Enhance Palleral Data Transmit with Long Distance Design

Discussion in 'Embedded Systems and Microcontrollers' started by bctang, Nov 2, 2007.

  1. bctang

    Thread Starter Member

    Sep 5, 2004
    26
    0
    Hi,

    I'm still new on this forum.

    I'm trying to transmit 8-bits data from A location to B location which is 20 meters long. Do i need to do any enhancement design on both A and B location so the data can able to transmit more stable condition?

    I'm using 8052 MCU. The MCU port will connected it to 74HC573 to pull out the 8-bits data at location-A then transmint the data to location-B (location-B most of that is TTL device, the location-A 8-bits data will link it to 74HC259 and some other logic device. The HC259 output will be connected to x8 LEDs). Between location A and B will be very long distance, 20 Meter. I just plan to use parallel method to transmit the data. I know serial method can solve this problem. I just want to take experience on it. Hope can use parallel method to solve it.

    I already did the design but is on testing board. But haven't test it in long distance.
    1) How to solve the transmission line effects?
    2) the switching rate is not so frequent. If can turn ON the output LED within 1sec will be nice. Is it possible to do that?
    3) driver impedance - using normal TTL driver HC573 (data output driver), HC259(input device), 4077, HC153, HC00 and so on..
    5) Normal parallel port 25-pin connector and cable.

    What other issue i have to consider? For your experience this design able to achieve? Please advice...

    Thank you.
     
  2. GS3

    Senior Member

    Sep 21, 2007
    408
    35
    I am not sure what your ultimate objective is but, in general terms, just using a parallel data cable that long is not a good idea and it is better to use a serial transmission system like RS232 or RS422. If I had to use parallel transmission I would at least design a robust interface with optoisolators.

    If you MUST use direct TTL levels make sure you use low impedances and plenty of precaution, noise suppression, shielding, etc. Even then you might run into problems.
     
  3. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    I don't believe that you can get any good results with TTL signals transmitted over 20 meters in any kind of cabling. 2 meters is pushing it. GS3's alternatives above for using serial technologies are good. It it has to remain parallel, you will need to find a line driver that uses differential signaling on twisted pairs. That method is good to about 100 meters, but expensive - especially compared to RS-232.
     
  4. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    .... Concurrent posting .... This just reinforces what beenthere has already stated.

    As GS3 has already indicated, using parallel transmission for your very slow data rate is a very inefficient method. Your application is must better suited to the use of serial data transmission.

    Since you seem intent on going forward with your parallel implementation purely on the ground of gaining experience in long run parallel data transmission techniques then you should heed the suggestions that GS3 has outlined. In particular the use of optoisolators will be beneficial.

    To improve your chances of maintaining data integrity over the 20 meter run you propose, you should strongly consider the use of differential signals through the cable. This means of course that your cable will need twice as many conductors as you have signal lines.

    You will need to convert from single-ended signals to differential signals on the end where your data originates and then convert back to single-ended from differential on the data reception end.

    You did not specifically mention whether you intend to send data in both directions over this parallel data link. If that is the case then your problem is compounded by the need to decide whether you want full-duplex or half-duplex data flow. These same decsision would need to be made whether you select a serial or parallel data transmission. It is just that double up on a few serial lines has a much smaller impact than doubling up on say 8 data lines plus any control lines you plan to support.

    By now it should begin to be clear that serial data transmission has many advantages over parallel data transmission.

    Good Luck,
    hgmjr
     
  5. bctang

    Thread Starter Member

    Sep 5, 2004
    26
    0
    Hi, Members

    Thank for you all advice and sharing the knowladge.

    If go for GS3 method. I think it will costly solution. Am i rite?

    hgmjr:
    Could you please explain more detail about this because i'm couldn't understand.

    hgmjr:
    There are 3 pack of data will be transmit out from the A side. The last 1 bit will be the receive data from B side.
    - 8 bits data pack which is 1byte data will transmit it in parallel. (transmit)
    - 3 bits data pack (transmit)
    - 2 bits data pack (transmit)
    - 1 bit data (receive)
    Total 13 data out and 1 data in.

    So, now i'm thinking..If we try to use the ribbon cable and in between the data will be comman ground. :rolleyes:

    Please advice, and kindly share the experience and knowlagde.

    Thank You.
     
  6. GS3

    Senior Member

    Sep 21, 2007
    408
    35
  7. hgmjr

    Moderator

    Jan 28, 2005
    9,030
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    As an alternate to the devices suggested by GS3, here are a couple of ICs that when used in pairs will support 4-lines of data.

    On the out-bound end of your data link you would need four SN65LBC172N to convert the 13 lines from single-ended to differential mode and one SN65LBC175AN to handle the one line in-bound to convert the differential signal back to single ended.

    On the opposite end of the data link you would need four SN65LBC175A ICs to convert the 13 differential data pairs back to single-ended mode and one SN65LBC172A to convert the one data signal being transmitted back from single-ended to differential.

    Datasheets for these two devices can be found at www.ti.com.

    hgmjr
     
  8. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
    6
    Would a separate RG179/U coax for each bit do the trick? You could lace them into a bundle as if they were telecom cable.
     
  9. chesart1

    Senior Member

    Jan 23, 2006
    269
    1
    [To improve your chances of maintaining data integrity over the 20 meter run you propose, you should strongly consider the use of differential signals through the cable. This means of course that your cable will need twice as many conductors as you have signal lines.
    You will need to convert from single-ended signals to differential signals on the end where your data originates and then convert back to single-ended from differential on the data reception end. ]

    Look up the RS422 standard for differential signals. There are ICs that convert RS232 to RS 422. The question is: Will the receiver of the data support RS422.


    ARC's RS422 Tutorial & info on converters
     
  10. bctang

    Thread Starter Member

    Sep 5, 2004
    26
    0
    Hi, Dear Members..

    Thank for your all advice. The parallel-serial converter would be abit expensive for me and i couldn't find it in local. But i learn new thing. Thank again.

    Now i'm trying to use the ribbon method. Hope it can work. If not, i will try to switch it to serial. Hope you all can help me.

    Thank You.
     
  11. GS3

    Senior Member

    Sep 21, 2007
    408
    35
    The meters of cable are going to cost you much more than converting to serial.
     
  12. bctang

    Thread Starter Member

    Sep 5, 2004
    26
    0
    Hi Dear All,

    Thank for your all advice and shared the knowledge.

    Last week i just done the testing. It working fine.
    I'm using ribbon cable to carry my data along 24 feets and i'm using low-level logic signal as my data signal.
    The transmision data rate is around 1Kbps.

    I'm not sure that is the long term solution but i'm be observed one week it working very well. Alot of people don't advice to use parallel data for long distance transmission. I will try to switch the design to serial 485.

    Thank again...
     
  13. jonhults

    New Member

    Apr 7, 2009
    1
    0

    Oh you will be surprised at how much the meters (cable) will cost you.
    Good Luck
     
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