Nowadays, most children’s toys like cars and bicycles are equipped with sirens. This siren can easily be made with few electronic components at home. This is a simple project that enables us to make a loud toy ambulance siren using two 555 timer ICs that are wired together to act as an astable multivibrator.
A multivibrator is a positive feedback regenerative switching circuit with analog timing of switching behavior. The astable multivibrator has actually no stable state. It has two quasi-stable states which rapidly alter from one to another and again to the same state. So it mainly alters from high to low and from low to high irrespective of any input trigger input after a pre-settled time. This circuit is enabled to generate quite a loud ambulance siren using a 6-12 V battery.
Hardware Components
The following components are required to make Toy Ambulance Siren Circuit
| S.no | Component | Value | Qty |
|---|---|---|---|
| 1. | Battery | 6V-12V | 1 |
| 2. | IC | NE555 timer | 2 |
| 3. | Speaker | 8Ω | 1 |
| 4. | Darlington transistor | TIP125 | 1 |
| 5. | Polar Capacitor | 4.7µF | 1 |
| 6. | Ceramic Capacitor | 10nF | 2 |
| 7. | Potentiometer | 200K | 1 |
| 8. | Resistors | 10K, 1K, 100K, 120Ω, 5.6Ω | 2,2,1,1,1 |
NE555 IC Pinout
For a detailed description of pinout, dimension features, and specifications download the datasheet of 555 Timer
TIP125 Pinout
For a detailed description of pinout, dimension features, and specifications download the datasheet of TIP125
Toy Ambulance Siren Circuit
Working Explanation
The circuit can be operated with 6 to 12V DC. The circuit is using two 555 timer ICs connected as astable multivibrators. The output pin3 of the IC1 is connected with the pin5 of IC2 to control the output frequency of the IC2. The output sound can be adjusted through a 200K variable resistor. The audio output is then amplified by Darlington transistor TIP125. 8 ohms loudspeaker can be used between 1 to 5-watt ratings.
Application and Uses:
This siren can be used in children’s toys like cars, bicycles, and trucks.
