumulator gives you "overflow pulses" that are output more frequently with larger increments - PDM.


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