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The sample and hold circuit , as its name implies, samples an input signal and holds on its last sampled value until the input is sampled again. Figure shows the Circuit Diagram of a SAMPLE AND HOLD Circuit using 741 OP AMP with an E-MOSFET. In this circuit the E-MOSFET works as a switch that is controlled by the sample-and-hold control voltage Vs, and the capacitor C serves as a storage element. Read More.....

MOSQUITO REPELLENT ELECTRONIC CIRCUIT DIAGRAM It uses IC CD4047 to control the buzzer timing utilizing resistor and capacitor. When the voltage passing through the transistor, the buzzer would sound.     Variable resistor R1 : 10K ohm     Polar capacitor C2 : 4.7 nF/16V     Capacitor C3 : 22uF     IC1 : CD4047     NPN transistor Q1-Q2 BC547     PNP transistor Q3-Q4 BC557     Buzzer K1 : Tweeter 8 ohm     Power supply : 12V