Confusing Clap Switch System

Discussion in 'Homework Help' started by NewbSolutions, Nov 7, 2011.

  1. NewbSolutions

    NewbSolutions Thread Starter New Member

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    http://talkingelectronics.com/projects/200TrCcts/101-200TrCcts.html#37

    I'm trying to understand how the circuit works(the clap switch circuit over there) for our basic electronics class but I'm having problems analyzing the circuit, since I don't really understand this part...

    "...when a sound is detected, the negative excursion of the waveform takes the positive end of the 10u towards the 0v rail. The negative end of the 10u will actually go below 0v and this will pull the two 1N4148 diodes so the anode ends will have near to zero volts on them..."

    ...and pretty much everything in the explanation fails to penetrate my thick skull... I have a basic understanding of KVL, BJT analysis and diodes... though not capacitors outside AC circuits... since from my understanding they are supposed to block DC currents? though initially it allows them to pass through until the capacitor gets fully charged, in which case it will then block any more current from passing through... I also think those LEDs have a 10mA minimum current aside from the voltage drop(since they aren't ideal, I think... or is this only for zener diodes?).

    also not really sure what happens to the electret mic when a sound is heard, though I think the capacitance of the capacitor hooked to the gate of the JFET changes? or something....

    and shouldn't the two LEDs turn on at the start? since they'll pass through 270R, LED, capacitor(while it charges), the base->emitter portion of the BJT(since it functions as a diode if I remember correctly) until the capacitor dies, but then the BJT will then allow current from the collector to emitter for both of them?

    I'm not really sure how this works....
    and for the assignment, we're supposed to justify the values of the resistors, capacitors... so I'm not sure, though I think the 47k and 33k resistors are there to soak up most of the voltage so the current will be too small to power the LEDs? though not sure what difference the different capacitances of the capacitors do... or what the 270R resistors are for...

    sorry, but I'm still very new at this so any help will be appreciated... I'm so sorry for being so inadequate ><
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