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RS232 - RS422 CONVERTER

Discussion in 'General Electronics Discussion' started by HellasTechn, May 15, 2018.

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  1. HellasTechn

    HellasTechn

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    Apr 14, 2013
    HELLO !

    I am looking for some converter that can convert rs232 to rs422 and at the same time rs422 back to rs232. In other words i need to connect the converter to my laptops rs232 serial port and exchange data between an rs422 device. Probably something that can be powered from a 5v usb port so that i dont need to carry an external power adapter and costs like 10-20 USD ?

    P.S. Yes my laptop does have a serial port :)

    Thank you !
     
  2. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    Have you tried Google or another search engine? I get lots of hits. Although cost is typically quite a bit more than your stated goal. These adapters are usually not USB powered.
    Why not use a USB <> RS422 adapter? That solves at the same time your second issue, the power suply via USB.
     
  3. HellasTechn

    HellasTechn

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    Apr 14, 2013
    Because i work on old GPS receivers and compasses that communicate via RS422 while i practice ways to interface them with microcontrollers that use rs232 (either ttl or cmos voltage levels).
    Though your idea is not that bad.

    One other alternative i see is for me to build such a converter with a max232 and a ds8921 chip. I could combine the typical circuit diagrams of these chips and power them with 5V from a usb.

    That should be simple enough. Though i was really hoping to avoid that.
     
  4. AnalogKid

    AnalogKid

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  5. Minder

    Minder

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    The one in the second link can be had for 1/4 the price ebay 152979237575
    I have used these in the past and work well, no separate power required.
    M.
     
  6. AnalogKid

    AnalogKid

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  7. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    Jassu Constantine.

    You led me on the wrong path by what I think is a misunderstanding on your side.
    RS232 is a standard that operates on comparatively high voltage levels (+- 15 V). RS232 can be and is typically used to communicate via a UART protocol.

    When you mention TTL or CMOS levels, you mean the UART interface of the microcontroller. This is not RS232! You can directly create an RS422 interface to the UART port of a microcontroller. E.g. Maxim offers few easy to use componnets that can be powered from the microcontroller's 5 V or 3.3 V supply, see here. These chips are not expensive and easy to handle. The question is whether you use full duplex (separate TxD and RxD lines) or half duplex (shared TxD/RxD line). You'll have to chose the appropriate chip and you need to make teh software fit for handling simultaneous Tx/Rx (full duplex) or alternating Tx/Rx (half duplex).
     
    HellasTechn likes this.
  8. Minder

    Minder

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    All you need to do is go to Any ebay listing and substitute the 12 digit number with the the one in the listing URL and delete everything after it.
    I use these for equipment that has RS485 modbus inputs from my laptop COM port.
    M.
     
    Last edited: May 15, 2018
  9. AnalogKid

    AnalogKid

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    Jun 10, 2015
    I know that part. But I can't seem to hit the right combination of words to have that part come up in a general search. For example, changing from "RS232-RS422" to "RS232 to RS422" got me closer, but your part still did not come up. Not exactly the end of the world.

    ak
     
  10. Minder

    Minder

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    Odd? I just entered RS232 RS485 in my search and it is at the top.
    I guess RS485 makes the difference.;)
    M.
     
    HellasTechn likes this.
  11. HellasTechn

    HellasTechn

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    Okay i think i know now what the confusion is. I should have explained better.

    I need the converter to to enable my laptop to receive rs422 and also transmit rs422 to devices such as GPS and compass.
    Why do i need that ? because i try to figure out ways to interface microcontroller with the above rs422 devices.
    The converter i am looking for is not to be used between the rs422 devices and the microcontrollers but between the rs422 devices and my laptop.
     
  12. HellasTechn

    HellasTechn

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    Apr 14, 2013
    Since my knowledge about serial communication is very limited, the next question that pops into my mind is this:
    is the rs485 standard compatible with the rs422 ? Can i use and wire the above converter as i would with an rs232 to rs422 ?

    I searched and found this:
    http://www.ti.com/lit/an/slla070d/slla070d.pdf

    Paragraph 2 (if i remember correctly) states that rs422 and rs485 appear to be similar but they are distinct and interchangeability
    is determined by the bus architecture.
     
  13. AnalogKid

    AnalogKid

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    Jun 10, 2015
    For point-to-point connections (non-bused), 422 and 485 are essentially identical. 422 allows multiple receivers on one line, but only one driver. 485 allows multiple drivers and receivers on one line.

    ak
     
    HellasTechn likes this.
  14. HellasTechn

    HellasTechn

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    Apr 14, 2013
    Thank you all !!!
     
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