AVR-Chat

Hello again!

I drew out a quick schematic for the AC coupling.  I wasn't sure 
exactly how to wire it up.  Can you take a look at it and let me know 
if it's what you mean? 

The values of the capacitor pictured are wrong.  Don't worry about 
that: 

http://www.voxglitch.com/images/coupling_test.bmp

Also, was there any advice for me on how to NOT clip the lower half 
of my audio signal when doing the A/D conversion?

Thanks a ton!
- Bret


--- In AVR-Chat@yahoogroups.com, "c45a6" <clone45@h...> wrote:
> 
> Oh, poop.  I just lost a huge e-mail response.  Argh.  
> 
> In short, thanks for the advice!  Speeding up the ADC really 
helped.  
> It's still distorted, but I can now hear notes and lyrics. :-)
> 
> Tomorrow I'm going to post again asking more questions about the AC 
> coupling.  I'll whip up a schematic to help out.  Am I still 
cutting 
> out 1/2 of the audio signal, even after the ac coupling?
> 
> Thanks!
> - Bret
> 
> --- In AVR-Chat@yahoogroups.com, "Larry Barello" <yahoo@b...> wrote:
> > You can speed up the ADC by specifying a small clock divisor.  
The 
> default
> > is around 64 or 128, but you can specify 8x or even 4x and get 
much 
> faster
> > conversions.  The accuracy will suffer, but, so what.  With a 
4mhz 
> clock and
> > a clk/4 ADC clock, each conversion will take 13 us for a 
conversion 
> rate of
> > ~76k/s.  Hmm, I guess clk/8 will give you ~38khz conversion which 
> should be
> > plenty good.  Read the BASCOM help for "config adc" and 
> replace "auto" with
> > 4 or 8 (or whatever) to get the faster speeds.
> > 
> > To AC couple your signal, you need a capacitor between the ADC 
> input and
> > your signal.  Use your Vcc/2 to bias the ADC side of the 
> capacitor.  The
> > size of the resistor and the capacitor will be somewhat 
important, 
> but alas,
> > my electronic theory can't help you here with hard numbers.  Try 
> 10k + .1uf
> > ceramic cap to start.
> > 
> > Cheers!
> > -----Original Message-----
> > From: c45a6 [mailto:clone45@h...]
> > 
> > >
> > > Try hopping up the A/D to 250kHz, and using all 8 bits.
> > > AC Couple your audio, and weakly (10k?) pull the A/D input to
> > >VCC/2, and use VCC as your analog ref.
> > 
> > Thanks for the fast response!  I have some follow up questions.
> > 
> > 1. Er.. How do you hop up the A/D to 250kHz?  Do you set the ADPS
> > bits of ADCSRA?  I'm using the internal clock.  Is that a big no-
no?
> > 
> > 2. "pull the A/D input to VCC/2" Sorry, my electronics language
> > skills are terrible.  Do you mean run a pull up resistor (around 
> 10k)
> > between VCC/2 and the A/D input pin?  I just happen to have a 
VCC/2
> > source on my board already that I use for the reference voltage on
> > the D/A converter.
> > 
> > 3. How does one AC Couple the audio?  Do you have any links to
> > schematics for that?  My pathetic little electronics books don't
> > cover that subject. :-(
> > 
> > A million thanks!
> > - Bret