i will show you how to make a laser powered burglar alarm
Step 1: Materials Required
3] coin cell - cr2032
4] one laser 2mv or more (most important =D)
5] pref board or bead board or you can do it without using both
6] foam (for the stands)
7] 2n2222 transistor
7] resistor 100 ohm and 4.7k ohm
8] Two Neodymium (NdFeB) magnet
9] metal strip
10] tape and double sided tape
11] a long nail or toothpick
Step 2: The Circuit Digram
solder the components according to the circuit digram
the transistors back is facing you.
Step 3: How the Circuit Works
The 4.7k ohm resistor acts as a sensitivity controller for the LDR
you can change it between 1k to 100k to change the sensitivity
for this circuit i recommend 4.7 or lower
Step 4: Solder the Components
Step 5: Make the Stand for the Laser
1] cut a small piece of foam
2] then cut a small slit kind of a thing as shown in the pics
3] pierce a toothpick to give stability
Step 6: Make the Stand for the Circuit
1] cut a small piece of double sided tape
2] stick it on the side of the door or where ever you kept your precious things
3] stick a metal strip on it
4] stick a magnet on the circuit board with the help of double sided tape
Step 7: Now Set Up the Alarm
both the metal strip and the foam piece should be parallel to each other.
now keep the laser on the slit in the foam piece and on it such that the beam falls on the photo transistor
when you will interrupt the beam a sound goes off
Step 8: Make It With a Phototransistor
you can make this circuit with a phototransistor
you will need
2] photo transistor [dont have one see next step i will show you how to make one]
3] 2n3904 transistor
4] coin cell
Step 9: Make the Photo Transistor
you will need
1] carbon tetrachloride
2] AC126 transistor
if you cant get a photo transistor you can make it with a AC126 transistor
first take a AC126 transistor and remove its metallic cap.then wash the inside with carbon tetrachloride till the white paste like substance is completely removed.Now cover the transistor with a transparent glass cap to protect it from moisture and damage.in this way your photo transistor is ready.
Step 10: Making It Simpler
if you are new at electronics you can make a simpler alarm.
Step 11: Video
see the circuit in action but with a torch as my laser broke when i bought it.
Step 12: The Video Link
Step 13: All Done
you burglar alarm is now ready use it to protect you precious things.
hope you like this instructable.
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