Problem with Ultrasonic Switch

Discussion in 'The Projects Forum' started by vivekde, Mar 18, 2011.

  1. vivekde

    Thread Starter New Member

    Oct 1, 2010
    could anyone plz see whether the circuits given below are correct or not..
    i m trying to light a led from the output port(6) of ca3140 without initially using the relay when i press the switch s1 in the input port..

    the link for the circuit is..

    the images are also attached
    but the problem there seems to be no output from input...
    also can anyone plz tell me 103 aec in capacitor is equal to 0.01 microfarad..?
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  2. Audioguru

    New Member

    Dec 20, 2007
    Your 103 capacitor is 0.01uF but it can be anything since it is just a filter. The 680 something capacitor value is very important since it sets the frequency. Maybe it is 680pF.

    The output of the opamp goes low when the receiver receives a signal.
  3. vivekde

    Thread Starter New Member

    Oct 1, 2010
    thanx for the answer.....
    the circuit claims to work at 40 khz..but the formula for frequency is
    f=1.44/(c1*((VR1+R1)+2R2)) ..putting the values we get..C1=680 micro farad,R1=4.7k Vr1=10k,R2=18k...then the value less than 1 hz .i think the circuit is wrong ...plz comment..
  4. Adjuster

    Well-Known Member

    Dec 26, 2010
    680 microfarad is obviously far too big. Audioguru suggested 680pF = 680 picofarad = 680*10^{-12} Farad.

    Using this value in your formula I get 41.8kHz.
  5. vivekde

    Thread Starter New Member

    Oct 1, 2010
    Thanks for the reply..i will use 680pF ..
    Another thing,can anyone tell me if 680aec equal to 680 pF or 680microfarad.
    As far i know 680 aec is 680 Microfarad and 681 aec is 680 pF..but the shopkeeper selling me the capacitor is insisting that 680aec is 680 pF..
    Am i wrong?
  6. Wendy


    Mar 24, 2008
    I think the aec is a distraction, it means nothing. The key is the number 681, which translates to 68X10^1, or 680 pF. This is a convention for very small capacitors. Microfarads almost always show the µ as part of the part value. If no prefex is included, pico is assumed.

    104 would be 10X10^4, or 100000pf. This is equivalent to 0.1µF. 105 would be 10X10^5, or 1,000,000pf, or 1.0µF. I have seen all of these parts.
  7. vivekde

    Thread Starter New Member

    Oct 1, 2010
    thank u all for the help