I need some help with a basic clap switch

Discussion in 'The Projects Forum' started by StToonz, Dec 3, 2012.

  1. StToonz

    Thread Starter New Member

    Nov 30, 2012
    14
    0
    Hey guys,

    I am building this schematic (First Picture) it is a re-draw of THIS schematic (second) as of first build it doesnt work. I only have 2n3904 NPN's or 2n3906 PNP's so replace those in your head. The specific mic that i have for this is an electret button mic. I figured it is going to take me a while so i might as well start this thread now since i will be researching this until it works for Wednesday.

    Your help is greatly appreciated.

    thanks
     
  2. wayneh

    Expert

    Sep 9, 2010
    12,093
    3,033
    One thing you can do is divide and conquer. Check if a negative going pulse on pin 2 triggers the 555 to turn on the light. Depending on how you made your build, break the connection between Q2 and C1 and tap the C1 side of the break alternately from V+ and then to ground. If that works, you'll know that side of the circuit is fine.

    And all the transistors in that circuit are NPNs. Are you saying you've actually used a PNP somewhere?

    An electret is not equal to a condenser mic.
     
  3. StToonz

    Thread Starter New Member

    Nov 30, 2012
    14
    0
    no i didnt use any PNP's sorry.

    a dilema that i thought i had solved is i have a 9v battery and this is a 6v circuit, now im still an early student, i tried building a simple voltage divider with 3 1k resistors to give the circuit 6 volts but i still can seem to read 6v for power input of the circuit. my first resistor drops about 8 volts, the middle resistor drops 0 ( and its not a bad resistor ive switched it many times) and the final resistor drops 1 volt. what the hell is going on man? please tell me you have something?

    and ya an electret mic is all i have. will i have to go get an actual condenser mic?
     
  4. Bernard

    AAC Fanatic!

    Aug 7, 2008
    4,170
    395
    Electret mic's generally have three leads, + -& out; should work. R2 looks low, "would guess 47k as more normal. With cap coupling to pin 2, need a pullup resistor, 10k to 100k, or leave out cap. 'Think biasing first stage would help. Use 9V, or as mic or relay requires.
     
  5. wayneh

    Expert

    Sep 9, 2010
    12,093
    3,033
    That won't work, as you've shown. Things besides the resistors, namely your circuit, are drawing currents that are large compared to the current flowing through your divider, which is 9V/3000Ω = 3mA.

    Your divider would work fine if all you were "powering" was the (high impedance, low current) input of your volt meter.

    You should be fine with 9V as long as you limit current on any component (LED, relay, etc.) to stay within its specs.
     
  6. KrisBlueNZ

    Member

    Oct 17, 2012
    111
    14
    The obvious problem is the amplifier stages are DC-coupled and therefore the biasing is going to be very critical. With the values given, it's not going to work at all. I would replace them all with an op-amp stage, and capacitively couple the input from the electret microphone. (These need either a separate supply rail, or a bias voltage, because they have a FET inside them.)

    After that problem is fixed, it will still make a pretty poor clap detector, because it will respond to ANY sound. A clap has certain useful characteristics that make it distinctive - it contains a lot of high frequencies, and it consists of a short loud burst followed by relative quiet (depending on how reflective the room is). Therefore a good clap detector will contain a high-pass filter and some circuitry to detect a short burst of sound followed by no sound. Typically this would be better done by a microcontroller but it might be possible to get good performance with a discrete circuit.

    I suggest you look around for a better circuit. That one is pretty poorly designed.
     
  7. sheldons

    Active Member

    Oct 26, 2011
    616
    101
    also,regarding pin two the 555 trigger ,theres no pull up resistor to supply ....it might not reliably trigger the 555 every time with the circuit as shown....
     
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