Thread: Simple switch project - help an electronics newbie!

Hi there,

I have a personal project that Im after a bit of help with but before I start, I must let you know I am a complete electronics n00b - I literally know nothing about what I am asking!What I am trying to construct is a small box with a magnet in it, which when removed from another magnet will set off an alarm and flashing light.

The trigger does not necessarily have to be magnetic - if there is another way to set off the alarm by simply lifting the box off the surface that is fine!

Apologies for my electronic ignorance - any help on what bits and pieces I could buy to construct this would be much appreciated!*Thanks a lot!

Hi, you can get magnetically operated switches. You might want to get a catalogue from your local electronic parts supplier (I can't recommend a shop as I don't know where you are). Look for reed switch or magnetic switch (these are used on windows in burglar alarms, for example). This is probably the simplest method.

There are various other ways of detecting nearby objects so you could look for proximity sensors to see if there is anything useful.

The other possibility is purely mechanical: a small rod/button which protrudes (from the box or the surface) that is allowed to move when the box is lifted. Look for microswitch.

Finally, if the switch is intended to be in the box (rather than the surface) then you could look for a tilt or mercury switch which will detect if the box is tilted.

There are also accelerometers; which are purely electronic devices which detect motion (these are what are used in things like Android phones or iPads to detect motion and orientation). These probably require more complex circuitry than you want.

Thanks a lot - I will look for a magnetic switch.. Any ideas as to where I could buy a flashing light and alarm to connect to the switch?

Would it be possible to connect this to a magnet switch? How would I do that?

EDIT; Just realised below wouldn't be appropriate - requires 12V. Really am after something 9V...

Wired External Outdoor Large Siren with Red Strobe Rotate Light | eBay

Depends where you are. In the UK, Maplin sell this sort of thing - online.and branches everywhere. In Japan, Tokyu Hands. In the US ... Frys? Target? dunno, been away too long...

In the US, Radio Shack, or an Ace hardware store might carry things like this.

Smoke detectors have 9 volt batteries, and make a nice loud noise. If you take the cover off a smoke detector, you will see that there is a test pushbutton, which is probably just a metal bar that touches another metal object when the button is pressed. All you have to do is solder one wire to the bar and one to the metal object it contacts, and then connect these wires to your alarm switch.

For an alarm switch, a burglar alarm type should work. Make sure you get one that is normally open.

SECO-LARM SM-300Q/WH Surface Mount Magnetic Contact Switch, Normally Open - Smarthome


Here's another idea. A personal alarm that sounds when a metal chain is pulled out. No wiring needed.

http://www.tbotech.com/door-knob-alarm.htm