In the deep end of the pool for me....

Discussion in 'General Electronics Chat' started by HBN, Mar 28, 2014.

  1. HBN

    Thread Starter New Member

    Mar 26, 2014
    I decided to improve on a motion detection circuit, but I am having difficulty understanding the circuit operation. Is there a place to post the schematic and seek advice?:confused:
  2. atferrari

    AAC Fanatic!

    Jan 6, 2004
    You are in that place. Your own thread.
  3. SgtWookie


    Jul 17, 2007
    You can attach an image of your schematic to your initial post.
    Click the "Edit post" button.
    Then click the "Go Advanced" button under the text box
    Then click "Manage Attachments"
    It's best if you upload .png format files from your own computer. The upload dialog is pretty much self explanatory. Note that you are limited as to the size of the files, but the size limit is usually plenty - particularly for images like schematics.
    .jpg format files are "lossy", and not very useful for schematics because they will be very difficult to read. .png format files are compact and not "lossy".
    PackratKing likes this.
  4. HBN

    Thread Starter New Member

    Mar 26, 2014
    Any help explaining what this circuit is doing would be welcomed.
    Note - The actual resistor/cap values might not be accurate.

    If the Rf antenna signal is triggering the comparator on the bottom left, why have all the op amp in the circuit?

    The upper right comparator output goes to a PIC processor.

    Last edited by a moderator: Mar 30, 2014
  5. dougy83


    May 11, 2011
    Where is that schematic from? It doesn't look like it's from a real device, and doesn't appear to capable to doing anything useful.

    The bottom comparator (gate 2) forms a squarewave oscillator. opamp 4 is a simple buffer of the filtered (by r37/c13) squarewave. Opamp 2 further filters and amplifies this by a factor of two.

    The components around comparator 1 appear to be missing connections to ground. Opamps 2 & 3 don't have any effect on anything. The RF input is ignored. VR1 is likely not drawn correctly.
  6. HBN

    Thread Starter New Member

    Mar 26, 2014
    It's from a real motion sensor I would like to modify by adding bluetooth least that's my ambition.

    This is only a partial circuit. I will retrace the circuit, correct anything which is incorrect and repost.

    Tracing circuits is tedious ........
  7. HBN

    Thread Starter New Member

    Mar 26, 2014
    Thank you for feedback.

    I have attached an updated schematic diagram correcting a few things. I am confident the circuit is correct except for actual resistance and capacitance values. Determining the actual values is taking more time than originally expected.

    The strip antenna (on a 8 inch by 3/4 inch) PCBA has only the receiving antenna which connects into L1 on the circuit. If it helps I could post a picture of the antenna. Could the RF from the antenna be used somehow to adjust the potentiometer levels during setup and using Op amps 2 & 3 ???? It seems odd that they wouldn't come into play somehow but then again I am way in over my head here........ I assume the antenna RF is a very small signal.
  8. HBN

    Thread Starter New Member

    Mar 26, 2014
    I updated it to add additional details around Comparator #1.

    There is actually a three position switch with position #2 and #3 shuntting the resistors.