A Wailing Siren Circuit using IC 555 is simple to make sound like real siren, going up and down in pitch, also the sound come from 555 IC making pulses at certain speed (frequency).
Circuit Working:
Parts List:
| Components | Values | Quantity |
|---|---|---|
| Resistors | 390Ω, 1k, 220k, 100k, 33k, 22k 1/4 watt | 1 each |
| Capacitors | Ceramic 10nF | 2 |
| Electrolytic 100μF 25V | 1 | |
| Semiconductors | IC 555 | 1 |
| Transistor BC547 | 1 | |
| Transistor BC557 | 1 | |
| Speaker 8Ω | 1 | |
| Push Button | 1 |
555 IC work in astable mode with no need of outside trigger as it oscillate by itself, also resistors R3, R4 and capacitor C3 control how fast it oscillate and then this R3, R4 and C3 set pitch of siren sound which changes them to change pitch.
Pin 3 of 555 give high low voltage because C1 charges and discharge through R5.
Furthermore, transistor T1 BC547 acts as a switch and responds to the output from pin 3 and when pin 3 goes high, T1 turns ON, allowing current to flow through the speaker and consequently, the speaker produces sound.
Then transistor T2 BC557 control power to 555 IC and when push button pressed then T2 turns ON and power goes to 555 and then the circuit starts.
Release button then T2 is OFF and and then the circuit stops.
Finally, pin 3 continuously changes its voltage and switches transistor T1 ON and OFF as capacitor C1 charges and discharges.
Consequently, the speaker produces a pulsing sound, furthermore, the charging and discharging rates of C1 determine the pitch, while R3, R4 and C3 set these rates.
Formulas:
Main goal of the circuit is the siren sound by using 555 IC in astable mode and by changing frequency output.
Use this formula for frequency (f):
f = 1.44 / (R1 + 2R2) × C
where,
- R1 and R2 are resistors.
- C is timing capacitor.
Duty cycle D tell how long high and low sound stay:
D = R2 / (R1 + 2R2)
We can change R1, R2 and C to adjust siren sound and how it behaves.
How to Build:
To build a Wailing Siren Circuit using IC 555 follow the below mentioned process for connections:
- First, put all parts like in circuit diagram and then connect pin 1 of 555 IC to ground.
- After that, connect pin 2 and pin 6 together.
- Now connect capacitor C1 from pin 2 & 6 to ground.
- Also, pin 3 goes to base of transistor T1 through resistor R2.
- Pin 4 goes to 6V positive supply and also pin 8 goes to 6V positive.
- Next, pin 5 connect to ground with capacitor C2 and pin 6 connect to pin 3 with resistor R5.
- Now T1 collector connect to 8 ohm speaker and resistor R1 and then to 6V, T1 base connect to pin 3 with resistor R2 and then T1 emitter goes to ground.
- Also, T2 collector connect to pin 4 and 8 of IC, T2 base connect to resistor R4 and positive of capacitor C3 also C3 negative goes to ground and then T2 emitter goes to 6V.
- Lastly, between R4 and C3 connect resistor R6 and push button in series to ground.
Safety Tips:
- Use right value parts, do not short power supply and be very careful.
Conclusion:
To conclude, Making this Wailing Siren Circuit using IC 555 is fun and good for learning, where we can change sound pitch by changing parts.
Finally, tis small project show how 555 IC make sound effects.