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Thread: Lets get technical - Calling mp3car's Engineers

  1. #1
    Maximum Bitrate
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    Post Lets get technical - Calling mp3car's Engineers

    Im in process of doing some R&D on A/D converters and connectivity to PC Serial and Parrallel port.
    What I need at this moment is 12 Channels of A/D Converters to be connected to PCs Serial or Parrallel port.
    The options I have here is to use something like ADC0838 (8 Channel 8Bit A/D Converter) which outputs single Digital line that can be connected to the one of the data lines of the parallel port.
    The question then rises is, can I connect another of those converters to another dataline of the same parrallel port and read the data of both lines at the same time?
    To simplify the question let me put it this way...
    When you reading the data of the Parallel port can you read the data only of the one dataline without worring about the other lines or does it look at the LPT data line as a 8bit dataset.
    Let say we reading the data of the D7 line, which is 1101.
    Does it look at the data this way

    D0 D1 D2 D3 D4 D5 D6 D7
    0 0 0 0 0 0 0 1
    0 0 0 0 0 0 0 1
    0 0 0 0 0 0 0 0
    0 0 0 0 0 0 0 1

    or does it look at the this way
    D7
    1
    1
    0
    1
    And dosent worry about the other datalines
    So could we feed data from two seperate source two let say D7 and D4 in such a way?
    D7 D4
    1 1
    1 0
    0 1
    1 1

    As far as i understand its not possible as the parallel port looks at the data as 8bit of values comming in parrallel.
    This would be using the parallel port as 8 different serial ports??
    However i belive it could be possible to do using a software to brake the data in to an appropriate form however it will be really slow.
    Another way i could do this is use a RS-232 driver to convert TTL or CMOS level to RS-232 (one of the protocols say v.24) and then feed the data through this will get slower i believe as number of the A/D channels are increased.
    I would like to see what other engineers think regarding this matter im really off course or there is still some hope for me

    Thank.

    P.S I Hope I didnt bored most of the people here

    [ 10-04-2001: Message edited by: Fosgate ]
    Fosgate

    System Comp V3 - In progress.
    Low power MB with C7 CPU, DC-DC PSU, car ECU link, USB TV, GPS, 7" TFT, Wireless, Voice.

  2. #2
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    Data comming in on the parallel port is read 8 bits at a time. The easiest ways would be to break up the 8 bits by performing a shift on the 8 data. This would allow you to take samples from 8 chips at once. The software routines to do this would actually be very fast depending on the compiler. Doesn't the ADC0838 require a clock signal as well as the data? If it does you will need to clock the chip before reading each bit.

  3. #3
    Raw Wave Rob Withey's Avatar
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    You can mask bits in software, so it doesn't matter. Problems I would envisage using this approach are:

    1) Synchronising the data rate and data edges of the various A/Ds.

    2) Successfully decoding the data stream (sampling parallel port at correct frequency) on the PC side.

    I suspect that the data rate sync/decoding issues would kill you on this solution. If solving this problem, I would probably go for parallel bit A/Ds with a multiplexer on the port to read words in as "registers", addressed by an outgoing word on the port, latched and used to switch a MUX.

    Just my 1p worth (recession).

    Rob
    Old Systems retired due to new car
    New system at design/prototype stage on BeagleBoard.

  4. #4
    Retired Admin Aaron Cake's Avatar
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    Cool

    I did this a few years ago for a seizemograph (sp?). I used only 1 input on the parallel port and used a multiplexor to serially input the 8 bits from the ADC. Worked well, but is a little software dependent...
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  5. #5
    Variable Bitrate spud42's Avatar
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    fosgate, you are in australia arnt you? if so there is a kit at either jaycar or dick smiths to do this. it has digital i/o and analog input. multiplexes to one a/d cant remember the type at the moment. i bought one for my mp3 player as i was going to use it to display various car voltages on my lcd screen. software is a bit of an issue though. they only give yo the basics of how to get readings..
    Volvo V40 Phase 2 2002. T4 turbo upgrade.... currently no mp3 or carputer..... researching options

  6. #6
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    Yeah thanks dude...
    I rememeber looking at it few months back but i think it only had 4 channel input.
    I guess it would be useful to get hold of the schematic for the unit as a good starting point.
    The software is not really a problem ...
    As long as you know C or ASM then it can be easly implemented.
    Fosgate

    System Comp V3 - In progress.
    Low power MB with C7 CPU, DC-DC PSU, car ECU link, USB TV, GPS, 7" TFT, Wireless, Voice.

  7. #7
    Variable Bitrate spud42's Avatar
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    cheers dude... got it at home... am going to use it on mine... will bring it in tomorrow if i can find it... i think the one i got has 10 inputs for analog..... cost about $45 AUD .... if you need the circuit give me a fax number .........
    Volvo V40 Phase 2 2002. T4 turbo upgrade.... currently no mp3 or carputer..... researching options

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