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    RS485 question

    This relates to thermostats. Can I just get a RS485 to RS232 converter, connect that to my pc and then read and control the thermostats that are connected to my JDS Stargate RS485 bus? Could it be that simple?

    Matt

    #2
    I don't think so, unless you can configure addresses and the Stargate thing can take care of the addressing. Otherwise you CAN do that, so long as you use 1 serial port per device and use 422 (5 wire). If you want to use that, What I've done is use a piece of ethernet, then you can use one pair of wires for TX, 1 for RX, 1 for GND, 1 for power (use something a bit higher then you need as you will get loss depending on the distance run...so, you may want to measure the voltage at the end before wiring in your electrical device to make sure the voltage levels are high enough).

    There are a LOT of 485 protocals out there, so using the right one is important.

    --Dan
    Tasker, to a person who does Homeautomation...is like walking up to a Crack Treatment facility with a truck full of 3lb bags of crack. Then for each person that walks in and out smack them in the face with an open bag.

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      #3
      I know very little about the RS485 protocol. That was the main reason for posting the ??

      Comment


        #4
        well, 422 is a voltage difference to 232.

        422 allows for (at low rates) signals to be sent to close to a mile. It is differential (hence 5 wires needed).

        485 is most of 422, with a twist. It allows for 3 wire or 5 wire. Which means that if you are using 5 wire 485, it IS 422. If you are using 3 wire, then it is kind of 422 (in that it will be differential).

        The big difference is that with 3 or 5 wire, you need a master. That is your Stargate thing. Depending on the protocol being used, there is either a token ring type of setup, or a master/slave. The Master slave means that the master will ask each device what it's current status is. Token ring means each device can contain the "token" and thus when it has the token, it is allowed to "talk".

        My guess is the stargate does a master slave type of setup. Now, with any 485, there is an address scheme being used. ALL the devices hears everyone's address/command, however if the address is not "my" address, it's ignored. JUST like X10. ALL devices plugged in, hear all commands, but if the address is NOT mine, then ignore it.

        So, unless you have a way of buying a 232 to 485 device that handles the address conversion, which should be specified by the stargate thing, then it won't work. BUT if you want to dedicate a RS232 port to each device, then use a 232 to 422, then a 422 to 232 on each device, you can get 422 to work without any extra software or special settings.

        --Dan
        Tasker, to a person who does Homeautomation...is like walking up to a Crack Treatment facility with a truck full of 3lb bags of crack. Then for each person that walks in and out smack them in the face with an open bag.

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