Emergency Siren Simulator


Posted on Feb 5, 2014

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 det


Emergency Siren Simulator
Click here to download the full size of the above Circuit.

ermined 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. link




Leave Comment

characters left:

Related Circuits

  • New Circuits

    .

     


    Popular Circuits

    VUTRAX PCB CAD
    Capacitive-sensor-alarm
    Potentiometer-Position V/F Converter
    Linear Resistance Meter
    switch mode power supply design of current load sense circuit
    vu meter schematic
    The Xonar Essence STX
    SemiAutonomous Submersible robot for underwater research
    HD44780 Character LCD Displays Tutorial
    Robot Tutorials current sensor
    12v sensor light



    Top