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RS485 Half duplex DC power line communication using modulation

Rahul Bhandari
Prodigy 30 points

Other Parts Discussed in Thread: SN65HVD63, SN65HVD72, SN65HVD82

A Power line communication Solution which can work on 115200 Baud Rate with RS485 interface as input. In output 12V DC power with load of 350mA.

I have consider  http://www.ti.com/lit/ug/tidu993/tidu993.pdf

But this needs software changes Manchester encoding of the signal which i do not want to go with, so looking for a solution with hardware modulation.

  • 0
    TI__Guru 62920 points
    Hi Rahul,

    A Manchester encoder could be implemented in hardware by using an XOR gate to combine the data line with a synchronous clock line. If you didn't want to do that, another approach might be to move away from RS-485 and use a different signaling type like on-off keying at a high-frequency carrier (which would more easily pass over the AC-coupling capacitance needed for combining power and data lines). SN65HVD63 would be an example of a modem device that could take in single-ended logic signals and convert them to high-frequency modulated signals for transmission over a cable.

    Max
  • 0 in reply to Miguel Robertson
    Prodigy 30 points

    Max ,

              Thanks for the suggestion, still can you suggest similar kind of IC like SN65HVD63 which can take RS485 signal as input. Actually this RS485 interface is implemented on main board which uses 4 wire for transmission and I am making a daughter board which can make it work with 2 wires and I cant change hardware or software bcoz then I have to go to certifications again. So please suggest some solution

    Rahul.   

  • 0 in reply to Rahul Bhandari
    TI__Guru 62920 points
    Hi Rahul,

    SN65HVD63 could directly interface to an RS-485 transceiver like SN65HVD72 or SN65HVD82 (depending on which VCC level is needed) via the TXIN, RXOUT, and DIR pins. That seems like the most straightforward solution. The other option is to make something like an RS-485 repeater (e.g., by adapting this reference design: www.ti.com/.../TIDA-01365) and introducing a discrete Manchester encoder or other simple modulation scheme in order to increase the signaling rate.

    Max
  • 0 in reply to Miguel Robertson
    Prodigy 30 points

    Max,

         I do not have UART Signal accessible, we just have RS485 pair. So I cant directly connect SN65VD63 in the design.

    The 2nd suggestion seems to solve my problem but in it has 2 transceivers it will increase the cost.

    I will work on 2nd suggestion and see how to reduce cost.

    Thank you

    Rahul.       

  • 0 in reply to Rahul Bhandari
    TI__Guru 62920 points
    Rahul,

    Ok, sounds good. Just to clarify, the first suggestion was to use both an RS-485 transceiver (to convert the differential signals to single-ended logic signals) and the SN65HVD63 (to translate those logic signals into an RF OOK signal).

    Max