Police Siren

Intro:

This police siren requires a transition between two tones or frequencies. This transition between two tones is made possible by using two 555 timers, the second one being in astable mode. We connect the second 555 timer's output to the control pin of the first 555 timer. This gives us two different frequencies from the second 555 timer. Using the supplies below and following the schematic, you will create a low-frequency oscillator to produce a square wave of voltage at the output pin. The output voltage drops and rises instantly due to the capacitor charging and discharging behind the input voltage. The trigger and threshold waveforms are responsible for this. When the voltage dips below 1/3Vcc, the negative pulse on the trigger sets the internal flip-flop, causing the output to switch from low to high. When the voltage surpasses 3/2Vcc, the threshold pin sets the internal flip-flop, making it to switch from high to low state. As a result, the voltage is kept bouncing between 1/3Vcc and 2/3Vcc by these two. The trigger and threshold waveforms oscillate as they do in the circuit as a result of this. The voltage control pin of the second 555 timer is controlled by the output from the low-frequency oscillator. The frequency of the second oscillator rises and falls in response to voltage changes in the voltage control.

• Two 555 timers
• Jumper wires
• Breadboard
• 68k Resistor
• 1k Resistor
• Two 10k Resistors
• Two 100n Capacitors
• Two 10u Capacitors
• Speaker (internal resistance of 8 ohms)
• 15V Power Supply