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microcontroller advice? how to go about this...

Hey everyone,

I have a challenging project ahead for a large university and I was wondering if someone could give some advice on what the best way to go about this is...

Essentially what we need done is to read in about 32 ->64 (or more, eventually, if possible) analog samples every millisecond - preferably about 12-bit accuracy or better (my advisor said that, I'm not convinced that 8 isn't fine too, but we'll see). Storing about 1/4 -> 1/2 a second's worth of data to run algorithms on and look for patterns. Also, it'd be nice (but not vital) to be able to transmit all that information to a computer, which would probably require USB (alternately, we could probably hook up the connection to some hardware in parallel, so the data doesn't *need* to be fed through the controller).

Issue #1- So, 64 analog samples/millisec - coming from 64 different probes - any advice on some kind of an 'analog multiplexer'? Can such a mux switch fast enough to support that kind of data reading? I see ADCs tend to get to 100-200 ksbs, so that part should be alright. What's the best way to go about being able to read all this data from different sources?

Issue #2- Second, enough memory to hold 250 or 500 sets of data, that's also fast enough to keep up with this rate of reading/writing. Worst case: 16 bits

-> 2 bytes * 64 samples * 500 ms = 64 k of RAM just for this. Can get down to 32 K or sure with 1 byte data, or 250 ms, or some reasonable combination.

Issue #3- Preferable, but optional: To transmit all that data to a comp we're talking 128 K/sec = 1 mbps - so we'd need USB, probably USB 2.0 - what does USB 1.1 get realistically?

Issue #4- Would I need a separate interface through the normal I/O pins be able to send a signal back to those original location (to stimulate the tissue there). Is there any other way to do that?

So... Any advice on a chip that can handle all of that? Not to mention that it still needs to be fast enough to do computation on top of it, with all the data in memory. Would it be wise to have dedicated ADC chip that I've seen to do the gathering and a separate ucontroller for the rest? Cost is a minimal concern as this is for a large research university.

Thanks guys!

-Fred

Reply to
Fred Trinkoff
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I look at it a bit differently. Instead of ONE micro doing all, I'd use 8 micros, each handling the tasks for 8 analog inputs,data collection,and transmitting to the host. Reliability.If one of the micro 'hangs', the other 7 still send data. Cost. Cheaper in the long run to have 8 smaller micros than one big one,esp. since they are all identical. Speed. Less to do per micro ,now the 'bottleneck' will be the PC interface(USD or ???) hth j

Reply to
j.b. miller

Let's see: 64 analog samplese/millisec = 64,000 samples/sec X 64 probes =

4,096,000 probe-samples/second. That's a lot of data for one micrcontroller. If you wanted to do this with one ADC and a mux, you would need to perform each conversion in 1/4,096,000 seconds or 244 nanoseconds. Not gonna happen.

I think you need to plan on more that one ADC. Maybe plan on 64 ADCs in your system.

What?! You want to sample 64 probes 64,000 times per second, at

12-bits/sample but you only want to hold 500 sets of data? Let's say we get extravagant and plan for 1 second of data, that would be 4,096,000 samples X 1.5 Bytes/sample = 6,144,000 Bytes or 6000Kbytes. I think you memory requirement estimates are off by 10X (at least).

Forget USB, you are going to want 100Mbit/second Ethernet for this application. Maybe Gigabit Ethernet! You'll also need more memory, wait I already said that.

What in the hell are you talking about? Oh don't mind, we (usenet) really don't care anyways.

No single "chip" can handle all of this. You are describing a data aquisition system the kind of which exists at Los Alamos or maybe a national air-traffic control system. You can't do this with an '8051 or even an '8051 derivative!

Good, because you should be planning on a long, arduous, and expensive development effort if you are planning on building this system from scratch! Why don't you visit the web sites of some companies like HP, Tektronix, and others and see about purchasing this equipment?

Reply to
Bob F.

Bob F. schrieb:

I think you completely misunderstood this.

As far as I understand, he was referring to 64 samples per ms, not 64*64. The information that the 64 samples are data coming from 64 different probes would not have been necessary (and seemingly confused you).

I think though it would be possible with a single uC system, the approach mentioned by j.b. miller is probably more efficient: let a bunch of small and cheap 8-bit uCs process portions of the data, independently. Eventually add a dedicated uC for communication with the PC to reduce the number of interfaces.

--
Dipl.-Ing. Tilmann Reh
Autometer GmbH Siegen - Elektronik nach Maß.
http://www.autometer.de
Reply to
Tilmann Reh

Do you need to build many such devices or is it one off. If it is a one off, then I 'd go with multiple 12 bit ADCs with an SPI interface. Then you connect that to a nice high end CPU with Ethernet. (AT91RM9200 :-) More expensive than the multiple 8 bitters, but probably higher quality on the ADC. USB is not so easy to work with. TCP/IP is supported in a much better way by the industry.

-- Best Regards, Ulf Samuelsson snipped-for-privacy@a-t-m-e-l.com This is a personal view which may or may not be share by my Employer Atmel Nordic AB

"Fred Trinkoff" skrev i meddelandet news: snipped-for-privacy@newsstand.cit.cornell.edu...

Reply to
Ulf Samuelsson

I'd consider distributed uc system with 100Mbit/s Ethernet connection to the computer. You will get good and well defined bidirectional I/O channel and necessary modularity. Besides, you will be able to simulate all the troughput on several standard computers.

Reply to
Alexander Baranov

news: snipped-for-privacy@newsstand.cit.cornell.edu...

Go for 12 bit, or more. This sounds like a large snap-shot logger, and it is poor design to scrimp on the front end specification.

The 91RM9200 would be a good choice for Host, esp as you way the PC connection is 'nice, but not vital'. A higher end uP like the 9200 would also remove the the real-time aspect from the PC, but the PC can still be used for spread sheets :)

For the 'Spread 12 bit ADC' fabric, look also at small uC with 12 bit ADCs, as they can cascade and syncronise better/easier than a sea of SPI ADC devices. eg look at

formatting link

they do High performance Analog+SPI+uC, with ADC specs of 12/16/24 bits

SPI uC can be set up to all sample/trigger their ADCs on a single edge, and then cascade-shift all data in frames. Think of them as smart-ADCs, not as uC. Eval Boards are available for all these above devices.

-jg

Reply to
Jim Granville

Hi Fred,

I suggest you check the Zilog z8 encore CPU which contains up to 12 channel 10-bit A/D converters with continues conversion mode and DMA mode operation. The chip contains up to 64K Flash for the program and 4K ram . I propose that it would be easier to handle to create some kind of a modular expandable systme rather a single system . Multiple z8 could communicate throught SPI interface.

Another way you could address this problem is to use auto(free) running converters, one per channel and to use a FIFO like the averlogic AL422b or AL440B. Then use any microcontroler you like to scan the FIFO devices .

The second method requires more hardware components, pcb size and cost but very litle programming while the first one minimizes size of board, is more cost effective but requires considerable more programming effort.

Regards, Viron Papadopoulos.

Reply to
Viron Papadopoulos

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