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RS485 to TTL Circuit Needed (can pay)

Discussion in 'Electronic Design' started by Fatima Peredo, Oct 14, 2003.

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  1. Hi,

    I need a simple device based on a PIC that will connect to an RS485
    network and output 20 TTL compatible digital outputs. I know it's
    simple and I could probably design one myself, but I'm sure this must
    have been done before. I've searched the Internet but I only seem to
    find RS485 boards that also have analog inputs or other features added
    on I don't want or need.

    If someone knows of such a product, I'd be very interested. If not, I'd
    be willing to pay a fee to someone to design one (or modify an existing
    one they know about) for me.

    Thanks in advance.
  2. Phil Hobbs

    Phil Hobbs Guest

    This isn't a very specific description. What sort of RS-485 network,
    using what protocol, and what do you want the digital outputs to do?
    Twenty resistors connected to +5V would satisfy the spec you've written.


    Phil Hobbs
  3. jake

    jake Guest

    I have a similar need but mine is to read analog signals via half-duplex
    RS485. The PIC16c773 looks like it would fit the bill nicely, 12-bit ADC
    and few external components needed. I'd want to send out an ASCII request
    to a specific RS485 address, i.e. "GetData 137",and have the six readings
    come back in one CSV string (137, ad0, ad1, ad2, ad3, ad4, ad5). I've never
    done PIC before so was considering using one of the Basic 'compilers' to
    program it, I thought Basic would be sufficient considering this is not a
    very demanding app. Any thoughts, advice, bids (via email)?

    thx, jake
  4. I haven't decided on a protocol yet, but the devices will be connected to
    an embedded PC (I also haven't picked which one yet). There will be 18-20
    of these devices connected to a single RS485 line and of course each one
    need to have its own "address" so I can send data to a specific device.

    The 20 digital outputs are going to a couple of circuits which will do
    actions depending on the data. Two of these are comparators and the other
    two are counters. They use this digital data to make a decision on when to
    activate another devide.

    I already have these other circuits which require the 20 bits of information
    as inputs. Each of these circuits (devices) is separate, so using a single
    board with say 60 outputs (20 to each of three) is not practical.

    I have been to various RS485 sites and have seen several products but
    none that would do what I want specifically. As mentioned previously,
    I don't need A/D, counters or timers so purchasing an RS485 I/O board
    with these features is a waste of money.

  5. Phil Hobbs

    Phil Hobbs Guest

    Unless you're going to be needing a whole heap of these things, you'll
    be much better off with a purchased solution, no matter how many bells
    and whistles it has. Designing and building a one-off will cost
    thousands of dollars if you pay someone else to do it. OTOH, you could
    do it yourself, save a lot of money, and learn some useful skills.


    Phil Hobbs
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