Help for clap switch

Discussion in 'General Electronics Chat' started by Dzoro, Feb 13, 2019.

  1. Dzoro

    Thread Starter Member

    Feb 1, 2019
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    4
    36we7.gif this is the circuit that i built but the michropmhone sensitivity is too small do anyone know how to increase the sensituvity beacose i need to clap too close to the microphone so it can work and i want to be able to work at least 3m away if its possible.
    I thinked that if i use another transistor in series can help but that didn't change even so sligthly.
     
  2. AlbertHall

    AAC Fanatic!

    Jun 4, 2014
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    Is it a condenser mic or an electret? I suspect electret.
    Connect the mic to an amplifier and the output of the amplifier to Q1.
    Search your favourite engine for electret mic amplifier. There will be lots.
     
  3. Dzoro

    Thread Starter Member

    Feb 1, 2019
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    Yes i use electret mic but can you send some good amplifiers beacose you know better
     
  4. AlbertHall

    AAC Fanatic!

    Jun 4, 2014
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    I am no expert at designing audio amplifiers. I would just be looking at stuff on WWW and guessing which would work best.
    You might also search for clap switch designs and compare them with the circuit above.
     
  5. Dzoro

    Thread Starter Member

    Feb 1, 2019
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    I searched for clap circuit designs and this one is the best so far
     
  6. Audioguru

    Expert

    Dec 20, 2007
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    I looked at many clap circuits in Google and many of them will not work or work poorly like yours.

    1) The electret mic does not get enough current and voltage. Lookup its spec's. Current= 0.5mA. Voltage= typically a few but 2V minimum. Then the resistor at the mic should be (9V - 4V)/0.5mA= 10k, but not feeding current to the transistor.
    2) The transistor is biased like I was taught to never bias like that. Since a transistor has a wide range of DC hFE and has no negative feedback then many will be cutoff and many others will be saturated. The transistor needs an emitter resistor for DC negative feedback and its base should be biased with two resistors as a voltage divider. It will have lots of AC gain when its emitter resistor is biased with a capacitor. The DC base voltage should be separated from the DC mic voltage with a coupling capacitor.
    3) The pin 2 of the 555 needs a pullup resistor of about 22k and a coupling capacitor from the collector of the transistor.
    4) ALL electronic circuits should have a supply bypass capacitor on the circuit board, parallel with the battery.

    You show an old fashioned obsolete TTL 74S74 IC that will be killed since its maximum supply is only 7V. The battery will also be killed because the obsolete IC draws a high current all the time. use a CD4013 Cmos flip flop IC instead. You should also use a Cmos 555 IC instead of the high current old ordinary 555.
     
  7. AnalogKid

    AAC Fanatic!

    Aug 1, 2013
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    The transistor is acting as a comparator or peak detector with a threshold value of 0.6 V. The problem with the circuit is that this is too high for the electret element biased the way it is. Reducing R4 will increase the DC output voltage from the mic. The closer that no-signal output is to 0.5 V, the more sensitive the circuit will be.

    AND - the more sensitive the circuit will be to false actuation. It is a trade-off. This circuit has no filtering to differentiate between a clap and a big thump from something hitting the floor, so increasing the sensitivity might have issues.

    ak
     
  8. MrChips

    Moderator

    Oct 2, 2009
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    For starters, put a DC blocking capacitor between the output of the mic and the base of Q1.
    Add about 0.6V bias to the base of Q1.

    [​IMG]
     
  9. Audioguru

    Expert

    Dec 20, 2007
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    An electret mic has a "Sensitivity Reduction" spec for the reduction in its output level when its supply voltage is 1.5V instead of the recommended 2V to 10V. Most of them use a DC current of 0.5mA.

    With the 47k resistor shown and a 9V battery the 0.5mA in it results in a calculated ZERO voltage at the mic.
    But of course some mics use a little less than 0.5mA and the current drops more as the voltage across the mic is reduced.
    But the base-emitter 0.65V of the transistor limits the mic voltage to only 0.65V which is much too low.

    Sensitivity problem? When my dog goes Bark, Bark then this circuit will think about somebody clapping and count the barks. Yeah, also ,things that are dropped.
    No filtering? If I say Boooo then the circuit will go on and off hundreds or thousands of times. Nope, the 555 prevents multiple triggers.

    It is a horrible circuit.
     
    Last edited: Feb 13, 2019
  10. AlbertHall

    AAC Fanatic!

    Jun 4, 2014
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    Velleman make a clap switch kit. The user manual, including the circuit, can be downloaded here. The circuit is below. You can see that a lot more effort has been put into amplifying and filtering the mic signal.
    upload_2019-2-14_10-25-51.png
     
  11. Dzoro

    Thread Starter Member

    Feb 1, 2019
    53
    4
    Thanks for all the replays
    I found this circuit on the internet i am a begginer so i don't know much how horible or good is this circuit and i don't care if it goes on from other sounds i just want to work from few meters away.
    I will build an circuit with op amp lm 386 to amplify the signal and then we will see if it works and i am gona try the circuit that alberthall has put
     
  12. Audioguru

    Expert

    Dec 20, 2007
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    An LM386 is not an opamp. Instead it is a little power amplifier with built-in biasing and negative feedback. Its input must be at 0VDC so it will need an input coupling capacitor from the electret mic. You should connect a logarithmic volume control between the coupling capacitor from the mic and ground, and the input of the LM386. I don't know if a clap is a high frequency or low frequency for a suitable filter. Some people clap with high frequency Slaps and other people like me clap with low frequency Pops. Then maybe you should not filter the sound to let a dog or cat (Slap or Pop) trigger it, or motorcycle or jet airplane.
     
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