Clap switch kit is composed of a number of resistors, capacitors and transistor amplifier circuit. Circuit is simple, welding easy, inexpensive, and can be widely used in voice-activated switch.

• 1.The electrical characteristics
  Operating voltage: 4.5 ~ 5V
  PCB size: 28 * 49mm
  
  2.The circuit theory
  This circuit mainly by the audio amplifier circuit and a flip-flop circuit.
  Q1 and Q2 form a secondary audio amplifier, an audio signal received from MK1 C1 is coupled to the base of Q1, the amplification is fed directly from the collector to the base of Q2, the collector of Q2 to obtain a negative square wave with to trigger the bistable circuit. R1, C1 limit the frequency response of the circuit for the high sensitivity range of about 3kHz. When the power is turned on, the state of the bistable circuit is off Q4, Q3 saturated, D3 does not shine. When MK1 to a control signal output after the two-stage amplification of a negative square wave, after the differential processing by the negative spike D1 added to the base of Q3, the circuit rapidly inverted, D3 is illuminated. When MK1 again received control signal, the circuit took place flip, D3 extinguished. The board reserved for external control devices connected to terminals J1, can be a voice for other devices connected via J1 relay. (When connected to both ends of the relay coil relay to be anti and a diode)
  
  This circuit uses a DC 5V power supply, turn off the machine when the LED current of 3 mA, the LED lights up the whole current of 6mA.
  
  3.Circuit schematics
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• 4.Parts lists
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• 5. Welding to note
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Arrow pointing at the two pads, need to use wire links
As shown below:

Why change it:
This is when the effect of the wiring board, the figure where the red circle there was a small mistake, take the line did not come on the pads, a little bit worse, make friends, their answer it by the above method.

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