Simple Suitcase-Lift Alarm

By Praddep G. He is B.Sc. (Physics) and a regular contributor to international magazines. He is also a small-business owner in south India.

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This suitcase-lift alarm circuit uses vibration sensor HDX-2NC instead of a commercially available sensor. A home-made mercury switch can also be used instead.

Suitcase-lift alarm circuit

Circuit diagram of the simple suitcase-lift alarm is shown in Fig. 1. It is built around HDX-2NC, which is connected across connector CON2, transistors BC547 (T1) and BC557 (T2) and a piezo buzzer (PZ1).

Circuit diagram of the simple suitcase-lift alarm
Fig. 1: Circuit diagram of the simple suitcase-lift alarm

Normally, vibration sensor terminals are shorted internally. When the suitcase is lifted, sensor terminals momentarily open. This allows capacitor C1 to charge through resistor R1 and diode D1. Discharging path is through VR1 and T1.

parts list

When T1 and T2 conduct due to charged C1, LED1 glows and the buzzer sounds. Alarm duration can be set using VR1.

Use a piezo buzzer with internal oscillator for the alarm sound. The circuit works off a 9V battery, which is connected across connector CON1.

Construction and testing

A single-side PCB pattern for the simple suitcase-lift alarm is shown in Fig. 2 and its component layout in Fig. 3. After assembling the components on the PCB, house the circuit in a small box.

Fig. 2: A PCB pattern for the simple suitcase-lift alarm
Component layout of the PCB
Fig. 3: Component layout of the PCB

Download PCB and component layout PDFs: click here

Check the circuit’s working before you put it in your suitcase for use as an alarm. Switch on the circuit and place it in a suitable place inside your suitcase.


 

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10 COMMENTS

  1. good day sir,
    I like this circuit set up and would like to try it.
    how can the sensitivity triggering the alarm be increased or decreased?

  2. Thanks for the feedback! The sensitivity depends on the sensor used here. In this example, the sensitivity cannot be increased or decreased with the current design.

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