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Practical electronic alarm circuit diagram

2016-02-18 11:44
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This article is practical electronic alarm circuit diagram. The principle is simple and very practical. Want more thoroughly grasp the principle, you should understand and be familiar with the major components of the circuit, such as: BC108B . When the first opened 10 u capacitor discharge and two transistors are off. When the button switch according to 10 u capacitor will charge by 22 k resistor. The voltage is applied to basic BC108B this will open slowly. When will release switch capacitor discharge by 100 k and 47 k base resistance and the transistor will slowly turn off. Change the voltage frequency siren. This oscillator action more difficult work. As BC108B transistor switch in the collector voltage drop, 2 n3702 transistor to open. This will happen soon (less than 1 us). 22 n capacitor will charge also very quickly. The capacitor connection between 2 n3702 collector and bottom BC108B, quickly reached almost all of the power supply voltage. Charging current of capacitor is much reduced and the collector emitter voltage of 2 n3072 thus increase; The collector could fall. The change in voltage by the bottom of the 22 n capacitance BC108B slightly out of saturation. As this occurs it will rise and collector voltage of the switch off 2 more n3072 transistor. This process continues until the two transistors are off. 22 n capacitor will discharge through the 100 k and 22 k resistor, close button switch, 9 v battery, speaker and 56 ohmic resistance. Time it will take about 5 to 6 msec emissions. As long as 22 n capacitor discharge, BC108B transistor will switch and repeating this cycle. In the voltage difference in the collector BC108B (due to the charging 10 u capacitor) lead to the tone of the siren changes. With 10 u capacitor charging, the tone of the siren will rise, because it emits, it will fall. A 64 ohm speakers can be used instead of 8 ohm and 56 resistors, the value of the components can be changed to produce different sound effects.