using mmc for voice recording

hey folks,

i have been working on the construction of a voice recorder using memory
of MMC and ATmega 16 as the controller associated...i am using the MMC in
SPI mode... since the sampling rate of the data is quite high... so i dont
use any buffer memory before storing data to MMC, i keep the mmc
initialized to a page and keep on sending the samples to the card... and
when a page is full ...a new page is initialized to take in the data... but
i face a problem of varying ground levels in the circuit while the data is
being written... placing an earphone between two ground nodes in the
circuit even leads to some sound which resembles the sound of a helicopter
:(... this is added to my voice recording as the background and is
obviously played back..
i havent been able to figure out a reason for this problem yet.. could u
please help..

On Dec 17, 6:35 am, "chimpi" <tanuj.i...@gmail.com> wrote:
> hey folks,
>
> i have been working on the construction of a voice recorder using memory
> of MMC and ATmega 16 as the controller associated...i am using the MMC in
> SPI mode... since the sampling rate of the data is quite high... so i dont
> use any buffer memory before storing data to MMC, i keep the mmc
> initialized to a page and keep on sending the samples to the card... and
> when a page is full ...a new page is initialized to take in the data... but
> i face a problem of varying ground levels in the circuit while the data is
> being written... placing an earphone between two ground nodes in the
> circuit even leads to some sound which resembles the sound of a helicopter
> :(... this is added to my voice recording as the background and is
> obviously played back..
> i havent been able to figure out a reason for this problem yet.. could u
> please help..

Put some bypass capacitors right at the MMC card (probably a little
low impedance one, and a larger electrolytic in parallel).   And for
every other digital chip, too.

Increase your ground trace thickness.

Consider making your analog and digital grounds almost entirely
seperate and tied together only at the ADC.  Or follow the other
school of thought and use a PCB with a full ground plane tying
everything together with as low impedance as possible.

Use differential circuits in the audio to the greatest extent
possible.