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Build a Powerful 200mA Security Siren Circuit
Description
This circuit was requested by numerous individuals. Its objective was to achieve a greater output level than the existing siren circuit available on this website (One-IC two-tones Siren) and to minimize the incorporation of integrated circuits. A complementary transistor pair (Q2 & Q3) is configured as a high-efficiency oscillator, supplying direct power to the loudspeaker. Q1 facilitates a complete charge of C2 upon application of power to the circuit. Pressing on P1, C2 gradually discharges through R8; consequently, the circuit begins oscillating at a low frequency that increases progressively until a high, stable tone is reached and maintained indefinitely. When P1 is released, the output tone frequency decreases gradually as C2 is replenished by the battery positive voltage through R6 and the Base-Emitter junction of Q2. Upon C2 being fully charged, the circuit ceases oscillating, entering a standby condition.
Circuit Diagram:
Parts:
- P1 = SPST Pushbutton Operating Switch
- R1 = 1K
- R2 = 10K
- R3 = 1K
- R4 = 220R
- R5 = 10K
- R6 = 220K
- R7 = 22K
- R8 = 100K
- C1 = 22uF-25V
- C2 = 22uF-25V
- C3 = 10nF-63V
- C4 = 47uF-25V
- Q1 = BC557
- Q2 = BC557
- Q3 = BC337
- B1 = 12V Battery
- SW1 = SPST Toggle or Slide Main Switch
- SPKR = 8 Ohms Loudspeaker
Notes:
Using a larger loudspeaker will result in a superior and more powerful tone output. Due to zero stand-by current draw, SW1 can be omitted and B1 can be wired directly to the circuit. The circuit’s maximum current consumption at full output is approximately 200mA.
More about components
The use of integrated circuits, specifically the BC557 and BC337 transistors, offers several advantages in this design. These components are small, reliable, and provide efficient amplification and switching capabilities. The BC557 is a general-purpose NPN transistor commonly utilized in various electronic applications, while the BC337 is a PNP transistor offering complementary functionality. Their inclusion contributes to the circuit's overall performance and minimizes the need for discrete components, simplifying the design and potentially improving reliability. The transistors’ ability to amplify small signals enables the creation of an oscillator circuit with relatively low power consumption, ensuring an efficient and robust design. These particular ICs were selected for their availability, affordability, and appropriate characteristics for the circuit's specific requirements.