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The idea for this project came to my mind when my whife bough a torch for our 5 year old son. The torch has a bendable "neck" and a magnet. With the ,agnet my son can place the toch on metal things. The light beam could be changed to a 90 degrees angle.
My son ran through the house, placed the torch here and there and said ".. this is a trap for burglars .." by letting the torch send a light stream across the room.
This made me think of a photo sensor to build a "real trap for burglars".

Step 1: Planning

The following guidelines should be applied to the project:
- easy to use for my son
- powered by battery
- work with minimum power consumption
- audible alarm
- don't buy anything! Everything should by surplus material

I searched around an found an old photo sensitive transistor mounted on a pice of plasic together with a small resistor. The transistor had BPY 62 III written on it.
First I thought of building a schmitt trigger using an op amp. Then I saw in one of my old electronic books a principle circuit diagram of a shmitt trigger build with transistor.
I decided to use a 9V block cell battery as a power source. For the audible alarm I used an piezo electirc signal generator. The schnitt trigger needs a current of about 11 mA to flow through the collector. The piezo electric element does not generate this much current. To make the circuit work I put an led in parallel to the piezo. This way I got a visible alarming to.

Step 2: Building and Testing

The whole thing was build without pcb. I just connected all the components.
After a short test I began putting all the stuff into the Pringles box.
I cut the wooden ballpen to a length exactly the diagonal dimesions of the round of the box. I made a small hole into the box. I sew a small gap into the ballpen to put the phototranssitor in it. The I glued the pen into the box. I put some insulating tape on the wires of my circuit and thre it into the box.

That's it. Watch the video to see how it works ...
A small 9V block batterie feeds the circuit. I also put a small switch into the box so that my son can switch the device on and off.


i made a counter and a kind of buzzer with pic16f628a :)
Cool!! are you a schreck? I was searching for something else when I found this...
yay for pringles my favourite food!!!
Gotta love Pringles!
pringles and koolaid are good
not me real drink koolaid
sorry i dont have it any more ill try to make another :)
I made an alarm out of an old "security camera" that set off a series of disposable camera flashes and a car horn.
Do you have an instructable of this? I like to know more about the project.
Ok, to make one thing clear. I don't like to use that TOY as a real alarm. I made this for my little son to play around with it. I don't like to get him deaf by the alarm. I just want him to have some fun. If I made a reals alarming system I would do that with other type of sensors and a microprocessor controlled alarming central ... But let me finish my remote swith for a digitally controlled window shutter first ;-)
You may want to change the word "torch" to "flashlight" or something in the Intro... people could get the wrong idea... :-) Nice though!
Hi, thank you for the hint. I'm german and I learnd british in school. In american english it is called flashlight. Hearing the word flashlight I always think of photo flashlights. Maybe I should use both words ...
The alarms a little quite so its not gunna help you against robbers ;). Try to get the alarm LOUDER...
Very Nice! I wonder ifyou could intagreate a 433mhz TX/RX or somthing to that affect to alert you id the trap went off. I dont know how this would work but it would be cool if you could use IR leds insted of a "real light"

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