This Panic Alarm helps old aged people and those who are in bed rest to catch the attention of others in case of an emergency . It generates a loud Ambulance Siren when its Button is pressed. It can also be used as a Personal alarm during travelling. If there is any threat or emergency situation, it can help you to invite the attention of others. It is too compact ,handy , battery operated and can be kept in the bag or pocket. Its cost is just Rs.80 including battery.
Designed and developed by D.Mohankumar
You need the following components
1. 3K3 Resistor – 1
2. 220K Resistor – 1
3. 100 uF 25V Electrolytic capacitor -1
4. 470uF 25 V Electrolytic capacitor -1
5. 0.1 uF ( 104) Disc capacitor -1
6. 3V 400 mW Zener diode – 1
7. IC UM3561 – 1
8. IC LM 386 – 1
9. Push switch – 1
10. 8 Ohms Speaker -1
11. 9V Battery -1
12. 9V Battery Snap -1
The circuit uses the Siren generator IC UM 3561. It is a ROM (Read Only Memory) chip that generates 4 different types of Sirens like Police siren, Ambulance siren, Fire engine siren and Gun sound based on its pin connections. Here in this circuit, the IC generates Ambulance siren because its pin 6 is connected to ground. UM 3561 is a low volt IC and it works very well in 3 volts and its maximum voltage rate is 5V.
Since 9 V battery is used, a 3V Zener diode is used to regulate the input voltage of the IC to 3V. Resistor R1 is the current limiter for the Zener. Resistor R2 (220K) determines the oscillations of the IC and hence its tone. Do not change its value and use only 220K. Since the output from the IC is feeble, either a Transistor or IC based amplifier is needed to get loud sound.
Here IC LM386 is used as a simple low power amplifier. Output tone from UM3561 passes to the Non inverting input (Pin 3) of Amplifier LM386. It then produces the loud siren. You can also add an LED with 1K series resistor to get visual indication also.
Enclose the circuit inside a small case. Press the Push switch to generate the siren.