Security Alarm | Electronic Project Circuits

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Emergency Siren circuit Simulates Police

This siren circuit simulates police, fire or other emergency sirens that produce an up and down wail.
The heart of the circuit is the two transistor flasher with frequency modulation applied to the base of the first transistor. When the pushbutton is depressed, the frequency of oscillation climbs to a peak and when the button is released, the frequency descends due to the rising and falling voltage on the 22 uF capacitor. The rate of change is determined by the capacitor value and the 100k resistor from the pushbutton. The oscillation eventually stops if the button is not depressed and the current consumption drops to a tiny level so no power switch is needed.

Read more original source: http://www.techlib.com/electronics/noisemakers.html

Be the first to comment - What do you think? Posted by admin - June 22, 2008 at 12:42 pm

Categories: Audio diagram, home alarm systems Tags: Audio diagram, electronic siren, security alarm

Powerful Siren by BC337

This circuit was requested by several correspondents. Its purpose was to obtain more power than the siren circuit already available on this website since many years (One-IC two-tones Siren) and to avoid the use of ICs.
A complementary transistor pair (Q2 & Q3) is wired as a high efficiency oscillator, directly driving the loudspeaker.
Q1 ensures a full charge of C2 when power is applied to the circuit. Pressing on P1, C2 gradually discharges through R8: the circuit starts oscillating at a low frequency that increases slowly until a high steady tone is reached and kept indefinitely. When P1 is released, the output tone frequency decreases 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 stops oscillating, reaching a stand-by status.

Parts:
[...]
C1,C2___________22ÂµF 25V Electrolytic Capacitors
C3______________10nF 63V Polyester or Ceramic Capacitor
C4______________47ÂµF 25V Electrolytic Capacitor
Q1,Q2_________BC557 45V 100mA PNP Transistors
Q3____________BC337 45V 800mA NPN Transistor
SW1___________SPST Toggle or Slide Main Switch (See Notes)
P1____________SPST Pushbutton Operating Switch
SPKR__________8 Ohm Loudspeaker
B1____________12V Battery

Please read more at the original source: http://www.redcircuits.com//Page84.htm
Thank you.

Be the first to comment - What do you think? Posted by admin - January 2, 2008 at 9:54 am

Categories: Alarm systems, Automotive, Basic electronics Tags: electronic car horn, electronic siren, security alarm

One-IC two-tones Siren with IC 4093

Double-tone Police sound Single-tone old ambulance sound

This circuit 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 circuit 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 circuit consumption will be negligible.

Parts:
R1,R3___470K 1/4W Resistors
R2______680K 1/4W Resistor
R4_______82K 1/4W Resistor
R5______330K 1/4W Resistor
R6_______10K 1/4W Resistor
R7_______33K 1/4W Resistor
R8________3M3 1/4W Resistor
C1,C5_____10µF 25V Electrolytic Capacitors
C2,C6_____10nF 63V Polyester Capacitors
C3_______100nF 63V Polyester Capacitor
C4_______100µF 25V Electrolytic Capacitor
D1-D3___1N4148 75V 150mA Diodes
IC1_____4093 Quad 2 input Schmitt NAND Gate IC
Q1______BC337 45V 800mA NPN Transistor
P1______SPST Pushbutton
SW1_____DPDT Switch
SPKR____8 Ohm Loudspeaker
B1______6V Battery (4 AA 1.5V Cells in series)