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Simple Powerful Siren Circuit Schematic Diagram (BC557)

2015-01-08 10:34  
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This circuit operates with 12V DC, with purpose to obtain more power than the siren circuit already and to avoid the use of ICs. With a simple and usual use parts, this device are easy to made and very portable. The complementary transistor pair (Q2, Q3) is wired as a high efficiency oscillator, directly driving the loudspeaker.

This article describes the Simple Powerful Siren Circuit Schematic Diagram (BC557). The content is very simple, very helpful. Components in this article can help you understand better understanding of this article. For example, in this article, you can go to find and buy these components:BC557.


R1,R3——————————————1K 1/4W resistors

R2,R5——————————————10K 1/4W resistors

R4———————————————-220R 1/4W resistor

R6———————————————-220K 1/4W resistor

R7———————————————-22K 1/4W resistor

R8———————————————-100K 1/4W resistor

C1,C2——————————————22uF 25V electrolytic capacitors

C3———————————————10nF 63V polyester or ceramic capacitor

C4———————————————47uF 25V electrolytic capacitor

Q1,Q2—————————————-BC557 45V 100mA PNP transistors

Q3———————————————BC337 45V 800mA NPN transistor

SW1——————————————-SPST toggle or slide main switch

P1———————————————-SPST pushbutton switch

SPKR——————————————8ohm loudspeaker

B1———————————————12V battery

Q2 ensure a full charge of C2 when power is turned on. Pressing on P1, C2 gradually discharge trough R8. The circuit starts oscillating at low frequency that increase slowly until a high steady tone is reached and keep indefinitely. When P1 released, the output tone frequency decrease slowly as C2 is charged to the battery positive voltage through R6 and the base emitter junction of Q2. When C2 is fully charged, the circuit stop oscillating, reaching the stand-by status.

A good sized loud speaker will ensure a better and powerful output tone, maximum current at full output is about 200mA



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