chickenfeet
Electrical
- Sep 30, 2004
- 1
Hi all,
>
> I am attempting to encode audio signals using an
> internal ADC of an Atmel microcontroller and
> subsequently playback using either the PWM method or
> a
> DAC.
>
> I have tried using the PWM and the playback audio is
> acceptable with a sampling frequency (also PWM freq)
> of ~31KHz, 8 bit ADC. The output of the PWM is
> connected to a 5th order filter to remove the higher
> freq.
>
> Question
>
> 1. The PWM method produces a background noise
> similar
> to the sound of raining. Could this be due to the
> unclean filtering of the higher frequency generated
> from the PWM square wave ? It seems that the only
> way
> is to generate the PWM at a much higher frequency,
> so
> as to effectively reduce the noise through
> filtering.
> Can anyone recommend any chips or controller that
> can
> generate a symetric PWM (freq and phase correct) at
> a
> higher freq ?
> Or can anyone advice on a good filter that provide a
> cutoff at around 8KHz?
> Any advice is very much appreciated. The PWM freq of
> the Atmel uC are at the max although the ADC can
> goto
> at least 500KHz.
>
> 2. I have also recently tried using DAC to produce a
> much better playback quality. I have choosen DAC0800
> since it is the cheapest around. Unfortunately, the
> output is not what i expected. I wonder where i went
> wrong. The output resembles spikes of varying
> amplitude. The amplitude is very low, in the range
> of
> 10 mV. I connect the -V and +V to 0V and 5V
> respectively. For the DAC output, i connect to an
> inverting amplifier with the feedback resistor the
> same value as to the one connected to both the -Vref
> and +Vref. The +Vref is connected to 5V through the
> resistor and the –Vref to GND. The datasheet never
> mention on the possibility of positive range
> operation, but recommends that the -V be connected
> to
> -10V.
>
> Please advice,
> - If i can use 0V to 5V.
> - Any completed circuits based on DAC0800?
Currently i am reading up on DAC0830
>
>
> Thanks and have a nice day.
>
>
> I am attempting to encode audio signals using an
> internal ADC of an Atmel microcontroller and
> subsequently playback using either the PWM method or
> a
> DAC.
>
> I have tried using the PWM and the playback audio is
> acceptable with a sampling frequency (also PWM freq)
> of ~31KHz, 8 bit ADC. The output of the PWM is
> connected to a 5th order filter to remove the higher
> freq.
>
> Question
>
> 1. The PWM method produces a background noise
> similar
> to the sound of raining. Could this be due to the
> unclean filtering of the higher frequency generated
> from the PWM square wave ? It seems that the only
> way
> is to generate the PWM at a much higher frequency,
> so
> as to effectively reduce the noise through
> filtering.
> Can anyone recommend any chips or controller that
> can
> generate a symetric PWM (freq and phase correct) at
> a
> higher freq ?
> Or can anyone advice on a good filter that provide a
> cutoff at around 8KHz?
> Any advice is very much appreciated. The PWM freq of
> the Atmel uC are at the max although the ADC can
> goto
> at least 500KHz.
>
> 2. I have also recently tried using DAC to produce a
> much better playback quality. I have choosen DAC0800
> since it is the cheapest around. Unfortunately, the
> output is not what i expected. I wonder where i went
> wrong. The output resembles spikes of varying
> amplitude. The amplitude is very low, in the range
> of
> 10 mV. I connect the -V and +V to 0V and 5V
> respectively. For the DAC output, i connect to an
> inverting amplifier with the feedback resistor the
> same value as to the one connected to both the -Vref
> and +Vref. The +Vref is connected to 5V through the
> resistor and the –Vref to GND. The datasheet never
> mention on the possibility of positive range
> operation, but recommends that the -V be connected
> to
> -10V.
>
> Please advice,
> - If i can use 0V to 5V.
> - Any completed circuits based on DAC0800?
Currently i am reading up on DAC0830
>
>
> Thanks and have a nice day.
>
