Low voltage adjustable signal amplifier?

Discussion in 'The Projects Forum' started by smp375, Mar 21, 2009.

  1. smp375

    Thread Starter Member

    Mar 21, 2009
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    I would like to build a circuit that can amplify by 0-50%, a variable low voltage (0.0-1.0VDC) signal, but I need to have an adjustable output. Where do I start?
     
  2. t_n_k

    AAC Fanatic!

    Mar 6, 2009
    5,448
    782
    Hi smp375,

    Not clear about your specification - but if you never need to amplify by more than 100% then you actually have an attenuator. At its simplest this could be done with a potentiometer between the source and output.

    Maybe you have a more detailed statement of your requirement.
     
  3. smp375

    Thread Starter Member

    Mar 21, 2009
    14
    0
    Well, my electronics experience is extremely limited, with only a basic understanding of most components and their functions, basic principles of electricity, soldering, and schematic reading.
    The best way I can describe my requirement is that I have a variable DC signal that can be anywhere between 0 and 1 volt. I would like to take control of that voltage by being able to step it up between 0 to .5 volts. So the input would be between 0 to 1 volt, output would be .5 to 1.5 volts at max gain, but still needs to be able to vary between 0 to 1 volt at minimum gain. Is that better? Then, if it's not too difficult, (this isn't as important) I would like the maximum output not to be able to exceed 1 volt, even at maximum gain. I understand that last part may be more difficult to achieve.
     
  4. t_n_k

    AAC Fanatic!

    Mar 6, 2009
    5,448
    782
    Still unclear about from where the input is derived - is it a DC supply for instance...?

    and what is the output being fed to ...?

    In principle you need a level shifter.

    You could try something like the attached circuit ...

    View attachment Level shiter.pdf

    VR1 (200Ω pot) is adjusted to set the 0.5V output offset. The LM134 is temperature sensitive so the offset will drift over a large temperature range - can be allowed for

    See the LM134 data sheet http://www.national.com/mpf/LM/LM134.html

    The LM134 will operate over a reasonably wide input voltage range so the 9V is just a suggestion - if you want to use a battery say - which could run down in voltage a few volts without compromising operation.

    Note: The circuit may not integrate well with your input/output requirements.

    I'm sure there are plenty of other options - I was looking at something reasonably easy to make and test.

    :)
     
  5. smp375

    Thread Starter Member

    Mar 21, 2009
    14
    0
    I'm looking into building a hydrogen boost system for my car; so to answer your question, the signal would be coming from an oxygen sensor, and the output would be going to the car's computer. The purpose of the circuit would be to maintain the proper air:fuel ratio in the engine while a hydrogen boost system is operating, but have the ability to return to the baseline if the hydroxy gas was turned off.

    The problem is that the Brown's gas increases combustion efficiency, thus creating a false lean condition, which is then mistakenly adjusted for by the ECU, in turn creating a true rich condition; this nullifies the fuel economy gains delivered by the hydrogen, and increases pollution. On the HHO forum it is suggested that in order to maintain the stoichiometric air:fuel ratio you can modify either the oxygen sensor signal, or the MAP sensor signal. I was interested in figuring out what would need to be done to modify the oxygen sensor signal to the computer. Frankly, I don't like the idea of doing that, I feel like there has to be a better way of allowing the ECU to function properly with the addition of hydrogen. My car is highly modified, I can't take any risks with the air:fuel ratio, so I can't install a hydrogen boost system unless I can overcome this problem. I'm talking with a professional Saab tuner about how to get around this without altering the oxygen sensor or MAP signals.
     
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