A reed switch is an electronic device that closes a circuit when a magnet passes close to it. You have probably used devices that contained reed switches in your day to day life. Alarm systems use reed switches to tell if a door or window has been opened. A bicycle computer uses a reed switch to count the frequency of passes of a spoke mounted magnet to determine speed and distance. Once you start using them, you'll find hundreds of uses for reed switches.

In this instructable I will show you one way to make quick and dirty reed switches.

***Warning: The reed switches you make at home are vastly inferior to store bought. If you have a serious project that needs a reed switch i highly recommend you buy one rather than cobbling one together in your garage. I made this Instructable to demonstrate a concept but I will be the first to admit that the finished product is lacking in quality and reliability. With that said; lets make some switches!

We'll start with a parts list:

a 3" piece of copper pipe
a spool of steel craft wire (or) a small steel spring
some mini zip ties
a rare earth magnet
a sheet of 'Plastic Canvas'*
scissors

Plastic canvas is a plastic mesh used for some type of latch-hooking. It costs about $1 a sheet and is available at craft stores in the needle-art section. I've never done needle art but this is very handy stuff to have around. Plastic Canvas @ A.C.Moore

EDIT: I added an animation to show how a reed switch works. I just purchased some reed switches from Mouser so stay tuned for some upcoming reed switch based instructables.

Step 1: Make It!

1. Once you gathered your materials you should start by drilling a small hole near the end of the copper pipe. This hole will allow you to solder a wire to this side of the switch.

2. Next, cut a small piece of plastic canvas to insulate the spring from the pipe.

3. If you are not using an existing spring, wrap a tight coil of steel wire around a pencil or similar item to make a tightly wound steel spring.

4. Zip tie the spring to the plastic canvas.

5. Insert into the pipe.

6. Attach a wire to the spring and one in the hole drilled in the copper pipe.

When the magnet comes close to the top of the pipe the spring gets pulled over and makes contact with the copper pipe

When the magnet is removed, the spring goes back to the rest position cradled in the plastic canvas insulation.

Congratulations, you just made a quick and dirty Reed Switch!

Please leave (constructive) comments if you have ideas to make this better.