[Coco] Cartridge Port Sound

[Darren A]

On Sun, Dec 27, 2015 at 11:46 AM, Gene Heskett wrote:

> On Sunday 27 December 2015 13:15:28 Darren A wrote:
>
> > I want to connect an IO pin of an AVR micro controller to the SND
> > input line on the CoCo cartridge port. The IO pin will be outputting
> > PCM audio. Can anyone describe the proper way to do this? The Service
> > Manuals mention that it needs to be AC coupled.
> >
> Yes.  Try a .05 capacitor in series with it, if no bass, try a .5.
>
> But the coco's audio  doesn't know what to do  with PCM audio, so we'll
> need to know the output clocking speed of the AVR, with an eye toward
> using a simple low pass filter to integrate the encoded but digital
> signal into something resembling an analog audio. If its too slow, say
> less that 50 kilohertz for the clock, the filter might get more complex
> than a simple rc rolloff.
>
>

It is playing audio sampled at 8 kilohertz using a carrier frequency of
62.5 kilohertz.

- Darren