Progress Report on this dead thread:
I got some free time to experiment. I was able to make a attempt
using a ATtiny26. I used the atmel's internal ADC biased to 2.5V with
100K resistors to +5 and GND and audio coupled in with a 0.22uF
capacitor. For the DAC I used a resistor ladder built with 20K and
10K resistors and audio coupled out with a 0.22uF. And I am using a
256Kbit 25MHz bus speed serial nvram for the storage.
It works, But...
Because of the succesive aproximation nature of the atmel's ADC there
is not enough speed to make the project usable. Each conversion takes
between 16uS and 256uS. and a different variable means a different
sampling time. I was able to sustain a sampling rate of about 2.8kHz,
which if you know anything about digital audio means that the best
frequency that can be passed is 1.4kHz. I am doing some math to
convert the 10bit ADC to 8bit for the DAC and to save space in the
RAM, but it is not what is slowing it down as it is a simple Shift
statement.
So, It sounds like ass. But you can hear audio running and I was
supprised by the fact that it actually worked at all. It kinda sounds
like a really bad digital cell phone connection at the moment, or the
sound from a OP-amp that doesn't have negitave voltage to it. The
closer I could get the audio to do a full swing from 0 to +5 or 5V
peak to peak the better it sounded because of utilization of more
bits.
I am now trying to locate 12 or 16 bit ADC/DACs to continue
experimentation, with sampling rates of either 32kHz for 12 and 44.1
or 48kHz for 16bit.
In the future I will use a dual op-amp for the audio in and out as it
will do a better job of biasing to 2.5V than the 2 resistors.
Yahoo! Groups Links
<*> To visit your group on the web, go to:
http://groups.yahoo.com/group/Repeater-Builder/
<*> To unsubscribe from this group, send an email to:
[EMAIL PROTECTED]
<*> Your use of Yahoo! Groups is subject to:
http://docs.yahoo.com/info/terms/
