Reed Switch Module KY-021

Description

The Mini Reed Switch Module activates a switch closure when a magnetic field comes near.

Key Features of Mini Reed Switch Module:

• Outputs logic HIGH or LOW depending on if a magnetic field is near
• Built-in 10K pull-up resistor
• 3.3 and 5V compatible

Reed switches are mechanical switches that are activated by a magnet when the magnetic field pulls the metallic switch contacts together.  Real-world uses include applications such as home security where a reed switch is placed in proximity to a magnet when a window is closed.  If the window is opened, the magnet moves away from the switch which causes it to change states which can then be detected by an MCU.

This module is an SPST switch with NO (Normally Open) contacts until a magnet comes into proximity to the glass envelope and then the switch contacts are closed.  The output is HIGH when the switch is open and is grounded (LOW) when the contacts are closed.

Module Connections

There is a 3-pin header on the assembly.  The ‘-‘ pin is connected to the ground end of the switch and the ‘S‘ output pin is connected to the other side of the switch.  If an ohmmeter is placed between these two points, the switch will read open.  If a magnet is placed close to the glass envelope, the switch will close and the meter will read close to 0 ohms.

There is a 3rd unmarked pin in the center that connects to a 10K pull-up resistor.  You can either tie this pin to Vcc so that the pin will be pulled HIGH when the switch is open or you can enable an internal pullup on the pin that connects to the MCU.

1 x 3 Header 

• ‘-‘ = Ground
• Center pin = No connection or VCC
• S = Signal output connects to a digital input pin on MCU

Technical Specifications: