sampling frequency?..

[singaperumal]

we r doing project in biomedical.. we r using adc0808 interface with 8051 to measure the signal from piezo-crystal sensor.. in A to D conversion what is thesampling frequency????

 

[sherazi]

The analog signal is continuous in time and it is necessary to convert this to a flow of digital values. It is therefore required to define the rate at which new digital values are sampled from the analog signal. The rate of new values is called the sampling rate or sampling frequency of the converter.

 

[FoxyRick]

Are you asking how quickly the ADC0801 can sample?

That is given by the datasheet as 100us for each conversion, plus some time for address setup and sample/hold. So, once everything is set and if you do not change anything (other than the analogue signal itself of course), then you can read data at a maximum of 10,000 samples per second (=1/100us).

You can increase the clock speed to double the standard (from 640KHz up to 1280KHz) but there is some fixed overhead in the system so that won't quite give twice the sample rate.

Is that what you want to know?

 

[sherazi]

@foxyRick as far as my understanding is considered he wants to know about the term "sampling frequency"..

 

[RetroTechie]

Ah right, let me Wiki that for you... ;-)

By the way singaperumal, what is that sensor measuring?

 

[Petre Petrov]

Hello!

May be that will help you at least when you sample sinusoidal and co-sinusoidal signals:

“A New Approach to Sampling Sinusoidal and Cosinusoidal Signals”, P T Petrov,
https://www.ieindia.org/pdf/88/88ET104.pdf

Also may be it will be useful to know:
“Sampling of the Simplest Signals” P T Petrov
https://www.ieindia.org/pdf/89/89CP109.pdf

Any feedback is welcomed

BR

Petre Petrov

 

[ark5230]

we r doing project in biomedical.. we r using adc0808 interface with 8051 to measure the signal from piezo-crystal sensor.. in A to D conversion what is thesampling frequency????

You have to provide clock to 0808 ADC, this clock determines the sampling rate in the present case under discussion.
If you can post the details of the ADC circuits, it will be easier for members to attend to the issue.

 

[permute]

Hello!

May be that will help you at least when you sample sinusoidal and co-sinusoidal signals:

“A New Approach to Sampling Sinusoidal and Cosinusoidal Signals”, P T Petrov,
https://www.ieindia.org/pdf/88/88ET104.pdf

Also may be it will be useful to know:
“Sampling of the Simplest Signals” P T Petrov
https://www.ieindia.org/pdf/89/89CP109.pdf

Any feedback is welcomed

BR

Petre Petrov

paper 1:
the conclusion on pg20 is incorrect. There is not any AM. indeed a conversion to frequency domain (fft) will have no spurs. further, the peak values can be interpolated correctly. Only the ADC resolution becomes an issue, as the quantization noise for a periodic signal will itself be periodic.

paper 2:
none of the signals listed have information -- there is no entropy in any of them.

I think you've created some terms that you are comfortable with, as well as redefined some accepted terms.

 

[Petre Petrov]

ark5230 ,
Thank you for the post.
-------------------

Paper 1:
The conclusion on page 20 is correct.
* If you change the phase of the sampled signal you will change the amplitude of the samples and this is a kind of AM of the samples from the phase of the sampled signal
* If you change the angle of the first sample you will change the amplitude of the samples and this is a kind of AM of the samples from the phase of the first sample.
* Fourier series is oversimplified.
* The peak values can be interpolated correctly if you have
1/ enough samples and
2/ enough amplitude of the samples.
OR
1/ if you have enough SSF N and
2 enough number of accurate bits n of the ADC, etc.
*Only the ADC accuracy is important NOT the resolution.
---------------------

paper 2:
* All of the signals listed have information
* Forget the entropy,
* Forget the classical information theory
-----------------------

Conclusions:
* I have created some terms which are supposed to be more accurate or less misleading that the terms in massive use today;
* Yes, I am comfortable with these terms, as well as with the redefined some accepted terms.
* The objective of the post was to help the guy to select the sampling frequency in order to have enough amplitude of the samples and enough samples to calculate all parameters of the basic test signals: SS, CS and SBLS.

I hope that is helpful.

 

[permute]

ark5230 ,
Thank you for the post.

...

Firstly, I would suggest that this side topic be considered for a new thread.
Paper 1 -- you are defining AM based on the peak sample value and not the recoverable peak value of the signal represented by the samples. Using just the sample values would be a fundamental misunderstaning of the sampling theorem. Saying linear transforms (like fourier) are oversimplified without giving more information isn't a strong argument. For the remainder, I didn't look up how you defined your terminology a second time.
Paper 2 -- ok, maybe they have information, but not an information rate (asymtopically 0 due to the lack of entropy). Any irrational ratio of sampling rate to carrier frequency will eventually provide arbitrarily accurate estimates of each of the parameters, even with quantization. Any rational ratio will have some limit as the samples will repeat.

Petre, I don't want to sound harsh. I also rediscover things from time to time. I hope you take a less defensive stance over what even you call "simple signals".

--

The OP hasn't responded, and to my knowledge no one has asked about the signal of interest. It is possible that the sampling rate would be less than the analog frequency of the signal of interest (eg, bandpass sampling).

 

[rohitkhanna]

Max Sampling frequency depends on the Clock frequency you provide. Typically spec'd at 640Khz & 1280Khz in the sheets. But I suppose it could be anything in between as well.

Having selected this clock, then the fastest your ADC can work is when "...Continuous conversion may be accomplished by tying the end-of-conversion
(EOC) output to the SC input.." (from the spec sheet of ADC0808)

Alternately YOU can control the "Start" point of conversion to exactly some fixed frequency, which must be lower than ~10Khz for a 640Khz clock.

So if you want to sample a fixed (say) 5Khz rate, then generate another clock of 5Khz, feed it to the "Start" pin, and read the values as they come out of the ADC at the End of Conversion positive edge.

 

[Petre Petrov]

Hi, permute
Thanks.

Ok, you can put it in a separate threat, but this one is named “Sampling frequency ?” and seems appropriate title for me”.

In all cases singaperumal will be forced to select the sampling frequency nad to test the system.
Although I am still interesting in the topic it seems too complicated for that forum.

The ideas was to tell singaperumal and people like him/her to use 4x or more in order to have better reliability of the samples and better SNR in samples, etc. The amplitude of the samples is vitally important for the system.

Of course singaperumal should read the data sheet of the ADCV and post the schematic diagram

Ok, many people have rediscovered the wheel and etc, so there is nothing bad about that. In almost all cases we do not know who the first discoverer was. Even in our days when everything is recorded the important push or idea for discovering something comes from the outside world, etc.

Defining the simplest signal, how to sample and reconstruct them has vital importance for the measurement in the sampling and reconstruction system.

The clear terminology has vital importance for the advanced in any field.

Usage of samples with enough amplitude plus the equations of the known test signals is the only good way to calculate the parameters of the sampled signals and to evaluate the parameters of the sampling and reconstruction system.

The two definitions of the sampling theorems of C E Shannon are not the same and both definitions are not applicable the sampling and reconstruction systems. Noting can be done to save them. The same is applicable to his information theory.

Fourier is oversimplified, etc.

As a conclusion my position will not change because I do not want to read misleading terms and theories and to mix people like Nyquist and Shannon in the sampling theory. That does not sound good but the reality is like that.

 

[rohitkhanna]

Hi, permute
Thanks.

Ok, you can put it in a separate threat, but this one is named “Sampling frequency ?” and seems appropriate title for me”.

In all cases singaperumal will be forced to select the sampling frequency nad to test the system.
Although I am still interesting in the topic it seems too complicated for that forum.

The ideas was to tell singaperumal and people like him/her to use 4x or more in order to have better reliability of the samples and better SNR in samples, etc. The amplitude of the samples is vitally important for the system.

Of course singaperumal should read the data sheet of the ADCV and post the schematic diagram

Ok, many people have rediscovered the wheel and etc, so there is nothing bad about that. In almost all cases we do not know who the first discoverer was. Even in our days when everything is recorded the important push or idea for discovering something comes from the outside world, etc.

Defining the simplest signal, how to sample and reconstruct them has vital importance for the measurement in the sampling and reconstruction system.

The clear terminology has vital importance for the advanced in any field.

Usage of samples with enough amplitude plus the equations of the known test signals is the only good way to calculate the parameters of the sampled signals and to evaluate the parameters of the sampling and reconstruction system.

The two definitions of the sampling theorems of C E Shannon are not the same and both definitions are not applicable the sampling and reconstruction systems. Noting can be done to save them. The same is applicable to his information theory.

Fourier is oversimplified, etc.

As a conclusion my position will not change because I do not want to read misleading terms and theories and to mix people like Nyquist and Shannon in the sampling theory. That does not sound good but the reality is like that.

What ARE you blathering on and on about ?