Data Transmission project

Discussion in 'Embedded Systems and Microcontrollers' started by Eplanet, Apr 21, 2008.

  1. Eplanet

    Thread Starter Active Member

    Oct 25, 2007
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    hi friends
    do you know how can i use with this data transmitter and receiver with PIC micro because this device have 4bit for data how can i use it ?
    HM-EP is transmitter
    HM-D is receiver
    thanks
     
  2. Papabravo

    Expert

    Feb 24, 2006
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    Sure it seems straight forward to me.
    On the trnasmitter, anytime a bit goes low 6 address bits and 4 data bits get transmitted.

    On the receiver, anytime an FSK message is received with the correct 6 address bits the 4 data bits match the 4 data bits in the incomming message.

    Seems like you can transmit fifteen different messages. I don't think it is possible to get a message of all 1's.
     
  3. Eplanet

    Thread Starter Active Member

    Oct 25, 2007
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    thanks for replay
    please tell me more about how can i send 4bit data with PIC.
    for example i want to send a "A" character over RS232(transmitter) and i should define "B0 var byte" in PIC is it true?
    byte = 8bit but i must send 4 bits in transmitter(D0...D30) how can i do it ?and how about receiver?

    final question: you said me "On the trnasmitter, anytime a bit goes low" what does it mean?
    thanks in advance
     
  4. Papabravo

    Expert

    Feb 24, 2006
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    You have several things all mixed together. Sending data with the RF transmitter and receiver is not at all related to sending data over an RS-232 connection.

    On your transmitter module when all four of the data bits are high or logic '1' the transmitter is idle. When one or more of the four data bits makes a transition from the logic '1' or high state to the logic '0' state then the transmitter will send a total of 10 bits. Six of the bits will be the address bits selected by the switches and the remaining four wil be the data bits including the one which went low to trigger the process. That is why I said you cannot transmit the data "1111" because there is no way to trigger that transmission. Only nybbles (4-bit quantities) with at least one zero in them can be transmitted.

    You cannot transmit arbitrary ASCII characters with this system even if you break the characters into 4-bit nybbles because you cannot transmit "1111" which you would need to do for the character 'O' which in hexadecimal is 0x4F. You could do it with one or two or three bits at a time with the forth bit being an active low strobe.
     
  5. Eplanet

    Thread Starter Active Member

    Oct 25, 2007
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    thanks do you have any book or pdf for more about these modules i want to know more about this issue.
    and are you programming PIC microcontroller in Picbasic pro???
     
  6. Papabravo

    Expert

    Feb 24, 2006
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    I have no books or ".pdf" files on these modules except for the links you posted. Everything I've told you is based on those documents.

    I've never used PICBASIC PRO. I have programmed them in assembly language and HI-TECH C. That's it -- sorry.
     
  7. Eplanet

    Thread Starter Active Member

    Oct 25, 2007
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    as you told me i did low one of the pins of data (D0) that never all pins goes high(idle state).
    and send 3bits of a variable to transmitter with this address: A0=high and A3= high and send data from pc (Typing) but i didn't see anything in receiver.
    should i do any working?
     
  8. Papabravo

    Expert

    Feb 24, 2006
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    If you connect any kind of square wave generator to D0, then a receiver with the same address as the trnasmitter should cause it's D0 to beat up and down with some delay.

    BTW you need to make sure that each one of the address bits has a defined level. Make them either one or zero. DO NOT leave them floating or unconnected. It will increase power consumption and lead to unreliable operation.
     
  9. Eplanet

    Thread Starter Active Member

    Oct 25, 2007
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    in this receiver all data bits (D0-D3) are always high (5V) do you know why ?
     
  10. ex-navy

    New Member

    Apr 22, 2008
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    This transmitter and receiver are really only designed to be for security or garage door opening, not to send RS232.

    Take a look at any Zigbee wireless modules if you want to send RS232 data
     
  11. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    If you are referring to the data sheet, the data pins set to the high state when powered on. That is simply going to a known state. They will follow the transmitted data when it is received.

    As has been noted above, the devices are not intended for communication. The data they send are codes selected by the address switch selection. If the received code matches the selection at the receiver, then the control function (open the garage door) is enabled.
     
  12. Eplanet

    Thread Starter Active Member

    Oct 25, 2007
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    you said true but i wont use rs232 for sending data .
    this data whit rs232 comes to PIC with DB9 socket and send again from pic to transmitter module and this output it can be not only rs232.
     
  13. Eplanet

    Thread Starter Active Member

    Oct 25, 2007
    42
    0
    ok as you told me this module not great for sending data and i using this module due to have address code for securing data.
    but i have other module that haven't any hardware code you can see in this attachment.
    i know this module is great for this project but i don't know how can i set code for this because when sending data from transmitter, receiver getting unwanted noises very fast and show in my lcd maybe because this modules work in 915MH near mobile frequency.
    i really need to set any code maybe software that these modules getting only data from themselves not other data.i could send and receive my data from this modules very great but only getting unwanted data.
    can you help me?
     
  14. Papabravo

    Expert

    Feb 24, 2006
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    I have no clue, but the address bits must be connected identically with the trnasmitter or the receiver will ignore all incoming trnasmissions.
     
  15. Eplanet

    Thread Starter Active Member

    Oct 25, 2007
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    do you have any method for encoding this (HM-T and R) that don't getting any noise???
     
  16. beenthere

    Retired Moderator

    Apr 20, 2004
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    282
    There is some problem in understanding here - the Tx & Rx devices do not work as and are not meant to send variable data. The sole function of the transmitter is to send a code that results from the address switch selection. The sole purpose of the receiver is to compare the received code with the set address bits it has. If they match, it generates a logic signal that can start opening/closing a garage door.

    If one wished to use one of these transmitters to send data, he would have to make up a table of codes, one for each address switch combination. These would be selected by using the data to address the chip in place of the switches. The receiver is very limited. It might be necessary to scan through the addresses to generate a code match, which could then be decoded back to ASCII or whatever. The problem is that there will be some minimum time to scan all address switch combinations and wait for a match indication. That time is then the minimum time for each transmission. And there's no way to handshake the process.

    Smoke signals might be faster.

    Reading the brag on the switch to FSK indicates that the maker is quite happy about signal-to-noise improvements. The transmission only has to cover 50 meters or so. Reading an earlier post or the data sheet will let you discover why the data bits come on in the high state.
     
  17. Eplanet

    Thread Starter Active Member

    Oct 25, 2007
    42
    0
    hi
    thanks but i have already stated that (HM-T and R) this is different and haven't any address code. and have rs232 input for data transmission look at the data sheet.
    due to haven't any address code i need to make software code maybe use "CRC based framing"
    i am looking for software programming.
     
  18. Papabravo

    Expert

    Feb 24, 2006
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    Either you are not reading the datasheets or you do not understand what you are reading. Both devices have six, count 'em six, address bits. In order for proper operation all six bits MUST be hardwired to GND or VCC to select one of 64 unique addresses. THEY MUST BE THE SAME FOR BOTH the transmitter and the receiver or there will be no data coming out of the receiver. What do you not understand about this process?
     
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