siren circuit simulates police, fire or other emergency sirens

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.

The 0.1 uF determines the pitch of the siren: A 0.047uF will give a higher pitch siren and a 0.001 uF will give an ultrasonic (at least for me, anyway) siren from 15 to 30 kHz which might have an interesting effect on the neighborhood dogs! The 33k resistor from the collector of the PNP to the base of the NPN widens the pulse to the speaker giving greater volume.

The flasher circuit drives a PNP transistor which powers the speaker. This transistor may be a small-signal transistor like the 2N4403 in most applications since it will not dissipate much power thanks to the rapid on-and-off switching. The 100 ohm and 100uF capacitor in series with the speaker limit the current to about 60 mA and they may be replaced with a short circuit for a louder siren as long as the transistor can take the increased current. The prototype drew about 120 mA when shorted which is fine for the 2N4403.

Transistor substitutions should be fine – try just about any small-signal transistors but avoid high frequency types so that you do not end up with unwanted RF oscillations.

Mini Metronome by 555 Timer/Oscillator IC

This mini metronome gives a linear scaled output and 40 to 208 beats per minute.

Circuit Operation: 1- Q1 and Q2 transistors provide linear frequency variation of IC1 depending on the changes of P1 value. 2- Q3 amplifies the click sound output and gives louder beats. 3- To provide a higher output , a 12V micro battery is used. It also makes the circuitry more compact. 4- Rotate the P1 potentiometer fully towards R2, then set R1 to obtain 40 beats per minute by the help of another metronome.

P1	100K Linear Pot
R1	10K 1/2 Watt Trimmer Cermet
R2	10K 1/4 Watt Resistor
R3	330K 1/4 Watt Resistor
R4	50K 1/2 Watt Trimmer Cermet
R5	100K 1/4 Watt Resistor
R6,R7	1K 1/4 Watt Resistor
C1	1uF 63V Polyester Capacitor
C2	10nF 63V Polyester Capacitor
IC1	NE555 Timer/Oscillator IC
Q1,Q2	BC560C PNP Transistor
Q3	ZTX753 PNP Transistor
SW1	SPST Switch
SPK	8 Ohm 40mm Loudspeaker
B1	12V Battery (MN21, GP23A or VR22 type)

Components List:

Read More Source: http://www.redcircuits.com/Page8.htm

Mini Trombone Sound generator by LM3909

This be Mini Trombone Sound generator circuit. By using integrated circuit the number LM3909 of NS. In using loudspeaker 25 Ohm sizes work by use voltage from AA 1.5V battery. In sound occurrence that resemble with trombone.
It have the work depends on the principle uses voltage, which the generator by the occurrence Resonance of sound coil of a loudspeaker is feeding gets back to the way adds to give with integrated that circuit was set up in large-sized box,which there is the capacity about 64 inch cubic which one side of a box has can to move in and out resemble a cylinder a position of a piston.
The work of switch press will cause the tone of voice that resemble very integrated loudspeaker circuit and battery touch set up on a piston , which there are 5 size inch pipes. For be born air push reaches and go out while a piston moves by don’t affect to build the frequency Resonance. The frequency of origin frequency circuit will begin to equal to the frequency Resonance of a box.

source: elecfree.com