Questions about rs232 range extension

Discussion in 'General Electronics Chat' started by mamech, Apr 13, 2011.

  1. mamech

    Thread Starter Member

    Nov 3, 2010

    I am quiet new in field of rs232, so I want to ask about the achievability of what I will say.

    I have read that according to standard of rs232, the max range is 15m, and the max speed @ 12m is 20kbps.

    My questions are the following:
    1-Can I make baudrate lower than 20kbps, so I can get more range? What the range could be if I used 9600kbps or 2400 kbps?

    2-If I used twisted pair to transmit rs232, will this give a boost in range (because noise in eleminated)?

    3-Can using rs232 repeaters double it max range?

    4-In case of having a cable of 100m length(I am supposing here that the above mentioned scenarios can make me send with rs232 up to 100m) transmitting rs232 data , will be signal termination important? And will it be done using the same method as rs485 networks?(I mean that one searches for cable impedance and select a resistor that has the same impedance, etc..)

  2. gerty

    AAC Fanatic!

    Aug 30, 2007
    I have used rs232 at a distance of approximately 100 feet. We had to slow the rate down to 9600 for it to be consistant.
    100 meters may be out of your reach with rs232. If you are stuck with rs232, they make convertors that will take the rs232 signal and convert it to rs485 to travel the distance then you'll have to convert it back to rs232.
  3. SgtWookie


    Jul 17, 2007
    If possible, you would be far better off to go to Ethernet.
  4. mamech

    Thread Starter Member

    Nov 3, 2010
    Yes, I know that both Ethernet and RS485 can afford a far better range, but I am still asking about the above mentioned questions, in order to know the limitations of rs232. Knowing the limitations of a protocol makes you know when you should use it and when you should not.

    Another thing to mention, I need to use either RS232 or RS485 in an application in which a lot of microcontrollers (nodes) should be networked with each other. So for minimizing cost, I think that rs232 is better as I will not use any converters to interconnect microcontrollers, but still the range represents a problem.

    Can anyone help me by answering the above mentioned questions?
  5. russ_hensel

    Distinguished Member

    Jan 11, 2009
    And from wikipedia:

    Maximum cable segment length

    According to the ANSI/TIA/EIA standard for category 5e cable, (TIA/EIA 568-5-A[5]) the maximum length for a cable segment is 100 meters (328 feet). If longer runs are required, the use of active hardware such as a repeater, or a switch, is necessary.[6] [7] The specifications for 10baseT networking specify a 100 metre length between active devices. This allows for 90 metres of fixed cabling, two connectors and two patch leads of 5 metres, one at each end. In practice longer lengths are possible. (See Ethernet over twisted pair which states that 150 m is often considered to be the maximum working length.) Experiments show that a full 305 metre drum of cable is well above the practical limit, but that reliable transmission with 200 m is often possible.
  6. THE_RB

    AAC Fanatic!

    Feb 11, 2008
    But that 100 feet limitation is at a very high datarate!

    I've seen industrial RS232 run hundreds of metres with no problems, at low baudrates like 1200 baud.

    The OP seems to be wanting to use the microcontrollers output pin to drive the cable direct, and that pin should be a low impedance push pull driver that is ok to source/sink 20mA or 25mA.

    That should be an excellent cable driver, and the micro will probably have a schmidt input pin to receive the data. I wouldn't be surprised if you can easily get 100 or 200 metres at 20kbps with a standard twisted cable.

    I have a machine here running RS232 over 20 metres at 57kbps, and it only has the PC serial port driving it. A push-pull 20mA output should outperform that.
    mamech likes this.
  7. mamech

    Thread Starter Member

    Nov 3, 2010
    Thanks for useful information.

    "I've seen industrial RS232 run hundreds of metres with no problems, at low baudrates like 1200 baud."

    Does this industrial RS232 have any thing different from the normal RS232?

    "I wouldn't be surprised if you can easily get 100 or 200 metres at 20kbps with a standard twisted cable."

    Will a twisted cable make a difference when used with RS232 ?There is some person told me that twisted pairs are only useful when dealing with differential voltage.

    "A push-pull 20mA output should outperform that. "
    Sorry to ask, but how I can do such push-pull 20mA output ?

  8. THE_RB

    AAC Fanatic!

    Feb 11, 2008
    1. No the "industrial" meant the environment. It was standard RS232.

    2. The twisted pair cable will pickup less noise. Gnerally you woul duse twisted pair cable because you can buy long lengths of CAT5 cable or telephone 2pair cable dirt cheap.

    3. In post #4 you said "a lot of microcontrollers" and "low cost" so you can just use the microcontroller TX and RX pins to drive the wiring. The micro's TX pin is a push-pull output.

    Why not buy a $8 telephone extension cable 50 metre length etc and connect it to your 2 micros and do some testing? :)