Home > Circuit Bricks > Reed Switch
UPDATED:.21:11 21 October 2013

  • A Reed Switch is activated by magnetism, either from a permanent magnet or an electromagnet.
Reed Switches can switch on low power devices directly, such as LEDs, buzzers. But for sensing it should be used as part of a potential-divider. In this way, the output it supplies to other circuits is always connected to +v or 0v, and never left floating (disconnected).

Supply voltage up to 18v. Current up to 50mA approx.


Circuit Diagrams

When a magnetic field activates the reed switch, a change of output occurs.

There are 2 ways to connect a reed switch in a potential divider. These are shown right and work exactly opposite from one another.

With the Reed at the top of the potential divider, when the reed switch is activated, a high pulse is created. With the Reed at the bottom of the potential divider, when the reed switch is activated, a low pulse is created.
  • The reed switch is often made from glass so take great care when connecting to it.
  • Use a pair of pointed pliers if you have to bend the legs at all.
  • Do not overheat the reed switch too much when soldering.
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Written by Phil Townshend - 2008
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