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send data over 5km wire length possible?

VT
Genius 3300 points

I have digital data over uart, which need to be sent over 5km wire length. Digital data I can cnvert to any protocol like spi, i2c or any other or even single wire.
RS485 has limitation for 5Km. 

No place for repeators in between

how can i send data?

I think  4-20mA transmitter/receiver which can do this? Any soluion available for this?

  • 0
    Guru 140200 points
    Ho Vindhyachai,

    this mainly depends on the baud rate. High baud rates need the characteristic impedance matching of cable to overcome the cable capacitance limitations.

    What is your baud rate?

    Kai
  • 0 in reply to kai klaas69
    TI__Mastermind 25705 points
    Vindhyachai,

    5km is not a short distance. I doubt any single-ended signaling can support it. spi and i2c are more intended for board level communication. RS-485 might be an option, but as Kai mentioned, there are some tricks to be taken care of. Please share more information and I will follow up.

    Regards,
    Hao
  • 0 in reply to Hao L
    Genius 3300 points
    Hi,

    Baud rate is low. Like 10 bytes of data per second.

    can 4-20mA transmitter on one end & receiver on other end be an option? i am particularly interestred in this, as with this any noise will not have any effect on signal.

    if it not suited, Any other method suitable for this?
  • 0 in reply to VT
    Guru 284840 points
    A current loop at 120 bauds sounds OK.

    Check the resistance of 10 km of cable; if the voltage drop is too high, the driver might need a higher supply voltage.
  • 0 in reply to VT
    Guru 140200 points

    Hi Vindhyachal,

    I would do it this way:

    5km_opto.zip

    To improve the noise rejection I would use a +/-10V square wave output signal with a baud rate of 120Baud, as Clemens already suggested. The 1k resistance (R1) limits the current in the current loop to about +/-10mA.

    On the receiver side you see the opto CNY17-3. D1 protects the opto from negative input voltages. For D1 a simple 1N4002 can be used.

    The ripple on the loop current comes from the cable reflections and is quite normal.

    A 0.25qmm cable is assumed.

    Of course, both ends of the cable should have some additional ESD, surge and burst protection.

    Kai