Simple Shock Sensor Alarm Circuit

The Simple Shock Sensor Alarm Circuit is a simple but effective design that can detect vibrations or shocks and then trigger a loud alarm using a piezo buzzer.

This easy shock sensitive alarm circuit that can be used in lots of places from homes to automobiles.

This circuit is also useful for different purposes like security systems, preventing theft and detecting movement.

The main parts of this circuit include a vibration sensor the IC LM358 operational amplifier and a piezoelectric buzzer.

In this article we will look into how the shock alarm circuit works, examine its key components and talk about the calculations needed to adjust its sensitivity.

Circuit Working:

Parts List:

In this post the vibration sensor is the main part that detects movement and is connected to the inverting terminal of the operational amplifier IC1.

The circuit is powered with 3V battery supply.

The non inverting terminal gets its voltage from a reference point created by two resistors R1 and R2.

The job of the operational amplifier is to compare the signal from the vibration sensor with this reference voltage.

When the sensor detects a vibration or shock it sends a signal that makes the output go high.

When the circuit is turned on with the S1 switch, IC1 starts checking the signal from the vibration sensor.

If there are no vibrations the voltage at the inverting terminal stays higher than at the non inverting terminal keeping IC1s output low.

But if a vibration or shock happens the sensor sends a quick signal that drops the voltage at the inverting terminal below the reference voltage at the non inverting terminal.

This change makes IC1s output go high which then activates the buzzer through diode D1 creating a sound alarm.

After the vibration stops the sensors output levels out causing the operational amplifiers output to go back to low which turns off the buzzer.

Formulas with Calculations:

Below are the formulas with calculations for designing Simple Shock Sensor Alarm Circuit:

Setting the Reference Voltage (Vref):

Vref = (R2 / (R1 + R2)) * Vcc

where,

• Vcc is the supply voltage 3V in this case
• R1 is the 15k
• R2 is the 22k adjustable potentiometer.

By adjusting R2 the reference voltage can be fine tuned to control the sensitivity of the circuit.

Operational Amplifier Comparator Behavior:

Vout = Vcc, if V+ > V-
Vout = 0, if V+ ≤ V-

where,

• V+ is the non inverting terminal voltage reference voltage
• V- is the inverting terminal voltage sensor signal

Calculation Example :

For a supply voltage Vcc = 3V:

If R2 is set to half its maximum value 11k:

Vref = (R2 / (R1 + R2)) * Vcc
Vref = (11k / (15k + 11k)) * 3V
Vref = 1.27V

This reference voltage will determine the threshold at which the buzzer activates.

How to Build:

To build a Simple Shock Sensor Alarm Circuit follow the below mentioned steps:

• Gather all the component as mentioned in the above circuit diagram
• Connect pin 1 of IC1 LM358 to anode of diode D1 and cathode of D1 to on end of buzzer and the other end of buzzer to GND.
• Connect pin 1 of IC1 LM358 one end of resistor R3 and the other end of R3 to pin 3 of IC1 LM358
• Connect pin 2 of IC1 LM358 to negative terminal of piezo and connect the positive terminal of piezo to pin 3 of IC1 LM358
• Connect resistor R1 one end to positive supply and the other end of R1 to pin 3 of IC1 LM358.
• Connect a one leg of pot VR1 to pin 3 of IC1 LM358 and second leg of VR1 to GND.
• Connect one leg of S1 SPST switch from pin 8 of IC1 LM358 and the other leg of S1 switch to positive (+) of 3V battery and connect the negative (-) of 3V battery to GND.
• Connect pin 4 of IC1 LM358 to GND.

Conclusion:

The Simple Shock Sensor Alarm Circuit is a cool and simple project that can sense vibrations or shocks and sound an alarm.

You can change the sensitivity by tweaking the potentiometer and choosing the right parts making it suitable for different uses.

This circuit shows how an operational amplifier IC LM358 can work as a comparator and how easy it is to mix basic components to build a useful electronic system.

It is especially great for DIY electronics fans who want to explore security and alarm systems.

References:

Datasheet IC LM358