Re: [uCsimm] MP3's

From: Micah Dowty (micah@homesoftware.com)
Date: Thu Jul 20 2000 - 23:20:05 EDT


The interrupt-driven audio player is part of ez328monitor. It's a program
for 'ez328 boards that runs without an OS, intended to provide a quick way
to test hardware. You can get the code to that at:
http://kiwi.sourceforge.net/tools.html
For the sound samples, i had been using mpg123 and sox to convert .mp3
files to raw 32khz 8-bit sound samples.
This uncompressed sound can fill up an 8mb DRAM chip pretty quickly
though. As I was just trying to test the hardware I didn't mess with any
compression.

As for the hardware, let me try my hand at ascii graphics :)

   PWM (from ez328) |\ 100uf
          .______ | \ +| | _
          |______>--------| >--------| |-------<*> Headphone connector
                          | / | | |
                          |/ |
                        Buffer * -----
                                                ---

This method works ok (check the current specs on the buffer! Headphones I
tested use about 20ma) for headphones but for anything more powerful you'd
need an amplifier. The capacitor is probably a good idea either way,
because it strips off the DC part of the signal, reducing current
requirements and improving the sound.

On Thu, 20 Jul 2000, David Beckemeyer wrote:

>
> A long time ago, you said:
>
> > I had connected the PWM output (not of a ucSimm but of
> > my Kiwi) to a buffer chip to increase the current. The output from the
> > buffer chip connected through a 100uf capacitor (to remove the DC) to
> > headphones. It plays 32khz audio nicely, and I can fit a good portion of
> > a song in my 8MB DRAM uncompressed.
>
>
> Can you provide the circuit example and/or code samples showing
> how you did this? What did you use for source data format?
>
> Thanks,
>
> - david
>
> This message resent by the ucsimm@uclinux.com list server http://www.uClinux.com/
>

-- 
>From the command line of Micah Dowty

"We all know Linux is great...it does infinite loops in 5 seconds." - Linus

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