Help needed creating an amplification circuit.

Discussion in 'General Electronics Chat' started by halfacandan, Apr 10, 2006.

  1. halfacandan

    Thread Starter New Member

    Apr 10, 2006
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    In short, I'm trying to increase the voltage going to one of the pins in a Euro SCART AV lead from around 2.3V to 7V-9V. The pin only carries an on/off voltage so my idea is to use an external supply (a 9V battery) to boost the signal. However, I don't want the battery to always be on and don't want to turn it on/off manually.

    I am completely new to electronics (appart from some long-forgotten Physics from high school) so my efforts sofar have been inept at best. Here's the problem in more detail:

    I plan to make an adaptor which sits between the (male) SCART plug and my TV's (female) socket. The adaptor itself would have a female socket, to accept the source plug and a male plug to attach to the TV.

    SCART Socket.
    Pin 8 = "channel selector" (2.3V when the source is "on", relative to pin 17 - this needs to increase to ~7V)
    Pin 17 = (Video)Ground

    All signals/pins would be wired to pass straight through except pin 8 (and pin 17? - I don't know). I read up a little last night and made a circuit with an NPN transistor (acting as a switch) this morning. I was trying to get the 2.3V to allow the 9V to flow through the collecter & emitter which I them connected to the appropriate pins connecting to the TV.

    It almost worked except that the current flowed through the collecter/emitter even when the 2.3V was not present i.e. when the source was turned off.

    Does anyone know of: the correct way of setting up the circuit; an easier way to achieve the same result (I know I can manually select the channel on my TV but where's the fun in that :D) or a pre-made device which boosts the voltage on pin 8 of a Euro-SCART?

    Any help is much appreciated.

    Thanks
    Dan
     
  2. halfacandan

    Thread Starter New Member

    Apr 10, 2006
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    I've just found something on the web about a step-up converter/boost converter. Would this be suitable?

    Dan
     
  3. windoze killa

    AAC Fanatic!

    Feb 23, 2006
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    First question is why do you need to do this?

    This site http://www.bnoack.com/data/cables/scart-pinout.html show pin 8 as being 9.5V to 12V for a high and 0V to 2V for a low. This would put your 7V in a neutral zone and may not do anything.

    Also the step up/boost convertor may work but can't really say as we have no idea what it is. An ignition coil on a car is technically a step up convertor. If you can supply a schematic or a link to it it would help.

    Overall your idea of a 9V battery should work. And if the cct is design properly then there will be no current drain from the battery when it is off.
     
  4. halfacandan

    Thread Starter New Member

    Apr 10, 2006
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    I think each TV varies slightly. The 2.3V volts doesn't do anything with my TV. When I had the battery linked up, it worked fine. 9.5V to 12V would be ideal.

    Sorry, I thought it was a standard electronic principal :D There seem to be lots of variations on it but this one seems simplest.

    Thanks for your help.
    Dan
     
  5. halfacandan

    Thread Starter New Member

    Apr 10, 2006
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    I just read that link that you gave me and describes what I am experiencing:

    High (9.5-12V) AVmode
    Low (0-2V) TVmode

    A low signal won't switch a TV into AV mode (which is what I want).

    Dan
     
  6. kubeek

    AAC Fanatic!

    Sep 20, 2005
    4,670
    804
    And what is your voltage when the signal is high?
    Just in case you didn´t understand, the VCR or whatever can send two signals - High meaning AV mode and Low meaning TV mode.
    To me it seems that it always sends low and that´s the real problem. You should find how to make it send the high signal, instead of trying to get high from low.

    Or you want to make it High->TV mode and Low->AV mode?
     
  7. halfacandan

    Thread Starter New Member

    Apr 10, 2006
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    I reread my last post an realised that it wasn't too clear. I realise that my TV sees ~2V as low and ~9+V as High. The source (a games console) outputs ~2V when on (high) and (as far as I know) it can't be made to output more than that. It is an american model which isn't made to use a EURO SCART plug hence the tiny 2V output to pin 8 instead of the necessary 9V.

    I think that my options are to directly raise the 2V to 9V or use a switch/external 9V source circuit. However, I don't know enough about electronics to tell which of these is easier/feasbile.

    Thanks
    Dan
     
  8. halfacandan

    Thread Starter New Member

    Apr 10, 2006
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    The site I linked to above says:

    There's not circuit diagram though so I'm stuck. I found the TL496's datasheet (here) but it only shows a circuit for use in an AC system. It seemed to suggest that the chip is made to be used with batteries os sources of 2-3V output, raising them to 9v.

    Am I on the right lines now?


    Thanks
    Dan
     
  9. halfacandan

    Thread Starter New Member

    Apr 10, 2006
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