[Coco] Project Sneak Peek

Darren A mechacoco at gmail.com
Tue Jul 19 13:26:17 EDT 2016

On Tue, Jul 19, 2016 at 10:49 AM, S Klammer wrote:

> Sorry, I didn't want to ramble... will the 8bit PWM be a single channel
> player, being able to play only a single sample/sound at a time?  At what
> rate(s) will the PWM be able to play at?  Does each channel(s) have a
> separate volume?  Can the playback position be changed during playback?
> What are the header pins for?

It is a fairly simple, single-channel implementation. I only had one pin
available on the micro controller to use for sound. It takes 8-bit samples
from the source (SD card / RAM) at a rate of 8 kHz. Those samples are
converted to a pulse-width modulated output using a carrier frequency of
62.5 kHz.

The PWM / SND female header on the pictured board was for me to test
different capacitors for AC-coupling of the PWM signal to the CoCo's SND
input line. I haven't had much success with this. The results I get are
either sound distortion or the volume being way too low.  A direct
connection without AC coupling seems to produce the best results.

The male header pins are the JTAG interface for programming the CPLD. That
header will not be present on production boards, as the Atmega MCU will
handle that job as well.

- Darren

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