gnupic: Need EE/Flash ROM recommendation
Subject:
Re: Need EE/Flash ROM recommendation
From:
Byron A Jeff ####@####.####
Date:
4 Nov 2004 13:45:17 +0000
Message-Id: <20041104134511.GD8848@cleon.cc.gatech.edu>
On Thu, Nov 04, 2004 at 09:55:12PM +1300, David McNab wrote:
> Hi all,
>
> Hoping to draw some interesting ideas from you experts out there.
>
> The situation is that my project is calling for playing audio samples.
> The need is for a fair amount of reasonable quality audio (say, 32k
> frames/sec @ 8 bits/frame stereo), which calls for a high-capacity ROM -
> say, 4-16Mbit or more.
>
> My idea is to create a bunch of audio samples, including voice, sound
> fx, bits of music etc, and burn them into a ROM
>
> Then, to run pins from the PIC into chained serial/parallel shift
> registers, through to the ROM's address bus. Then, from the ROM's data
> bus to a DAC, and out to an audio amp.
Since it's sequential, you could easily get away with counters to access the
memory. Or if you use a 40 pin PIC, you could access it directly.
One good possibility is using MMC chips, which has a high speed SPI interface
IIRC. Since many PICs have hardware SPI interfaces, interfacing would be
really easy.
Here's a "slightly used" 16MB one that $9 USD including shipping on E-bay:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=3850410877&refid=store
>
> Question - can anyone recommend a good chip to use with the PIC?
> Am I taking a hard road here - is there an easier solution (such as
> 'sample playing' chips with inbuilt DACs and an easy h/w interface?
Of course there are. But you may want to try a PIC only solution first. The
basic idea is to crank up the hardware PWM and run it through a low pass
filter. 78 Khz should get you sufficient audio bandwidth. Then you read the
samples at the sample rate and set the PWM duty cycle to the value of the
sample. The output should be decent quality audio with no addtional parts.
I can't get to the article right this second but here is a link to a EDN
magazine article that decsribes the process:
http://www.reed-electronics.com/ednmag/article/CA240913
Hope this gives you some ideas.
BAJ
