PWM sound

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After RP2350 migration we have enough GPIO pins to spare some to play simple PWM sounds.

I have wired a simple audio circuit from RP2040 hardware design document and it works just fine.

This posed a question: How to mix it with output coming off SD-1 synthesizer.

Mix them all together? Mix PWM1 to LEFT channel and PWM2 to RIGHT channel?

Maybe let the user decide? 🤔 So, I started researching digitally controlled audio mixers…

I have found some chips that would fit perfectly, but these are not produced for more than a decade. Fortunately there are some automotive chips still available, which could be repurposed for my goal.

I’ve decided on ROHM BD3461FS mixer. If I merge its 6 output channels into two L/R channels, it would work as we need.

This chip has some unusual pitch, thus putting it on breadboard is also unusual 😜

audio mixer breakout board

It is wired as follows:

Then I tried, whether playing sampled sound over PWM works…

audio schematic