MC-38 Wired Door Window Sensor Magnetic Switch Home Alarm System

Prototyping and Engineering Tips from Robogears

• Understanding NO vs. NC: The MC-38 is typically Normally Closed (NC), meaning the circuit is closed (conductive) when the magnet is near the sensor. When the door opens and the magnet moves away, the circuit breaks. In your code, use INPUT_PULLUP to detect this state change reliably without floating pins.

• Alignment is Crucial: For the most reliable trigger, ensure the two parts are aligned parallel to each other. If the magnet is offset or placed at a 90-degree angle, the detection distance will drop significantly, leading to "false alarms."

• Magnetic Interference: Do not mount the sensor directly onto ferrous metal surfaces (like iron or steel doors) without a non-metallic spacer. The metal frame can "bleed" the magnetic field away from the sensor, causing it to stay open or closed regardless of the magnet's position.

• Security Loop Tip: When building a home alarm, wire multiple MC-38 sensors in series. If any single door or window in the loop is opened, the entire circuit breaks, triggering the alarm. This saves microcontroller pins and wiring complexity.

Package Includes

• 1 x MC-38 Magnetic Switch (Wired Sensor Part)

• 1 x Corresponding Magnet (Trigger Part)

Disclaimer

This sensor is designed for low-power signal switching. Never use it to directly switch 230V AC mains or high-current motors, as the tiny internal reed contacts will fuse together instantly.