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Transistor switching

Discussion in 'General Electronics Discussion' started by Dolarmak, Mar 16, 2015.

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  1. Dolarmak

    Dolarmak

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    0
    Mar 16, 2015
    Hey guys,
    I'm working on a project where I am sending digital signals from a keyboard into a FM transmitter and then retrieving the signal and inputting it into a PIC.

    The issue I have is the output of the decoder I have doesn't output to a proper voltage for my FM transmitter. A friend suggested I use a transistor switch to boost the voltage of the signal so it matches what I need but I'm not sure what I'm supposed to do.

    I have a 5 V supply and need to boost a .5 V digital signal to a 1.375 V. Then I also need to boost the 1.375 V my receiver outputs to 5 V. I have a bunch of 2n3904 transistors.

    I looked online and I found a few diagrams of how it should work, but when I implement them it doesn't. I tried this one and used a voltage divider on the Emitter to get 1.375 V but when i test it on the scope I get a small square wave at .3 V. Oh and I removed the capacitor cause it distorted my signal.
    [​IMG]


    If any one has any suggestions on building it, or know a different method, I would appreciate it.
     
  2. Arouse1973

    Arouse1973 Adam

    5,165
    1,087
    Dec 18, 2013
    Is this a PC keyboard? Can you link to the data sheet for both the transmitter and the receiver modules you are using. The data from the keyboard will also be inverted, is this an issue?
    Adam
     
  3. Dolarmak

    Dolarmak

    2
    0
    Mar 16, 2015
    Yes it's a PC USB Keyboard, the Decoder converts it into ASCII pulses which my PIC 887 can translate. When hooked directly to the PIC it works fine. As for the FM transmitter and Receiver I made them from scratch with a LM565 and the schematic i had from a book on electronics i found. It works on 100KHz, could that be the issue? Its not meant for long range, just from 1 room to another. Transmitter.jpg Receiver.jpg
     
  4. Arouse1973

    Arouse1973 Adam

    5,165
    1,087
    Dec 18, 2013
    I don't quite understand why the keyboard is only outputting such a small voltage. How are you measuring this? The information I have found regarding the VCO output says it's a square wave, you are not going to be able to transmit very far if at all with this without some kind of resonant circuit on the output. Which book did you get this from? Does it say it will do what you wanted it to do or have you modified it in any way?
    Adam
     
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