Clapper circuit question. Please help

Discussion in 'The Projects Forum' started by ddaann11, May 6, 2011.

  1. ddaann11

    Thread Starter New Member

    May 6, 2011
    Hello all,
    This year for my introductory Electronics course, we have been assigned to create a clapper circuit that turns on an LED after one clap, and Turns the LED off after two claps. So far I have the microphone wired to an omp-amp, and then after that I am really very lost on where to go next.
    I was talking to the instructor and he hinted that a monostable 555 timer would be a nice place to go after the op-amp. I understand the capabilities of a monostable 555 timer, just not why it would be useful after the op-amp(which is inverted by the way). Then there is the logic which has to recognize the number of claps (within a certain time limit, aka where the 555 timer comes in again), which I am confused on.
    The last main question I have so far, is how a logic gate of any type could recognize two successive signals coming from the wire and turn it into memory.
    Any Help would be appreciated, thank you.
  2. JDT

    Well-Known Member

    Feb 12, 2009
    I have attached a simplified sketch of what your circuit has to do.

    First, amplify to audio signal from the microphone.
    Next, rectify the amplified signal to produce a DC level proportional to the loudness of the sound.
    Then, detect a threshold DC level and use this to switch your LED.

    So that it switches on at the first clap and off at the second, I suggest using a "toggle" flip-flop as shown.

    The threshold detector has to produce a sharp edge as the slowly changing DC level goes above and below the threshold. I have drawn a "schmitt trigger" for this. This can be part of a logic IC such as the 4093 or you could make it with an op-amp or comparator and feedback resistors. For the flip-flop you could use an IC like the 4013.
  3. ddaann11

    Thread Starter New Member

    May 6, 2011
    Thanks JDT, I appreciate the post,
    I showed this to my TA which started us on a discussion that helped to answer a lot more questions that I had in the back of my head. I appreciate it
  4. Audioguru


    Dec 20, 2007
    You must think about the difference between two hand claps and two barks from a dog.
    Maybe a highpass filter will pass the hand claps and reject the low frequencies of a dog barking. Maybe your circuit will work when you shout, "OPEN NOW" or "BEEP BOOP" but will not work when you shout a single word.