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Need to find a Analog to Digital Converter IC to do

Discussion in 'Electronic Components' started by Gaetan Mailloux, Jun 13, 2007.

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  1. Hello


    I would need to find a Analog to Digital Converter IC to do data acquisitions
    with a Pc computer using the parallel port.

    Anyone know some analog to digital converter IC with sampling rate over 400
    khz who can be good for that ?

    Thank

    Gaetan
     
  2. IMO your problem would not be getting a simple ADC for doing that, the
    major prob I see is getting 400k/sec over a parallel port. What about
    a simple microcontroller doing the ADC for you and sending the data
    via RS232? BTW, wich accurcy, resolution, ...?

    For 8bit it should be possible with data rates of modern RS232
    equipment. (e.g. 460800 baud = quad 115200) You will avoid timing
    probs due to the non realtime OS, too.

    Regards,
    Heinz
     

  3. Hello

    RS242 , it's the serial port, I was think that the serial port was slower ?

    If I'm understanding right, you do not talk about the USB port ?

    If RS232 are ok, what ADC ic do you suggest for a very simple
    implementation and schematic ?

    Thank

    Gaetan
     
  4. (Gaetan Mailloux) wrote in
    Serial is slower, but RS-232 is a protocol, also used over USB. I think it
    could be very fast over USB2.
     
  5. Jean-Yves

    Jean-Yves Guest

    not if you send a lot of small amount of data...
    it can be fast if you send a few big amount of datas...
    this is due to the number of headers that the usb protocol needs...
    rs232 is not used over usb, it's totally different...
    i think you make a mistake with usb to rs232 converters...
     
  6. Possibly, or maybe it was a mistake already by the time it was told to me.
    I knew a guy who said he was making an in-car MP3 player that was using
    RS232 control signals over USB. I assumed he knew what he was doing, it
    wasn't something I knew about, I just remember that bit of conversation.
     
  7. Dave Platt

    Dave Platt Guest

    Possibly, or maybe it was a mistake already by the time it was told to me.
    I knew a guy who said he was making an in-car MP3 player that was using
    RS232 control signals over USB. I assumed he knew what he was doing, it
    wasn't something I knew about, I just remember that bit of conversation.[/QUOTE]

    It may not have been a mistake. Many newer "legacy-free" PCs don't
    have RS-232 serial ports. In order to connect these PCs to devices
    with an RS-232 interface, one uses a USB-to-RS-232-serial adapter...
    USB device port on one side, RS-232 interface (or several of them) on
    the other.

    Unfortunately, as with most other USB device classes, the protocol for
    talking with such adapters isn't entirely specified by the standard,
    and it's usually necessary to have a different host driver for each
    vendor's USB/RS-232 adapter. Generally, one reads and writes data
    over USB to/from a USB bulk-data endpoint, and sends small control
    packets to another endpoint to read the device status and control the
    RS-232 handshaking lines.
     
  8. Depends of your PC's implementation. Standard speed is up to 115200.
    But many modern RS232 implementations can go up to 8x115200.
    Yes, serial, also not via RS232 to USB converters.
    Almost every simple _CPU_ (not a standalone ADC) should be able to do
    that, e.g. the Silabs CPU C8051F064. ADC Sampling rate up to 1MSample,
    and the serial port should be able to do the 400kbit speed.

    If you are not that familir with an solder gun give the development
    kit a try. Ready to use, including an JTAG interface for programming.

    Heinz
     
  9. CWatters

    CWatters Guest

    400,000 x 8 = 3.2Mbit per second. No PC has RS232 ports that fast.
     
  10. CWatters

    CWatters Guest

    I suspect it might not be possible to poll the port fast enough to do
    400KBytes/sec even if writtenin assembly lang. Fastest I've seen on the web
    is 250kBytes per second..
    http://www.dataq.com/news_releases/di5001nr.htm

    I would look for a PCI card to do the job.
     
  11. Oops. U'r right. there is a factor 10 missing :-s
    400kBaud is possible, but this means about 40kByte data/sec.

    Heinz
     
  12. Hal Murray

    Hal Murray Guest

    I think modern printer ports have some automatic handshaking modes.
    Can that be used with DMA? If so, how fast does it go?
     
  13. CWatters

    CWatters Guest

    I think they would manage 2MByte plus but wouldn't the effort of writing and
    debugging the software be more than you could buy a data acquisition card
    for? I guess it depends what the objective is.
     
  14. John Fields

    John Fields Guest

     
  15. Guest

    If you're just curious about PC controlled sampling and looking for
    simplicity of design and use, then the Microchip MCP3202 is a cheap, 2
    channel, 12 bit A to D and ideally suited for connecting to a PC
    parallel port.

    http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=1335&dDocName=en010532

    The chip itself is good to 100000, 12bit samples a second but there is
    no way the LPT can run this fast. The port is speed crippled by the
    internal PC ISA bus, to a rate (dependant on PC) of maybe 100k to 150k
    port changes per second.
    In practice the LPT can 'in' and 'out' serial data at about 100k bits
    per second.
    In the MCP3202 case this translates to about 8000 off, 12 bit samples,
    a second. Which is not bad!.
    Adding the complexity of a PIC and 4 bit wide LPT transfers, can get
    the rate up to about 40000, 12bit samples a second.
    In comparison, RS232 is a non starter.
     
  16. Marra

    Marra Guest

    I designed my own serial port scope a good few years ago.

    As the serial port was so slow I decided to put RAM on the acquisition
    board to capture the data very quickly.
    Once the RAM was full it would be downloaded into the PC for display.

    Depending on how much data you want to capture you could maybe use a
    similar technique.
     
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