Summary of Building a Sentry Gun with Laser Trip Wire System and Arduino
This article details a student project from Singapore Polytechnic to build a laser-triggered toy gun sentry system. The device uses an Arduino, laser sensors, and servo motors to detect intruders and fire a semi-auto toy gun. Construction involves basic soldering and metalwork, utilizing a custom frame made of cut metal sheets, ball bearings for pivoting, and various electronic components like LDRs, transistors, and resistors.
Parts used in the Laser-Triggered Toy Gun Sentry:
- Toy Gun (preferably semi-auto)
- Continuous Rotation Servo Motor
- Servo Motor
- Servo Arms and Wheels
- Arduino
- Metal Sheets
- Ball Bearings
- Bolts
- Nuts
- Screws
- Rubber Washers
- Cable Tie
- Copper Wire
- Copper Strip Board
- Pins
- Sockets
- Resistors (1K Ohm)
- Light Dependent Resistor
- Potentiometer (20K Ohm)
- NPN Transistor (2N2222)
*NOTE* THIS PROJECT IS DONE BY A GROUP OF STUDENTS FROM SINGAPORE POLYTECHNIC.
Concept:
Trigger gun when laser is blocked by intruding object.
Note:
Tilting is included for expandability but not used in this project.
Skill Level:
Basic soldering and basic metal works
Things You Need:
Toy Gun(Any will do, preferably a semi-auto)
Continuous Rotation Servo Motor
Servo Motor
Servo Arms and Wheels
Arduino
Metal Sheets
Ball Bearings
Bolts
Nuts
Screws
Rubber Washers
Cable Tie
Copper Wire
Copper Strip Board
Pins
Sockets
Resistors(1K Ohm)
Light Dependent Resistor
Potentiometer(20K Ohm)
NPN Transistor(2N2222)
Step 1: Building the Frame
Cut the metal sheets into 6 rectangular pieces(4 of equal length, 1 long, 1 short) and 2 square pieces.
Below are the dimensions we used:
4x 6”(inch) by 2”
1x 10.5” by 2.4”
1x 2.5” by 2.4”
1x 10” by 10”
1x 9” by 9”
Feet(6” by 2”):
Bend the 4 metal piece 90 degrees at the 2” mark and make screw holes(at least 2) at the shorter end.
[Image 1]
Base(9” by 9”):
Make screw holes that match your feet’s at 4 corners of the metal piece to mount the feet and a hole in the center for the pivot(the hole size depend the bolt you’re using).
[Image 2]
Gun Support(10.5” by 2.4”):
Bend the metal piece 90 degrees at the 2” mark and the 6.5” mark to form a deformed U. Make screw holes(at least 2) at shorter end and 4 holes at the other end to mount your servo.
[Image 3]
Turning Panel(10” by 10”):
Make screw holes that match the gun support’s at one corner of the metal piece and one hole in the center for the pivot(should be slightly larger than the pivot but smaller than your ball bearings).
[Image 4]
Servo Mount(2.5” by 2.4”):
Make a hole at one end to fit into the pivot and 4 holes at the other end to mount your servo.
[Image 5]
Step 2: Trigger of the Gun
Mount one of the servo to trigger the gun
We secure a small servo with a short servo arm onto toygun.
Step 3: Putting Everything Together part 1
Mount the gun onto a continuous rotation servo[Image 1].
Secure it onto the gun support[Image 2 & 3].
Secure another continuous rotation servo with wheels[Image 4] onto the servo mount[Image 5 & 6].
For more detail: Building a Sentry Gun with Laser Trip Wire System and Arduino
- What is the main concept of this project?
The concept is to trigger a gun when a laser is blocked by an intruding object. - Can tilting be used in this project?
Tilting is included for expandability but is not used in this specific project. - What skill level is required to build this?
Basic soldering and basic metal works skills are required. - How many rectangular metal pieces are needed for the frame?
You need 6 rectangular pieces consisting of 4 equal length, 1 long, and 1 short piece. - Which transistor model is specified for the circuit?
The NPN Transistor model 2N2222 is specified. - What type of toy gun is recommended?
A toy gun that is preferably semi-auto will do. - How is the turning panel dimensioned?
The turning panel is made from a 10 inch by 10 inch metal sheet. - Does the project require any specific resistor values?
Yes, it requires 1K Ohm resistors and a 20K Ohm potentiometer.
