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Looking for help with circuit revision

Discussion in 'Electronic Basics' started by [email protected], Aug 17, 2007.

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  1. Guest

    The following circuit was designed for me by John...

    --------------------------------------------------

    So, your final circuit comes out looking like this:


    +5>---+-------------+
    | |
    [68k] [LDR] +---[1M]--+
    | | | |
    | +----+---|+\ |
    | | | >--+---->OUT
    [100K]<--[10K]---|--------|-/ |
    | | LM324 [1.5k]
    | [3.9k] |A
    | | [HLMP4700]
    | | |
    GND>--+-------------+--------------+---->GND


    I've added a little hysteresis to keep the output from chattering as
    the + input goes through the trigger point, and also used a
    high-efficiency LED to allow more output current from the opamp into
    whatever OUT is feeding.

    -------------------------------------------

    I now need to invert the output - is this something I can do with the
    existing components, or will I have to add an addtional invertor to
    the output?

    Any help greatly appreciated.

    Dave
     
  2. DJ Delorie

    DJ Delorie Guest

    Can't you just swap the + and - inputs?
     
  3. John Fields

    John Fields Guest

    ---

    This may work:

    .. +5>---+-------------+
    .. | |
    .. [68k] [3k9] +---[1M]--+
    .. | | | |
    .. | +----+---|+\ |
    .. | | | >--+---->OUT
    .. [100K]<--[10K]---|--------|-/ |
    .. | | LM324 [1.5k]
    .. | [LDR] |A
    .. | | [HLMP4700]
    .. | | |
    ..GND>---+-------------+--------------+---->GND

    But just to be sure, what was the original application?
     
  4. John Fields

    John Fields Guest

     
  5. Rich Grise

    Rich Grise Guest

    How about if you just swap them before the hysteresis feedback?:

    +5>---+-------------+
    | |
    [68k] [LDR] +---[1M]--+
    | | | |
    [100K]<--[10K]---|----+---|+\ |
    | | | >--+---->OUT
    | +--------|-/ |
    | | LM324 [1.5k]
    | [3.9k] |A
    | | [HLMP4700]
    | | |
    GND>--+-------------+--------------+---->GND


    Or, you could have turned the 324 upside down, as long as the 1M
    goes with it.

    Or am I missing something?

    Thanks,
    Rich
     
  6. Guest

    Thanks for the responses!

    The original application was a musical instrument triggered by
    interrupting laser beams.
    I'll give these designs a try.

    I've also been given a couple of GP2D120 reflection sensors - I know
    that the output of these is in the range of 0.4-2.45v. Can I adapt the
    above components to work with these instead?

    Thanks in advance - I wish I knew how to do this stuff myself.
     
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