microcontroller interface RF transmitter... HElp!!

Discussion in 'Embedded Systems and Microcontrollers' started by marine, Apr 15, 2010.

  1. marine

    Thread Starter New Member

    Apr 6, 2010
    4
    0
    im doing a wireless ECG, and im having troubles in the wireless part,

    im using PIC16f877a, to act as ADC, and then send the data to the RF transmitter.
    the analog signal from the ecg amplifier is working just fine, but when its connected to pic, i get nothing from output..:confused:

    i attached the schematic and the codes for the pic,
    plz advice me if it's correct or not..?

    i also attached the receiver schematic, the block diagarm:
    RF-RX704>> MAX232>> RS232..to PC to display signal..

    thank aloot..:)
     
    Last edited: Apr 16, 2010
  2. rjenkins

    AAC Fanatic!

    Nov 6, 2005
    1,015
    69
    That transmitter appears to be a 'dumb' radio module (ie. no internal CPU), so you need to correctly format the data to be transmitted.

    The modules I've used in the past need a 15mS run-in with dummy data for the DC levels in the transmitter and receiver to settle before valid data can be guaranteed.

    They then need continuous data for the duration of the transmission, as the signal path is internally capacitor coupled - if you leave a steady mark or space on, they lose track of what level it's supposed to be and the first few mS of data following will be corrupt.

    There are also usually limits on the data mark/space duty cycle, like it's supposed to stay in the 20% - 80% range (so no continuous $00 or $FF bytes) so the receive data slicer can work properly.

    That is a very high power module at 1W - typical modules are 10mW.
    Regulations, even for the low power stuff we use require the transmitter to be shut down when data is not actually being sent.

    Also remember that the radio channels are shared; other people will pick up what you transmit and you may pick up what other people transmit - anything from garage door openers to outdoor thermometer and wireless security systems etc.

    The data you send should be packetized, with a run-in sequence, a set of samples, then error checking or CRC data so the receiver can verify it's a valid data frame using 'your' error check code, ignoring random noise and other equipment that it may hear.

    The transmitter should be enabled, the data frame sent, then the transmitter shut down until another buffer full of data is ready.

    If you just want to send data ad-hoc, you need 'intelligent' radio modules that do all the transmit control and error checking for you.

    Where abouts in the world are you? It's a lot easier to suggest info & possible suppliers etc. if you fill in your user info so people can see what country you are in.
     
  3. marine

    Thread Starter New Member

    Apr 6, 2010
    4
    0
    im actually using KST-TX433Mhz transmitter, RF modules from Cytron products. their architecture very simple but i guess tedious to use...
    no much info provided in the datasheet ***attached..

    wat i know is that im using the PIC for AD conversion and to feed the data to the transmitter in serial format via USART.. because the transmitter has only one input pin..
    but it seems not to working at all for me.. i tried alot and triple check the connections and codes with my senior frens, but none hv figured it out..

    wat i think, if i get over this problem, the whole transmission and receiving stuff should be fine..

    i didnt get to the receiver part , coz im stuck in transmitting the data.. precisely, getting a correct output from the pic !!

    plz if u do hv any suggestion, hook me up with ..
    i edited my profile...:D
    thanks alot Robert Jenkins

    Tariq Maz..
     
  4. marine

    Thread Starter New Member

    Apr 6, 2010
    4
    0
    anyone got a clue, suggestion?

    i think the problem is simple, but i can't see it,
    anyone does ??!!!

    thanks
     
  5. rjenkins

    AAC Fanatic!

    Nov 6, 2005
    1,015
    69
    You don't seem to have posted any program code for people to coment on?
     
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