Visible electric current circuit

Discussion in 'The Projects Forum' started by sahilsapre, Feb 7, 2009.

  1. sahilsapre

    Thread Starter New Member

    Feb 7, 2009
    1
    0
    I'm planning to build a variant of this circuit as a mini project for my design class.
    http://amasci.com/viselect/schem1.gif

    I need help analyzing it. Firstly, I haven't quite understood the operation of the precision full wave rectifier in the circuit. When I simulate it on Multisim, I don't get a full wave rectified output across the diodes. Is it a full wave rectifier? This is the designer's explanation of the circuit
    http://amasci.com/viselect/vistxt.html

    Secondly, what is the function of the transistor 2N3904 in the circuit? Thirdly, it's output goes to a series of NAND gates, whose function I am unable to figure out.

    I will greatly appreciate any help you guys can provide me.
    Thanks.
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Take a look at the connections between the diodes in the feedback for the first half of the TLO72 and the inputs of the other half. The second half is a difference amp. It is what keeps the output at one polarity.

    You can't drive LED's right off logic - or don't if you want the IC to last. Then 2N3904 switch current through the LED's.
     
  3. flat5

    Active Member

    Nov 13, 2008
    403
    17
    I think the transistor he is asking about is the one connected to the pot.
    As I see it, it is part of the direction circuit.
    "The polarity signal is level-shifted and is used to control the fwd/rev direction of a shift register."
     
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