Description
The MC-38A is a surface-mount magnetic reed switch designed for door and window status detection in DIY electronics, smart home projects, and basic alarm systems. As a Normally Open (NO) sensor, its circuit remains open (non-conductive) when the magnet is near the switch body—meaning when the door or window is closed, the circuit is broken. When the door or window opens and the magnet separates from the switch, the circuit closes, allowing current to flow and triggering the connected alarm panel or microcontroller to register an event . This behavior is the opposite of the Normally Closed (NC) MC-38 variant, which is preferred for fail-safe security systems. The NO configuration is better suited for simple Arduino logic where an open door should produce an active HIGH signal, or for applications where a closed circuit on intrusion is acceptable. The MC-38A consists of two components—the reed switch body and a matching permanent magnet—both housed in compact ABS plastic enclosures measuring approximately 27 × 14 × 8 mm . It requires no external power supply and functions as a passive switch, connecting directly to a microcontroller GPIO pin with an internal pull-up or pull-down resistor. The sensor is suitable for wooden and plastic door/window frames, and is not recommended for iron or steel surfaces, which can interfere with the magnetic field .
Features
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Normally Open (NO) Contact Type: Circuit closes only when the magnet is removed (door/window opened), producing an active signal on intrusion—ideal for simple trigger logic in Arduino projects .
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Passive, Power-Free Operation: Requires no battery or external power; the reed switch is actuated solely by the magnet’s proximity.
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Compact Surface-Mount Design: Slim ABS housing (approx. 27 × 14 × 8 mm) installs discreetly on frames using screws or double-sided adhesive tape .
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Wide Actuation Gap Tolerance: Reliable switching across an operating distance of approximately 15–25 mm, accommodating imperfect alignment during installation .
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Wired Connection for DIY Electronics: Pre-attached wire lead (approx. 30 cm) connects directly to microcontroller GPIO pins or alarm panel zone inputs .
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Durable ABS Construction: White plastic housing resists wear and deformation for long-term reliability in residential installations .
Technical Specifications
| Parameter | Specification |
|---|---|
| Model | MC-38A |
| Contact Type | Normally Open (NO) |
| Switch Element | Magnetic Reed Switch |
| Housing Material | ABS Plastic (White) |
| Operating Voltage | Up to 100V DC (max) |
| Rated Current | 0.5A max |
| Contact Power | 10W max |
| Actuation Distance | Approx. 15–25 mm typical |
| Wire Lead Length | Approx. 30 cm |
| Housing Dimensions | Approx. 27 × 14 × 8 mm |
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