rf communication problem about my project

Discussion in 'The Projects Forum' started by muratelbeyli, Mar 21, 2016.

  1. muratelbeyli

    Thread Starter New Member

    Mar 21, 2016
    4
    0
    Hey guys,

    I am Murat, I have just registered to your forum :) I have a serious problem about my project maybe you can help me? if you, i will be happy :) So here is my project.

    There are 1 circuit and 1 pc based serial communication, pc and circuit board are communicating with each other by using cheap 433 mhz rf modules
    Transmitter: Dra886tx
    Receiver: mx-rm-5v

    Both pc and circuit sides have these rx and tx modules together and each side they are working with same power supply.
    At the pc side power comes from USB port,
    At circuit board power comes from 7805 circuit,

    All connections true but i will sent to a diagram of my circuit later.
    Also my software correct too i tested all.

    My project is: pc sending a a string like "sent" via rf module to pic16f88 then pic reads this data and compare it with its own data array if this data same to pics' data array then pic reads an0,an1,an2 and sent these data to pc via rf module.But it doesnt work correctly in real life. I have done a lot of tests and i saw that rf rx and tx modules dont work with same power supply on pic side, on pc side they work together perfectly. I mean tx module work well with rx with same power supply but rx module cant work with tx with same power supply. If you unplug tx cable from pic, rx works perfect. Also if you attach a 100 uf to rx module and unplug the tx module antenna at 2-3 cm range pc and pic communicate i mean pic can receive data but cant sent without antenna. I tried to feed 2 modules with 2 7805 doesnt work. I also tried to attach diots to rf modules power lines nothing changed. A tried pull up and pull down resistors to data lines and it didnt work neither. So i need your help guys. Or i am going to be insane :| Thanks a lot i am waiting your replies.

    Best Regards,
     
  2. muratelbeyli

    Thread Starter New Member

    Mar 21, 2016
    4
    0
    Here is my diagram
    20160322_113541.jpg
     
  3. Sensacell

    Well-Known Member

    Jun 19, 2012
    1,128
    266
    It's hard to understand whats going on the way you phrase the explanation.

    In general, the TX module will require larger pulses of current, the power supplies may have trouble holding up the voltage during the transmit cycle.

    Try adding bypass capacitors connected to both TX and RX units power input, 200 uf in parallel with 0.1 uf ceramic capacitor- keep the leads VERY SHORT to the modules, not more than 10 mm long.

    See if this helps - also watch the power leads with an oscilloscope to see how noisy they might be.
     
  4. muratelbeyli

    Thread Starter New Member

    Mar 21, 2016
    4
    0
    I tried with 100 uf and 0.1 uf parallel nothing changed but i will try 200 uf too . Maybe attaching opto couplers to data lines will solve this problem what do you think?
     
  5. Sensacell

    Well-Known Member

    Jun 19, 2012
    1,128
    266
    Nope- that wont help.

    Post a photo of your setup?
     
  6. muratelbeyli

    Thread Starter New Member

    Mar 21, 2016
    4
    0
    Here is photo of my setup
    20160322_165913.jpg
    same as my diagram except two capacitors which are connected parallel to my rf rx module one of them 100 uf one of them 100 nf i tried 200 uf and 100 nf too but nothing changed.
     
  7. Sensacell

    Well-Known Member

    Jun 19, 2012
    1,128
    266
    I would ditch the breadboard as step #1 toward making it work.

    Solderless breadboards are not very good electrically, the high contact resistance of the connections and stray capacitance make them horrible for all but the simplest circuits- anything that uses high frequencies or draws pulses of high current will be unreliable on that board.
    Your circuit should be built on a piece of perf board with a heavy copper ground plane.
    A good solid ground is the foundation of any complex electrical system.

    Carefully check the specifications of the TX and RX modules to be sure you are supplying them with the correct voltages.
     
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