Create Bus For microcontrollers

Discussion in 'The Projects Forum' started by danics, May 10, 2010.

  1. danics

    Thread Starter New Member

    Feb 27, 2010
    Hi all!

    i m a beginner in Microcontroller and i want to know how can i create a Bus system for connect 1040 AVR or PIC microcontrollers to my Arm board whats your idea , you think i must use RS485 or another system please guide me?

    my big project is control of opening and closing 1040 doors that every door have a serial number and my user enter door number and his password to open his door.what system is better here, my distance from doors is at most 20 to 30 meters thanks a lot.
  2. Papabravo


    Feb 24, 2006
    There is nothing like running a marathon before learning to crawl and walk. There are few if any low cost networking technologies that will allow the connection of 1040 nodes on a bus and allow a coverage in the neighborhood of 30 meters.

    First problem is node impedance. Question: if each node has an impedance of say 20 kilohms, then what is the impedance of 1040 of those nodes in parallel?

    How fast do you want the bits to go flying back and forth? Why do I ask? Because the faster the data rate the more careful you will need to be about the distributed capacitance of your cable system.

    How will the nodes be powered? If they are powered separately then you have to watch common mode voltage differences to make sure a one here is not a zero there. If they are powered from a power pair on the network cable what size wire will you have and what size power supply(ies?) will you have.

    To solve these problems will take considerable engineering skill. Are you sure you are up to it?
  3. Markd77

    Senior Member

    Sep 7, 2009
    Where has 1040 doors in that range? A prison?
  4. retched

    AAC Fanatic!

    Dec 5, 2009
    I think he means the distance between doors. Maybe not.

    I dont know why you would want to use 1040 uCs in the first place. Why not just reed switches, and RF. Just like house alarms. No need to reinvent the wheel.

    You will need an encoder that is capable of 1040 addresses, the ones I know of are capable of 1024. going up above 1024 may be expensive.

    But I would use a wireless solution. But the control room or main reciever at the center of the neighborhood and you have a radius to transmit to.

    You will then have a 1024 bit word that is either 1 or 0 for open or closed.
    1010101000010000000000000101101111111110000000000000000000001010100 etc.

    First number is door 1, 2nd number is door 2, 766th number is door 766, etc...

    Is this a design only task, or are you considering building this?

    Usually professors give these types of assignments to get students thinking outside of the 1024 range.
  5. t06afre

    AAC Fanatic!

    May 11, 2009
    Hi Danics
    What are you trying to build? If you provide more details it would be more easy to help you.
  6. danics

    Thread Starter New Member

    Feb 27, 2010
    Hi every body and thanks a lot,
    Prison :)!!!!

    i m sorry that i was late to answer, my project is control of deposit safe boxes in Bank, so my distance is at most 30 meters. i want to connect doors to my access control with low cost wiring and i cant use of wireless system too.i have a option that i don't use of Microcontrolers for doors too but i want monitor opening and closing time of the doors, if you have another suggestion please tell me, another problem is maintenance of system in the future. thanks a lot.
    Last edited: May 12, 2010
  7. retched

    AAC Fanatic!

    Dec 5, 2009
    You just need a switch on each door, then multiplex to the uC.

    The uC, can poll all of the switches, and check when they are closed (NO switch and door is open)