KY-021 Mini Magnetic Reed Switch Sensor Module

KY-021 Mini Magnetic Reed Switch Sensor Module is an ultra-compact magnetic proximity detection breakout board featuring a miniature normally open (NO) glass reed switch and an onboard 10kΩ pull-up resistor. When brought into proximity with a permanent magnet or electromagnet, the flexible ferromagnetic reeds snap together, closing the circuit to provide an instantaneous digital active-LOW switching signal to microcontrollers.

Key Features:

• Hermetic Glass Reed Tube: Enclosed gold/rhodium plated reeds protected in an inert gas glass capsule ensure sparkless, oxidation-free contact.
• Integrated Pull-Up Resistor: Onboard 10kΩ pull-up resistor keeps digital output firmly at HIGH (VCC) until triggered by a magnet.
• Instant Digital Active-LOW Signal: Delivers clean TTL-level switching transitions directly to microcontroller digital GPIO inputs.
• Compact Mini Footprint: Smaller footprint than comparator-based modules, fitting into the tightest door frames and enclosures.
• Zero Passive Power Consumption: Consumes practically zero operating power during static open/closed states.
• Standard 3-Pin Interface: Compatible with 3.3V and 5V Arduino expansion shields and Dupont breadboard cabling.

Technical Specifications:

• Operating Logic Voltage: 3.3V to 5.0V DC
• Operating Current: ~0.5 mA when magnetic contacts are closed @ 5V DC
• Switch Type: Normally Open (NO) Single-Pole Single-Throw (SPST) magnetic reed switch
• Onboard Resistor: 10kΩ metal-film pull-up resistor
• Output Format: Digital TTL (HIGH when open, LOW when magnet is present)
• Switching Life: Exceeds 10 million cycles under rated electrical load
• Operating Temperature: -20°C to +85°C

Mechanical Specifications:

• Form Factor: Mini rectangular sensor module board
• PCB Construction: Double-sided FR4 fiberglass board with green solder mask
• Protective Tube: Glass switch mounted horizontally on the board
• Header Type: 3-pin male header with 2.54mm pitch
• Weight: Approximately 2.0 g

Dimensions:

• Overall Length: 25.0 mm
• Overall Width: 15.0 mm
• Overall Height: 6.0 mm

Pinout and Wiring:

• – (GND): Connects to microcontroller system power ground (0V)
• + (VCC): Connects to positive DC power supply (+3.3V to +5V DC)
• S (Signal): Digital output signal connected to microcontroller digital GPIO input

Datasheet Reference:

• Consult the miniature glass reed switch engineering datasheet and KY-021 schematic for magnetic field sensitivity (Ampere-Turns), contact bounce timing, and actuation distance tables.

Commonly Used in:

• Concealed door, window, and cabinet closure sensors in residential alarm systems
• Bicycle wheel speedometers and rotating motor shaft tachometer pulse sensors
• Water tank contactless float level switches in agricultural and hydroponic systems
• Contactless limit switches for 3D printers and CNC linear positioning rails

Applications:

• Magnetic door and window security switch
• Rotational RPM tachometer pulse counter
• Liquid level float switch detector
• Contactless machinery limit sensor
• Smart home automation intrusion trigger

Equivalent Models:

• KY-025 Reed Switch Sensor Module (dual analog/digital comparator variant)
• MC-38 Magnetic Door Contact Sensor
• Hamlin 59165 Subminiature Reed Switch
• Keyestudio Mini Magnetic Reed Sensor

Package Includes:

• 1 × KY-021 Mini Magnetic Reed Switch Sensor Module