SX28 with Hardware ADC

herold

I just ordered the SX28 development kit and I would like to sample from my external build white noise generator.

Reading about the virtual programmed AD I came to the conclusion that it is too slow. Do you know of any good AD chip that is simple to use with the SX28? What max sample rate can I expect?

Dave Paton

Herold-

Max sample rate will be as much a function of your program as of the external ADC. With flash ADCs on the market capable of hundreds of millions of samples per second, you're entirely limited by how tight you can code and how much you want to spend.

What do you consider "fast"?
What kind of interface do you need? SPI, I2C, parallel?
What kind of money can you spend on parts?
What else will your processor need to do in between samples?

These are all things we need to know before we can help further...

-dave

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herold

Hello Dave,

Thank you for the reply. Basically I want to sample a signal (white noise) as fast as possible (8 Bit) and than send the sample data via serial to the PC. So, there is not much program vode, I guess.

I am working with Realbasic on the PC and the fastest baud rate there is 500K. So this is my limit. Everything else should be not slower than this.

I already have some AD 8 BIT chips from Maxim (MAX153/Max114) which do up to 1Mhz sample rate.

pjv

Hi Herold;

So what you are indirectly saying the 500Kbits/sec is your choking point.

At 10 serial time bits per 8 bit A/D reading that is 50 KSamples/sec. or 20 Usec per conversion.

I would expect the practical limit on an SX virtual 8 bit A/D would be 50 uSec per sample, and that is at 50 MHz.

But here is a question in approaching your problem in a different (easier?) manner...... why not generate the white noise with a pseudo-random (noise) sequence?

That's real easy to do with an SX.

Perhaps there is a good reason that I don't understand.

Cheers,

Peter (pjv)

herold

Hello Peter,

So what you saying is that the SX is good enough for what I want to do. Yes, I need a true white noise generator (generated with a diode or transistor) for what I want to do.

pjv

Hi Herold;

No, that not quite what I said. At best the SX can probably only do about 20,000 8 bit conversions per second, and you wanted things to run as fast as the maximum serial bit rate of 500 kbits/second, and that translates to a desired conversion rate of 50,000 samples per second. So the SX can't do what you want that way. An external A/D is required and I don't want to spend the time to research for you what you should be able to find on your own.

But can you please explain to me why an SX generated pseudo-noise sequence would not work? You'd be able to get higher frequencies than 8 bits times 50,000 per second.....

Cheers,

Peter (pjv)

herold

Hello Peter,

Thanks for the quick reply. I wanted to use an external AD (MAX153/Max114) because I was aware of the speed limitations on a virtual AD.

I do conciousness research with this tool as the diode act as an transmitter between conciousness and the physical reality. Princeton did a lot of research on it. A pseudo random generator did not work in their experiments.

With an external AD I should meet my requirements, yes?

pjv

Herold;

The external A/D you choose will determine the capabilities.

Please re-read Dave's post above, you need to provide detail as to what you are trying to accomplish in order to get useful help.

Peter (pjv)

Post Edited (pjv) : 7/3/2005 11:03:06 PM GMT