RS232 to RS485 with 555 ICs

Discussion in 'Embedded Systems and Microcontrollers' started by anhnha, Apr 19, 2012.

  1. anhnha

    Thread Starter Active Member

    Apr 19, 2012
    773
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    Hi,
    Can you give a RS232 to RS485 and vice versa using 555 IC to control RE and DE of Max485?I have try to connect but not work?
     
  2. chrisw1990

    Active Member

    Oct 22, 2011
    543
    41
    are you using RS232 voltages? might be easier to convert 232>UART>485.
     
  3. anhnha

    Thread Starter Active Member

    Apr 19, 2012
    773
    45
    Yes I want to communicate between 2 computers but one is 100m from other.I have to circuit
    -rs232 to rs485
    -rs485 to rs232
    and i have wire it in breadboad but it is not work.Could you give me the schematic to do it?
     
  4. MrChips

    Moderator

    Oct 2, 2009
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  5. panic mode

    Senior Member

    Oct 10, 2011
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  6. Felo

    Member

    Feb 20, 2012
    91
    13
    This is what you need, this not "real" RS485, it is an implementation that I've made wich is in operation now in a multidrop network of devices, made it 2 years ago and it has not gave me any problem YET.

    IC1 and 4 =SN75176
    IC3 = MAX232

    Use this way PC>>This circuit>>Line>>This circuit Nº2>>PC Nº2

    Remember to use anti-reflection resistors on both ends, This circuit only carry Tx and Rx, no HWD protocol, can overcome this in end PC or some gadget software, use UTP or STP (better) 4 pins are used.

    This circuit as it is, can be greately improved, for all you people out there feel free to do so, I would just like to recive your final improvements if you choose to do so.

    Happy Networking
     
  7. panic mode

    Senior Member

    Oct 10, 2011
    1,320
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    this is not readable, could you zoom in and at least turn off the grid?
     
  8. Felo

    Member

    Feb 20, 2012
    91
    13
    Whoaa.... my bad, one schematic coming up!
     
  9. Felo

    Member

    Feb 20, 2012
    91
    13
    Here it is, thank for the heads up Panic....
     
  10. anhnha

    Thread Starter Active Member

    Apr 19, 2012
    773
    45
    Thanks.I had do the circuit like that.But I wire up in breadboard it is not work.In my project I need to communicate between computer(COMM PORT) and micro.But now I want to check 2 circuits that I had wire in breadboard:
    -the first breadboard for RS232 to RS485
    -the second breadboard for RS485 to RS232
    in reality, I need 2 computers to communicate but now have only one therefore I used TX pin of comm port to transmit and also used RX of this port to receive data.
    Because I only used on computer thus I had connect TX of comm port to 232 input of one breadboard and RX of comm port to 232 output of the other breardboard.And then I used the program i posted above to transmit and receive data from comm port.But when I am not use 5 Voltage connected to ICs and I supprised due to is read from comm port is exact but when power is connected then it is not work.At first I think that it receiced data may be TX and RX is connected to each other but when i used ohm meter to measure the resistance between TX and RX, i received the value is very large and this mean it is not connected.I am confused why it is not connected but i can received data and when power is connnected it is not work.
    I have checked all connected in breadboard, all of them are good.Would you give me how to solved it,i have wire up the circuit in breadboard many times but all are the same.Finally I can not to transmit between two computer.Will i need add something in this circuit in reality?Are there anything wrong in my schematic?
    would you help me check it.I have attach my file in this.
     
  11. t06afre

    AAC Fanatic!

    May 11, 2009
    5,939
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    What are the 555 circuits doing in all this. I also suggest that you replace the half duplex RS485 chip (MAX487) with full duplex version (MAX488).
    Then just use this concept RS232->MAX232->MAX488------MAX488->MAX232->RS232
     
  12. t06afre

    AAC Fanatic!

    May 11, 2009
    5,939
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    @anhnha
    You have several threads related to the topic in this thread.
    http://forum.allaboutcircuits.com/showthread.php?t=69169
    http://forum.allaboutcircuits.com/showthread.php?t=69148
    http://forum.allaboutcircuits.com/showthread.php?t=69119
    http://forum.allaboutcircuits.com/showthread.php?t=69084
    Quite hard to follow. And also please answer the questions then asked. Do not just start a thread then you do not like the answers or questions asked. I have looked at your schematics and find it hard to see the functions of the 555. What is the purpose of doing this.
     
  13. anhnha

    Thread Starter Active Member

    Apr 19, 2012
    773
    45
    Thanks for your reminder.
    I have found this:http://www.bb-elec.com/bb-elec/literature/485ptbr-3903ds.pdf
    and I want to do it but not succeed.I used 555 to control RE and DE of MAX485, i aslo built two circuits like in datasheet above in breadboard.when i run it i received data even when power not connected.Would you help me do i need anything else in the converter operate.
    and below is the circuit I used.
     
  14. anhnha

    Thread Starter Active Member

    Apr 19, 2012
    773
    45
    Thanks.
    I used 555 to control DE and RE of max485.I have found it in this:http://www.bb-elec.com/bb-elec/literature/485ptbr-3903ds.pdf
    Yes.I think it is good but now i want to simulate half duplex first.
    Yes.I used it.I made 2 breadboard
    -RS232->MAX232->MAX485
    -MAX485->MAX232->RS232
    But it is not successed to me.I tested but used ONLY one comm port.It means that i used TX of comm port to transmit and RX to receiver in the same computer.Every component I checked and it is worked but when i used schematic above to test i received data even when power is not available and
    GND of comm port is removed.At first i think it is my error, may be the TX and RX is connected by accident but not.when I used ohmmeter to measure the resistance between TX and RX it is very big.I think if it is connected then the value is have 0 ohm.And have another problem that i can not to understand is that why TX pin of comm port is always negative voltage.As far as i know it is 232 standard thus it have to have the value between -25V to +25V.As for my program it is good.I tested it by connected TX and RX directly and it work.
    Would suggest me how I verify it.I took a long time to rewire and check it but not effect.
     
  15. MrChips

    Moderator

    Oct 2, 2009
    12,436
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    You have three threads going on the same topic. Try and keep the discussion on one thread only. A mod is going to come along and shut down two threads.
     
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