Factory Siren

This schema produces a sound similar to a factory siren.It makes use of a 555 timer Ic used as an astable multivibrator of a center frequency of about 300Hz.The frequency is controlled by the pin 5 of the IC









When the supply is switched ON, the capacitor charges slowly and this alters the voltage at pin 5 of the IC hence the frequenct gradually increases.
After the capacitor is fully charged, the frequency no longer increases. Now when the push button siren control switch is held depressed, the capacitor discharges and the siren frequency also decreases.
The presets VR1 and VR2 should be adjusted for optimum performance.

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Single IC Dual tones Siren Circuits Wiring diagram

Double-tone Police sound Circuits Diagram

This schema is intended for children fun, and can be installed on bicycles, battery powered cars and motorcycles, but also on models and various games and toys. With SW1 positioned as shown in the schema diagram, the typical dual-tone sound of Police or Fire-brigade cars is generated, by the oscillation of IC1A and IC1B gates. With SW1 set to the other position, the old siren sound increasing in frequency and then slowly decreasing is reproduced, by pushing on P1 that starts oscillation in IC1C and IC1D. 

The loudspeaker, driven by Q1, should be of reasonable dimensions and well encased, in order to obtain a more realistic and louder output. Tone and period of the sound oscillations can be varied by changing the values of C1, C2, C5, C6 and/or associated resistors. No power switch is required: leave SW1 in the low position (old-type siren) and the schema consumption will be negligible.

Single -IC Dual-tones Siren Circuits Diagram

Parts:

R1,R3___470K1/4W Resistors

R2______680K1/4W Resistor

R4_______82K1/4W Resistor

R5______330K1/4W Resistor

R6_______10K1/4W Resistor

R7_______33K1/4W Resistor

R8________3M31/4W Resistor

C1,C5_____10µF25V Electrolytic Capacitors

C2,C6_____10nF63V Polyester Capacitors

C3_______100nF63V Polyester Capacitor

C4_______100µF25V Electrolytic Capacitor

D1-D3___1N414875V 150mA Diodes

IC1_____4093Quad 2 input Schmitt NAND Gate IC

Q1______BC33745V 800mA NPN Transistor

P1______SPST Pushbutton

SW1_____DPDT Switch

SPKR____8 Ohm Loudspeaker

B1______6V Battery (4 AA 1.5V Cells in series)

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Build a Toy Siren Wiring diagram Schematic

This simple Toy Siren schema for hobbyist and student who game liker, this is a very simple Toy Siren schema,  This Toy Siren schema can be built small enough to frt inside a toy. The Toy Siren schema consists of a relaxation oscillator utilizing one uni-junction transistor (2N2646, MU10, TIS43). R2 and C2 determine the frequency of the tone. 

 Simple Toy Siren Circuit Diagram

Pushing the button, SW1 charges up the capacitor and the potential at the junction of R2 and C2 rises, causing an upswing in the frequency of oscillation. On releasing the push-button the charge on C2 will drop slowly with a proportional reduction in the frequency of oscillation. Manual operation of the button at intervals of approximately 2 seconds will produce a siren sound.

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