PWM sound
- smokku
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.
- Synthesizer has two output channels.
- We have two PWM channels.
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 😜
It is wired as follows:
INF1
/2
- Yamaha SD-1 synthesizer
INR1
/2
- line-in cinch (x2)
INS1
/2
- expansion port (to allow sound card type expansion)
EXT1
- PWM channel 1
EXT2
- PWM channel 2
EXT3
- expansion port
OUT*1
/2
- line-out cinch (x2) - three pairs joined together, so there is a mix of all IN-puts.
Then I tried, whether playing sampled sound over PWM works…