When it comes to magnetic switches and sensors, there hasn't been much new since the reed switch was invented in the 1950s. But reed switches used for security on doors and windows can easily be defeated with a simple magnet. The Magnasphere switch from Magnasphere Corp., Brookfield, Wis. (www.magnaspherecorp .com), uses an elegantly simple design to overcome this limitation. The switch consists of a spherical magnet inside a small metal housing. When a sufficiently strong magnetic influence enters the switch's 60° sensing zone, it pulls the sphere into contact with the housing and electrode, completing the circuit. When the magnet is removed, the ball jumps to the switch's ferrous cap, breaking contact with the electrode and opening the circuit. The switch can be used as security device, a ferrous metal detector, a tilt sensor, or a replacement for Hall sensors.
The spherical magnet is gold plated, and the patented switch is hermetically sealed in an inert atmosphere. It requires no power, lasts at least 3 million cycles with a signal-level load, and is unaffected by EMI or even a 500,000-Vdc shock from a stun gun. The all-metal switch can also be installed using automated PCB techniques, including surface-mount technology and wave soldering. It measures 0.24 in. in diameter, 0.175-in. high (without lead), and has an electrode pin with a 0.02-in. diameter.