The first block is built on the NE555, which acts as a free-wave generator. VR1 50k potentiometer and C1 capacitor and VR3 100k potentiometer and capacitor C2 are responsible for the “rotation” speed. The VR3 potentiometer at maximum resistance...Electronics Projects, NE555 Super Siren Circuit "555 timer circuits, analog circuits projects, " Date 2019/08/04
The first block is built on the NE555, which acts as a free-wave generator. VR1 50k potentiometer and C1 capacitor and VR3 100k potentiometer and capacitor C2 are responsible for the “rotation” speed. The VR3 potentiometer at maximum resistance increases the rotation speed.
The rotation speed is in the range of 20 … 75 Hz. This value is approximate and is due to the tolerance of the capacitors. The rotation speed is reduced when we turn the VR3 100k potentiometer so that its resistance decreases to zero, then we get a rotation speed in the range of 0.02 … 3 Hz.
NE555 Siren circuit schematic
The NE555 oscillator frequency of the NE555 is in the range 110 … 2150 Hz. With the addition of a C5 capacitor to the combined capacities C3 and C4, the frequency range is 30 … 300 Hz. The frequency range adjustment is powered by the VR5 potentiometer. In addition, the SW2 rocker switch is connected in series with this potentiometer, which can be used to disconnect the VR5 22k potentiometer and the C5 capacitor.
NE555 has added a SW4 dual-ring switch to which the external pins connected to the cross have been soldered with the diode, and two center pins are connected to the voltage control input (pin5) and the output of the NE555 (pin3).
Adding a LED in the feedback loop causes the voltage to be summed as soon as the diode conductor voltage threshold is exceeded. This combination causes a stepping of the modulation voltage range, which allows for the original, “crazy” sound of our “siren”. In addition, the switch SW5 switches on behind the R6 resistor, which selects the type of siren sound.