"Rene" <invalid@invalid.com> schreef in bericht
news:D6-dnXOuP57TU0zbnZ2dnUVZ8ternZ2d@edutel.nl...
Many thanks for the replies! I am sorry for my late reply.
Yours sincerely,
Rene
Reply by TT_Man●August 27, 20072007-08-27
"Rene" <invalid@invalid.com> wrote in message
news:D6-dnXOuP57TU0zbnZ2dnUVZ8ternZ2d@edutel.nl...
> Hello to all of You,
>
> Being completely new to AVR's and still studying their "anatomy" and
> reading about them I have a question that could probably be solved by an
> experiment but at this moment a real life experiment like this is beyond
> my capabilities and I am a bit nervous to find the answer because it is
> important for a plan I have in my head :-). I hope You might be able to
> give me the answer.
> At the moment I am just making some led's blink and extending the luxury
> of the blink program (first step from now: use timer) but later on I want
> to make a program that reads the value of an analogue signal and then
> (a.o.) "translates" this value into the duty-cycle of the build-in PWM of
> the device. For this I would put the ADC into free running mode. In some
> tutorial (unfortunately I have no idea where it was) I read that one
> should not change the level on an output pin while an AD-conversion is
> taking place because it might ruin the outcome of that conversion. In the
> datasheet I have not read this but they do describe that the ADC can be
> used while everything else in the chip is "silent" to cancel noise from
> the measurement. The accuracy is not very important for my plan. But it is
> important that the i/o pin is being changed constantly by the PWM-unit,
> and the ADC should keep on running.
> By now You will have guessed what the question is: Was the information I
> read correct or is it just a matter of a slightly decreased accuracy to
> have both systems (=ADC and PWM) running simultaneously?
>
> Thank You very much in advance!
> Yours sincerely,
> Rene
Just do it.... you may get the odd error in the ADC but it doesn't matter in
this application... You could save the ADC values in an 8 byte fifo, average
them ( sum and divide by 8) and use that for the pwm.
Where it might matter is if you were making a data logger to record
accurately the ADC values...
Reply by larwe●August 27, 20072007-08-27
On Aug 26, 2:03 pm, Rene <inva...@invalid.com> wrote:
> By now You will have guessed what the question is: Was the information I
> read correct or is it just a matter of a slightly decreased accuracy to
> have both systems (=ADC and PWM) running simultaneously?
This isn't characterized. What I suggest you do is write some software
to capture from the ADC into RAM. Tie the ADC input to a fixed
voltage. Run this software once with the PWM operating, and once
without. Look at the distribution of the ADC output values, and
compare.
I have a project that uses ATmega169, which also has the ADC sleep
mode. I did some tests with and without sleep mode and observed no
statistically significant difference in the noise when using sleep
mode vs. leaving the core running full-tilt.
Reply by Rene●August 26, 20072007-08-26
Hello to all of You,
Being completely new to AVR's and still studying their "anatomy" and
reading about them I have a question that could probably be solved by an
experiment but at this moment a real life experiment like this is beyond
my capabilities and I am a bit nervous to find the answer because it is
important for a plan I have in my head :-). I hope You might be able to
give me the answer.
At the moment I am just making some led's blink and extending the luxury
of the blink program (first step from now: use timer) but later on I
want to make a program that reads the value of an analogue signal and
then (a.o.) "translates" this value into the duty-cycle of the build-in
PWM of the device. For this I would put the ADC into free running mode.
In some tutorial (unfortunately I have no idea where it was) I read that
one should not change the level on an output pin while an AD-conversion
is taking place because it might ruin the outcome of that conversion. In
the datasheet I have not read this but they do describe that the ADC can
be used while everything else in the chip is "silent" to cancel noise
from the measurement. The accuracy is not very important for my plan.
But it is important that the i/o pin is being changed constantly by the
PWM-unit, and the ADC should keep on running.
By now You will have guessed what the question is: Was the information I
read correct or is it just a matter of a slightly decreased accuracy to
have both systems (=ADC and PWM) running simultaneously?
Thank You very much in advance!
Yours sincerely,
Rene