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RF COMMUNICATION WITH MICROCONTROLLER

Discussion in '8051/8951' started by ORGENES, Feb 3, 2016.

  1. ORGENES

    ORGENES New Member

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    Hi everyone..

    I work on project of message sending between two micro controllers using RF modules. Help me the choice of micro controllers and RF modules. Also help me on circuit diagram.
     
  2. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    hi,
    We need more information about your project.
    eg: distance between the two MCU's, data transmission rates etc.
    E
     
  3. ORGENES

    ORGENES New Member

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    Thanks, Distance between micro controllers is 100metre which is the distance between transmitter and receiver since one micro
    controller is at transmitter and another at the receiver.
    Also data transmission rate to be 10kbps.
    operating frequency of RF modules 433MHz.
     
  4. dave

    Dave New Member

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  5. MikeMl

    MikeMl Well-Known Member Most Helpful Member

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    100meter range will work only with very good antennas, both at the transmitter and at the receiver (not just a pcb trace or a whip: must be full dipole, likely outside). Will work only if not blocked by another transmission on the same (shared) frequency. 315Mhz works better in urban areas; 433Mhz is hopeless in urban areas because of all the other uses of that frequency.

    If you dont believe this, listen near 433.92MHz +- 50kHz on a scanner.
     
    Last edited: Feb 3, 2016
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  6. ORGENES

    ORGENES New Member

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    Thanks Mike,

    Can i helped on block diagram and circuit?.
     
  7. jpanhalt

    jpanhalt Well-Known Member Most Helpful Member

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    I just used a pair of ZigBee modules. Just sent the output in whatever format you want (1-wire + ground), receive with the mated module and you are done.

    John
     
  8. atferrari

    atferrari Well-Known Member

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    Steep learning curve, John?

    Realistic distance in line of sight?

    What modules did you use?
     
  9. gophert

    gophert Active Member

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    If it is the cheap 433MHz modules from eBay, you will be lucky to get 8kHz across the room.
     
  10. jpanhalt

    jpanhalt Well-Known Member Most Helpful Member

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    atferrari M
    Model S1 XBee from a few years ago. Adafruit adapter board. Range about 6 m line of sight with no antenna on either end. The plug functions as the on/off switch and for battery charging. Batteries are Li-ion. The cover has a matching hole, which can be plugged to make it reasonably watertight when in use. The sensor is under the XBee and is my Memsic accelerometer.
    upload_2016-2-4_1-9-24.png
    John
     
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  11. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    hi,
    I use the NRF24L01 2.4GHz transceiver, the best I can get using the PCB etched antenna is 8 metres thru a brick wall.
    Both the Base and Remote TXR pcbs are mounted vertically.
    The project is a Base station with 4 Remotes/Pipes.

    I do have some 2.4GHz dipole antenna's which I plan to try, when the weather improves.:)
    Web posted documentation suggests that with a dipole I should get 100 metres.

    E
     
  12. granddad

    granddad Active Member

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    Last edited: Feb 4, 2016
  13. jpanhalt

    jpanhalt Well-Known Member Most Helpful Member

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  14. NorthGuy

    NorthGuy Well-Known Member

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    I don't think you can achieve 10kpbs with 433MHz at 100m.

    I have built few RF gadgets to control things on my land. They exchange short messages at 1kpbs. The distances are perhaps a little bit longer than 100m in some cases, and there's some trees in between. I used ready-made Linx modules, so there's not much of a cirucuit except two wires from MCU to the module and a wire from the module to antenna. Antenna helps a lot. I use simple ones, but you can use directional Yogi antenna. It is supposed to work better, but I haven't tried it myself. You also must use some narrow-bandwidth encoding, such as Manchester, otherwise it's totally hopeless.
     
  15. ORGENES

    ORGENES New Member

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    Thanks i get u good Mr North Guy, and i think you have more knowledge, so what you advice me? and can you give a circuit diagram?
    I got you that, i should use 1kbps and a distance of about longer 100m, so how the circuit will be to achieve this?
     
  16. MikeMl

    MikeMl Well-Known Member Most Helpful Member

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    It is all about using a complex protocol that validates messages (checksums, parity, sending it multiple times), because any given transmission can be stepped on by another (unrelated) 433MHz transmission. You have no control of who else is using the frequency.

    The simplistic super-regenerative receiver in those inexpensive modules you bought locks on to the strongest signal it hears within +- about 2Mhz. If you are trying to get long range, your own transmission will be very weak, and subject to getting clobbered by other signals. Antenna gain, and directional antennas will help some, but that also receives the interfering signals better:(
     
  17. NorthGuy

    NorthGuy Well-Known Member

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