Today security is big problem everywhere; many time thief try to open bag or suitcase in bus, train or station, therefore, we cannot always keep our eye on our luggage.
So this small Luggage Safety Alarm Circuit using IC LM358 is a solution which help to protect our bag, as it uses piezo sensor and LM358 to sense vibration.
When someone touches or tries to open the bag, the buzzer sounds loudly, therefore, this circuit is simple, low-cost, and easy to hide inside a suitcase.
Circuit Working:
Parts List:
| Components | Values | Quantity |
|---|---|---|
| Resistors | 12k,1M 1/4 watt | 1 each |
| Potentiometer 20k | 1 | |
| Semiconductors | IC LM358 | 1 |
| Sensor Piezoelectric Disc | 1 | |
| 5V Buzzer | 1 |
This circuit main part is piezo sensor and this sensor make small voltage when it feel vibration or shock.
Output voltage is weak so we use LM358 IC and this LM358 work here as comparator; then comparator check sensor voltage with reference voltage.
Furthermore, if sensor voltage is more than reference then output go high and buzzer gets ON; then resistor R2 give bias to sensor.
After that, use the VR1 potentiometer to set the sensitivity and if we set VR1 to a higher level, even small vibrations can trigger the alarm; also R1 acts as a pull-down resistor and keeps the comparator stable.
When the bag remains still, the sensor detects no vibration, the output stays low and the buzzer remains OFF.
When someone touches or lifts the suitcase, the sensor detects the vibration, the comparator output goes high and the buzzer sounds an alarm.
Formula:
Comparator output is HIGH when V+ is more than V-, here, V+ is piezo sensor voltage plus bias from R2 and V- is reference voltage from VR1.
So condition is:
Vpz + Vbias > Vref.
- Vpz is sensor voltage from 0.1V to 2V based on vibration.
- Vbias is small voltage across resistor R2 of 12k.
- Vref voltage set by VR1 from 0V to 5V.
By moving VR1 we can set threshold, for example: if Vref is 1V then sensor plus bias must be more than 1V, then comparator output goes high and buzzer sound.
How to Build:
To build a Luggage Safety Alarm Circuit using IC LM358 follow the below steps for connections:
- First, collect all parts as in circuit diagram.
- Next, pin 1 of LM358 connect to buzzer through resistor R1.
- Then pin 2 of LM358 (inverting -) connect to one side of piezo sensor and pin 3 of LM358 (non inverting +) connect to other side of piezo sensor.
- Also, connect pin 4 of the LM358 to ground 0V and connect pin 8 to the +5V supply (Vcc).
Note:
- The piezo sensor detects vibrations easily when mounted on the suitcase body.
- VR1 fixed on small PCB so user can adjust
- Buzzer connected to output and placed hidden in bag.
- Whole circuit powered by 5V small battery pack.
Conclusion:
Overall, this is easy and useful mini project, also this Luggage Safety Alarm Circuit using IC LM358 protect from thief.
Circuit is small, low cost and uses less power and we can adjust VR1 sensitivity of sensor; also we can add relay for big siren or GSM module for SMS alert.
Finally, best part is circuit need few components and fit on small PCB for portable use.