Troubleshooting and repairing Switch Mode Power Supplies

Laser Light Security Alarm

The aim of this article to make a laser light security alarm and it can also be used as a home security system. The essence of this project is that anyone can make it at home to save their home from thefts.


  • Soldering iron
  • Soldering flux
  • Solder wire
  • Small hand drill machine

Components Required

  • Plain PCB (printed circuit board)
  • Scrubber
  • PCB etching
  • Double-sided tape
  • Resistor 100 Ω – 03nos.
  • LDR (light dependant resistor)-01no.
  • LED (light emitted diode)-01no.
  • Transistor (BL548) -02 nos.
  • Buzzer
  • Switch
  • DC socket (Nokia cellphone small charging pin)
  • Adapter -5volt (nokia charger)
  • Battery holder
  • Battery
  • Laser light
  • Switch

Construction & Testing

Step 1

Tracing the circuit

Take a permanent marker and make a rough layout or path draw on your PCB as shown in figure 1.

Fig. 1: Layout or path draw of the PCB
Fig.2: Laser Light Circuit
Schematic Circuit diagram of the laser light security alarm system
Fig. 3: Schematic Circuit diagram of the laser light security alarm system

Step 2

Clean the PCB with the help of a scrubber and after taking a small size container and some PCB etching solution (Ferrous Chloride), prepare a solution of etching by mixing the ferrous chloride and water in a container. Dip PCB into solution and shake it for 10 minutes, now take out the PCB and wash it thoroughly.

Step 3

Drill few holes on PCB with the help of small hand drill for mounting other electronic components.

Find the location of electronic components from layout and placing them carefully on their respective positions.

Solder the electronic components on PCB and assemble the laser light and solder it carefully with the battery holder and also solder a switch to positive terminal of battery holder.

Step 4

Final step

Carefully placed the battery holder and after checking the output voltage of circuit with a multimeter.

After checking the circuits again for proper placement, press the switch ‘ON’.

Now, when you put your finger in front of laser, you will find that the buzzer would turn on thus producing an alarm. When you ‘OFF’ the switch the buzzer will not make any sound.

Your Security System is ready.

Shri Himadree Bhusan Sahoo is an Electrical Engineering student and Electronics Enthusiasts

This content was originally published here.

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