In this instructable I am going to show you how you can make magnetic switches that can be used to activate a circuit just like a regular momentary switch.
Step 1: How It Works
Many electrical devices use momentary switches. They are most commonly used to set a logical HIGH or LOW state that is read by a microprocessor/integrated circuit. When working with momentary switches, you can wire multiple switches in parallel to create an OR gate. This lets any of the switches activate the device just like the original would. A magnetic reed switch can be used in this way so that the circuit can be activated by a magnet as well as the button. When a magnet is brought close to the sensor, two metal contacts inside the reed switch are pulled into contact with each other. This contact acts like a switch and activates the circuit.
Warning: Be aware that some electronics can be damaged by magnets. Keep magnets away from sensitive electronics such as cathode ray rubes (CRT's), magnetic recording devices, etc.
Step 2: Materials
To make an auxiliary magnetic switch, you will need the following:
Magic Wand Prop
Magnetic Reed Switch (Normally Open)
Small Strong Magnet (preferably rare earth)
Soldering Iron and Solder
Step 3: Purchase or Make a Magnetic Reed Switch
You can purchase magnetic reed switches from a number of online retailers such as Radio Shack, Digi-Key or Mouser. They are often sold as door/window sensors for security systems.
You can also make them with a small piece of steel wire such as a paper clip. To do this, cut off one piece of wire that is about 1/2 inch long and one piece of wire that is about two inches long. Solder them both to a PC board and bend the longer piece over so that it crosses the shorter piece. Position them so that they are almost touching. When a magnet is brought close to the wires, the longer piece will be pulled into the shorter piece and the two will make contact. You can make this kind of switch more sensitive by making the bent wire longer. You can also increase the amount of metal at the end by folding the wire back onto itself several times.
Step 4: Find or Make an Appropriate Magic Wand
You can purchase toy wands. But it is much fun to make your own. There are many different styles of wand to choose from. You can make a traditional magician's wand that is a black rod with white ends. You can make a wizard's wand like the ones seen in Harry Potter. Theses are typically wooden dowels that are tapered to a point at the end and may have details carved into the handle. Lastly, there is the fairy princess wand. These can be a simple rod with a heart or star on the end or they can be completely covered in jewels, glitter and streamers. The choice is up to you. If you do decide to make one, here are some links that you may find helpful.
Step 5: Attach Your Magnet to the Wand
Once you have a wand, you need to embed a magnet into the end of it. How you do this will depend on the kind of magnet that you have as well as style of wand that you want to make. For a wand that has a tip that is covered in fabric, you can just fit it anywhere inside the fabric. The easiest thing to do is to remove the rod, tape the magnet to the end of the rod and reattach it.
If you are making a wizard's or magician's wand, try to find a suitable magnet that it smaller than the tip of your wand. Then drill a hole or cut a slot that is the same size as the magnet in the end of the wand and glue the magnet into the hole. Feel free to use whatever method that you find works best.
Step 6: Wire the Magnetic Reed Switch in Parallel to the Original Switch
Open up the housing of your electrical device and locate the switch that controls the function of interest. Observe how it is wired to the rest of the circuit. If the switch has more than two terminals it may be necessary to use a multimeter to determine which terminals are connected to each other when the switch is pressed.
Once you have determined which terminals on the switch are connected when the switch is pressed (but are not connected when the switch is not pressed), then you are ready to attach your magnetic reed switch to these terminals. Solder one lead of magnetic reed switch to one of these terminals and solder the second lead of the reed switch to the other terminal.
Step 7: Attach the Reed Switch to the Outer Housing
Next you need to find a place to mount the reed switch. Try to find a location on the inside of the housing that is relatively unoccupied. It should also be easy for you access with on the outside of the housing with the wand. Hold the reed switch in the desired location and touch the wand to the opposite side of the housing. If the circuit activates, then it is a suitable location. Tape or glue the reed switch in place and reassemble the housing.
Step 8: Use Your Magic Wand to Activate Your Circuit
Now all you need to do is give the wand to an imaginative young child and watch them be amused at how they can use it to turn on electronics "like magic."
Step 9: Possible Design for Use With Latching Switches
You can also create this kind of reed switch circuit for devices that use latching switches instead of momentary switches. However, it is a little more complicated and requires more parts. Here are two examples of how you could make latching relay circuits with reed switches.
Wiring either of these circuits in parallel with a latching switch will create the same kind of OR gate. It is different in that the switches stay active and the device will only deactivate when both switches are in the off position.
You could also wire these circuits in series with the device. This would require you to leave the original switch in the on position. The benefit of a series switch is that it could be located in a separate housing. You could make a separate adapter that you could just plug any a device into without having to modify the internal circuitry.