This is phenomenal! Kinda. I have tried on multiple occasions to communicate with a serial port. Granted, I was using PERL on a Windows machine, and was trying to manipulate the state of a servo controller, so the circumstances were a little different. I found that just about anything was abnormally difficult through the Win32::SerialPort interface (either that, or I was missing something).

I will certainly be examining the source to this nifty lil’ project. It appears to be easier than I had imagined to do this kind of thing in C. I’m sure me and the termios.h header will become best of friends. :)

Wow, this is heavy nostalgia for me. I remember having a similar commercial-built device hooked up to my parallel port about eleven years ago, playing sound with just about the same quality.

Nostalgia all right: I remember even having serial ports.
(Mac owner. :-)

Damnit, that’s the third time I’ve misspelled someones name in the last week. I’ve gotta stop writing these things at 5 am.

woah, I’m smellin’ another sweet way to crustify those synth tracks!

An RC filter and amplifier is definately required. Serial port probably won’t like it if you hook up your headphones.
And doesn’t sigma-delta modulation require an integrator? Perhaps they meant DPWM? (discontinuous PWM, dithering PWM, digital PWM)

the site’s back up, but coral cache hasn’t caught on yet. Click on my name for the direct link.

darkfader, the integrator is in software. See the block diagram. the PWM techniques you mentioned are suited for power inversion, not audio.

You can get by without a filter (at high baudrates) because sigma-delta shapes the noise up in frequency. For example at 115200 baud, a zero signal would get modulated to a 115.2 kHz square wave. You can’t hear it. Your speakers can’t play it. When you start trying to play more interesting signals, the noise moves down the spectrum, but it concentrates near the top.

Check out http://www.k9spud.com/traxmod/ for something like this using a dsPIC and an SD Card. Uses the PIC’s PWM feature to play the audio off of an SD Card. Plays raw wave audio or 4 channel MOD music files.

Thanks for the S-D link darkfader. That’s much better than the information I was working with. Or the incomprehensible wikipedia article.

Hmm, I wonder if a higher-order converter would sound better…

I’ve been using POKE commands on the Apple IIe to toggle the speaker. There is actually a range of POKE commands/addresses that you can use:

POKE -16336,0 to -16321,0 toggles the internal speaker. The second address (0) can range from 0-250 to alter the pitch.

POKE -16337,0 to -16352,0 (also 0-250) toggles the speaker but sends it straight out thru the cassette ouput to mixer. And oh what a fat, fat sound!

But you are right, $c030 is the same as -163336.

Now if I could only do the same on the Tandy 102….

Ronnie James Dio – RIP