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Data amplification?

Discussion in 'General Electronics Discussion' started by rinchan6, Aug 28, 2013.

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  1. rinchan6

    rinchan6

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    Aug 27, 2013
    I searched for RF circuits and found out that others use a transistor between Encoder to Module or Module to Decoder and I don't know what is the difference if you just transmit digital data.

    For example, this circuit:
    random.png
    the Encoder data output is at pin 4 and being fed to a transistor before TX

    1.) what does it amplify?
    2.) is it just for switching?
    3.) what if i feed the Encoder Data Output to the Module directly?

    Any additional information will help me a lot for I am self studying :D
     
    Last edited: Aug 28, 2013
  2. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Nov 28, 2011
    The transistor is used for inversion, i.e. it inverts the data.

    When the signal on pin 4 of the RF803E connector is high, the transistor's collector (which drives the input of the TX434) is low. When RF803E pin 4 is low, the collector is high. So the signal is inverted.

    The likely reason for this inversion stage is that the standard definition for the data signal on the RF803E connector is the opposite from the signal that's required by the TX434.

    The transistor COULD also be used as a buffer, to increase the current available to the TX434.

    If you can provide more information about the device that connects to the RF803E connector, and the TX434, we can give you a better answer. Can you provide links to data sheets for these devices?
     
  3. rinchan6

    rinchan6

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    1
    Aug 27, 2013
  4. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
    1,270
    Nov 28, 2011
    Thanks for the links to the data sheets.

    Unfortunately, both of them are poorly written and lack detail.

    The RF803E generates a 7-byte packet at 9600 bps using Manchester coding, twice per second. It's not clear whether it transmits continuously, or just when one or more of the input switches is closed.

    The wireless transmitter accepts a serial data stream and transmits it using amplitude shift keying (ASK). This means that the RF carrier wave has two possible amplitudes, depending on the state of the data input.

    Unfortunately the data sheet does not state the modulation depth, nor does it tell you which state (high or low) on the data input corresponds to the low and high carrier amplitudes.

    The only reason for the inversion state, that I can think of, is to reduce power consumption of the transmitter, by ensuring that the low carrier amplitude on the transmitter corresponds to the idle state of the data from the encoder IC.

    For example, if the RF803E's data output is normally high (in between transmitted data packets), and the transmitter transmits a low carrier amplitude when its data input is low, then an inversion stage is needed between them, so that the transmitter will spend most of its time transmitting a low amplitude carrier. (A low amplitude carrier will require less current from the battery.)

    So that is my guess at why the inversion stage is present. I don't have enough information to be sure.
     
  5. rinchan6

    rinchan6

    42
    1
    Aug 27, 2013
    thanks for your time Krisbluenz, i will try to find another good encoders with full detail datasheets

    chan
     
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