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Raspberry Pi Forum How  to read data from RS485 port of a device using raspberry pi
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How  to read data from RS485 port of a device using raspberry pi

profravisaxena
profravisaxena over 9 years ago

I need to get data from RS485 port of a transducer in to raspberry pi to connect it to IOT. Any suggestions

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  • balearicdynamics
    0 balearicdynamics over 9 years ago

    Hello Ravi,

     

    PI3 has a good support for the UART serial connection. If I am not wrong the difference between the RS232 and RS485 is that the second is based on differential currents on the signals to compensate / avoid some kind of external interferences and work with higher currents than the 5V of the 232. What you need I think it is a small circuit to convert the 485 industrial serial connection to the TTL level of the UART in the PI, as well as you should do if you will use a 232, with a Max chip (just for an example).

    Accordingly with these notes:

    serial - Difference between UART and RS232? - Electrical Engineering Stack Exchange

     

    In my opinion, also to avoid to spend a lot of time to make a conversion circuit by yourself, FTDI already provide USB to 485 adapters together with the USB to 232 based on their FTDI232 and FTDI485 chips. You can get the chip specifications to integrate the conversion circuit in your own project or just buy an adapter (at least to test the prototyping phase and develop proper software on the Raspberry PI).

    Below are the links:

     

    https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&sqi=2&ved=0ahUKEwj4u-ey-7DNAhVKL8AKHU7EB-…

    https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=4&cad=rja&uact=8&sqi=2&ved=0ahUKEwj4u-ey-7DNAhVKL8AKHU7EB-… 

    The FTDI converter datasheet (pdf) : http://www.ftdichip.com/Support/Documents/DataSheets/Cables/DS_USB_RS485_PCB.pdf

     

    Depending on the quality and current range of your RS485 source I suggest to evaluate to eventually optoisolate the signals.

     

    Enrico

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  • rew
    0 rew over 9 years ago

    Hi Ravi,

    I sell a board that is meant to do DMX. DMX works based on RS485. I'd like to know if we can hack it to work with your RS485 sensor.

    I was going to say I would send you a board for free. But the most practical thing is that you order the cheapest item from my shop so that I have your contact details. So its "almost free".

    I'll be glad to work with you attempting to get it to work. For example, in your case it might be better for you if we leave out the bulky DMX connectors. So that will be the first thing we'll need to discuss. How does that sound?

     

    P.S. The "uart" on the pi3 isn't that good. The processor has two UARTs and one of them is "reasonable" the other one is "mediocre". And the better one was assigned to bluetooth... You can "steal" it back, so that the better uart now goes to the GPIO pins like on the PI2 and earlier models.

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  • rsc
    0 rsc over 9 years ago

    SparkFun also sells some RS485 breakout boards for about $10

    https://www.sparkfun.com/products/10124

    Scott

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  • profravisaxena
    0 profravisaxena over 9 years ago in reply to rew

    Dear Roger

    Thanks for offering your support . Pls send me the link of your website so that i can see DMX card and other products. Also like to know whether  DMX card can be shipped to India.

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  • rew
    0 rew over 9 years ago in reply to profravisaxena

    My shop is at: https://www.bitwizard.nl/shop/

    When ordering you can add a comment. If that fails (some people can't find it), send an Email to info@ mydomain. "Ribbon Cable, 16 Way, 10cm" is probably the cheapest item you can find.

    The shop will ask you for your email address, so that I can contact you about the connectors.

    We use regular mail services so if you can get mail, you can get our boards. :-)

    If you think "tracked shipping" is advisable (in your country because mail might be stolen) you should select tracked shipping. This would work through "DHL Parcel". Alas that is more expensive. We don't make any money on the "and handling", we just charge what the post service/DHL charges us.

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