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40 Potentiometers measuring — Parallax Forums

40 Potentiometers measuring

ronnarronnar Posts: 2
edited 2004-12-09 17:48 in BASIC Stamp
Hi:

Is there anyone who can help me?

I need to manipulate the data from 40 potentiometers (angle positions) measured at the same time,·in a PC program under XP.
I think I need an analog digital converter, to convert the analog information into binary one and then convert it in decimal and finally in degrees (the angles to measure are less than 200 degrees)...but this is good for a single POT...
But this is not the only problem...I also need measuring those angle positions in a 1/20 second lapse (aprox), so it must be 20 measured positions per second,·for each sensor...·800 per second·in total...

My question is : Can I do this with the Basic stamp?, and· Exist an A/D converter with all those channels?..and for the lapsed time measuring Can I use some kind of clock like the 555??....

thanks very much

Comments

  • Jon WilliamsJon Williams Posts: 6,491
    edited 2004-12-07 18:49
    You might want to gang three ADC0838 ADCs to the BASIC Stamp, that would give you 24 analog inputs. Speed? You might want to use a BS2p for speed, and your transmission rate of that data to the PC will be a factor.

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    Jon Williams
    Applications Engineer, Parallax
    Dallas Office
  • steve_bsteve_b Posts: 1,563
    edited 2004-12-07 18:59
    Hey Jon,

    This question brings a thought....

    Is there any ADC's that offer triggered capturing?· Basically, if I have 3 ADC's with a whack of I/O's, and sensors connected to those inputs, if I send a read command or an enable (whatever the event to cause them to read their inputs) will the ADC(s) hold the info there until I tell it to read again?



    I'm thinking of doing 'snapshots' of system performance.· Where I could get a number of readings captured at once and then take my time reading them with the stamp until I determine it's time for another reading. (twice a second? maybe once a second!)....

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    ·

    Steve
    http://members.rogers.com/steve.brady
    http://www.geocities.com/paulsopenstage

    "Inside each and every one of us is our one, true authentic swing. Something we was born with. Something that's ours and ours alone. Something that can't be learned... something that's got to be remembered."
  • K de JongK de Jong Posts: 154
    edited 2004-12-07 19:00
    Hi Ronnar,

    You allso could use 4 x TLC2543 (Texas Instruments), they give you 11 channels of 12 bit accuracy each. So in total 44 cannels. You will need 7 Stam pins in total.

    You will have to do something clever with you data and/or memory. 40 Words will not fit into the normal ram of a Basic Stamp.

    Regards,

    Klaus
  • achilles03achilles03 Posts: 247
    edited 2004-12-07 19:28
    Ronnar,
    Can you describe your application in a little more detail? What exactly are you calling a "potentiometer"? (maybe a PN?) If you're just trying to measure the angular position of, say, a wheel, you COULD use just one.
  • allanlane5allanlane5 Posts: 3,815
    edited 2004-12-07 19:39
    One of the multi-channel ADC (Analog to Digital Converter) I know of multiplexes 8 Analog inputs into a single AtoD converter on chip. Thus, you must select a channel, start the conversion, wait a while, read the data, select the NEXT channel, and repeat.

    What you'd like to do is kick off conversions on multiple channels, wait a while, then read each of the multiple channels.

    Read the ADC specs carefully to get the scenario you want.
  • ronnarronnar Posts: 2
    edited 2004-12-09 14:38
    Hi,·Jon·· , thank you very much for your reply!!!
    I have a few questions for you:
    Instead the three ADC0838, Can I use three ADC0817 (8 bit A/D converter with 16 channels multiplexer)?
    Or handling 40 channels used at the same time, is too much for the Basic Stamp?
    And, remembering that I need (only input to PC, not output) data acquisition with a "capturing rate" between 1/10 sec and 1/20 sec (aprox), Can I use the BS2, or the BX24 (BasicX24) instead the BSp2? Or there are too slow for the job??
    Thank you very much and best regards for you
  • Tracy AllenTracy Allen Posts: 6,658
    edited 2004-12-09 17:19
    I think 800 analog measurements per second is a stretch for the BS2p even. To approach that rate, I would go for an multichannel ADC that is capable of burst operation, to convert all of its channels with one operation. For example, the MAX1038, 12 channels, so 4 of them for 40 channels. You set all of them up for burst mode. Then loop through the 4 of them reading in all 12 bytes of data, and immediately send it out at 56200 baud. The data transmission will take most of the second, so it still might not be fast enough for you. But then move it to the new SX/B compiler--Made in the shade.

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    Tracy Allen
    www.emesystems.com
  • achilles03achilles03 Posts: 247
    edited 2004-12-09 17:48
    Yeah, 800 samples/sec probably won't be obtainable with the BS2p. With the BS2, the fastest I've been able to shiftin (and write to EEPROM) single byte samples from a single-channel 8-bit ADC (no addressing time required) was 167 samples/sec.
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