Hello. this is my first time posting on this forum. let me start by saying that I am a total novice. I am trying to help out my 7 year old son.
he has a "treasure chest" where he keeps his "treasures" some old coins and trinkets from family trips. well, he wants to add an alarm to the chest, that will alert him if someone opens it. I think it is great that he wants to dabble in electronics. so, I want to help him however I can. He needs something to know when the circuit is broken to trigger a buzzer.
he has a battery pack (3 x AA) and a small 1.5-3v buzzer from an old toy that he wants to use for the alarm. he got a small circuit board and some wire from a trip to Radio Shack with his mother. I have an old soldering iron from my dad and can help him solder. We have a RadioShack not too far away, so we can get whatever parts are required.
so, now I need to know what kind of circuit he needs to create. I have searched the internet over the past few nights but can't seem to find anything simple enough for a 7 year old and his novice dad to understand.
I hope to help him succeed in hopes it might spur on an interest in electronics.
so, if anyone can point me somewhere or give me some Electronics for Dummies help, it would be greatly appreciated.
Thanks in advance for any help!
Jim

 

try this. it's simple and efficient. when the lid is closed, it will push the springy metal down and open the circuit. battery will stay charged indefinately; no drain on it. when the lid is opened, the metal will lift up and contact the metal tab (bottom right) and sound the alarm

 

You only need a switch. You can use a switch like this:

http://www.radioshack.com/product/index.jsp?productId=2049718

Use the common (C) and normally closed (N.C.) contacts. Mount the switch near the edge of the box that opens. You might have to add a small tab to the lid to actuate the switch. Everyone else made a drawing so I guess I have to also. Here it is.

 

Although not full-proof, this would be simple.

R2 should be 180 ohms, not 680 ohms.

Or for your simplicity, a kit such as one of the following.

Light Activated Alarm 1

Light Activated Alarm 2

 

@Ionic : If a looter were to come for the booty, they may well do so under the cloak of darkness....

 

@Ionic : If a looter were to come for the booty, they may well do so under the cloak of darkness....

...and take the chest, alarm and all!

But I second the suggestion of the lever switch OR a reed switch with a magnet to hold it closed when the chest is closed. That's how home security systems detect open doors or windows, or how the kid's bike detects speed, if it has a speedometer. It's a neat thing to learn about.

 

...and take the chest, alarm and all!

so maybe 2 seperate alarms. one inside the chest and another "indianna Jones" style alarm for if the chest is lifted

 

@Ionic : If a looter were to come for the booty, they may well do so under the cloak of darkness....

But if they want to see what "boot" (loot) they are stealing then a flashlight would be involved!

so maybe 2 seperate alarms. one inside the chest and another "indianna Jones" style alarm for if the chest is lifted

Please, have some pity on the Dad, the boy is only seven. How big is this chest anyways? A picture or description might be helpful.

 

Thank you all for the information and suggestions. We will talk it over and see what approach he wants to take. I hope this spurs on his interest. Best to all of you...

 

Since this is a father and young son project I really would recommend strantor's idea. Not only is it simple and can be made from stuff already around the house it shows how a switch works. A micro switch is great, but a loop of metal teaches how a switch works!

Reminds me of when I was 7 or 8 and made a night light for my tree house out of a battery, a bulb, some wire, thumbtacks and an old door key all on an old piece of wood. I used the thumbtacks and the key to make a switch which completely floored my mom.

Now I'm doing stuff like this, designed as a fridge door alarm. It senses light and beeps when it sees some:

Could you make it simpler? That's only 5 parts, runs for years off a coin cell as it doesn't use current when not sensing light (that ISCP doesn't count as a part as it is just connection points to program the PIC).

(I'm completely NOT suggesting this for NovicedDad)

 

I like the homemade switch idea for the same reasons but unless it's partitioned from the contents of the box, the mechanical interference will readily defeat it.

Ted Kaczynski (The Unabomber) made his own switches.

 

Ted Kaczynski (The Unabomber) made his own switches.

I can only hope that some day people will say "strantor made his own switches" .... but not for the same reason as ted kaczynski

 

I like the homemade switch idea ...

I'm leaning this way, too, now that I think about the son being 7, not in 7th grade. Just learning that metal is a conductor is important, and all the concepts needed to understand how it works are easily visible. A microswitch might teach how the job gets done in the "real world", but could be a bit of black-box magic to a 7-yr-old. Not to underestimate 7-yr-olds, but it's important to learn one step at a time, and to have fun doing it.

 

try this. it's simple and efficient. when the lid is closed, it will push the springy metal down and open the circuit. battery will stay charged indefinately; no drain on it. when the lid is opened, the metal will lift up and contact the metal tab (bottom right) and sound the alarm

There ought to be a way to disarm it so that little Johnny can not get buzzed himself.

I still don't know how big the box is...

 

I suggest inserting a peg (like a key) thru a small hole to disarm by obstructing the spring from moving.

 

I'm still a but skeptical about the spring mechanism as it could become misshapen or obstructed by objects in the box, even worse, metal objects.

 

I just wanted to post the circuit I thought of for this.

View attachment secretboxalarm.bmp

 

I just wanted to post the circuit I thought of for this.

Yes, a NC switch is what I've been trying to work into it.
For a secret enable/disable switch(Key!) you could use a DC power plug and it's female counterpart.

And the simplest way to stop the looter from taking the box is to velcro it down....that will wake up anyone!!!

 

Yes, a NC switch is what I've been trying to work into it.
For a secret enable/disable switch(Key!) you could use a DC power plug and it's female counterpart.

And the simplest way to stop the looter from taking the box is to velcro it down....that will wake up anyone!!!

Thats acctually a brilliant idea I must engineer something similar ...

 

Thats acctually a brilliant idea I must engineer something similar ...

I'm not sure if these part have a NO contact that closes with insertion, but the stereo 1/8 in. headphone jacks do.