Step-by-Step Guide: Test MC-38 (NC) & MC-38A (NO) Magnetic Reed Switch with Arduino

Magnetic reed switches are simple, affordable, and extremely useful sensors for door/window security systems, Arduino projects, and smart home automation.

In this guide (based on the video), we’ll test two popular models:

✅ MC-38 = Normally Closed (NC)
✅ MC-38A = Normally Open (NO)

MC-38 (NC) VS MC-38A (NO) Magnetic Reed Switch with Arduino.

By the end, you’ll understand how each one behaves, how to wire them, and how they can be used in real projects like alarms and home automation.

Step 1: What You Need (Parts List)

To build the same setup from the video, gather these items:

🔧 Components

• Arduino Uno (or any Arduino board)

• Breadboard

• Jumper wires

• 2× LED (optional but recommended)

• 2× Resistor for LED (220Ω to 330Ω)

• 1× MC-38 (NC) reed switch

• 1× MC-38A (NO) reed switch

• Matching magnet pieces

Step 2: Specifications

The MC-38 and MC-38A look similar, but they have different contact types and electrical ratings. These specifications help you understand the safe voltage/current limits and ideal mounting conditions.

✅ MC-38A → Normally Open (NO)

✅ MC-38 → Normally Closed (NC)
✅ Operating Voltage: Up to 100V DC
✅ Rated Current: 0.5A Max
✅ Contact Power: 10W Max
✅ Actuation Distance: 15–25mm typical
✅ ABS Plastic Housing
✅ Cable Length: ~30cm

MC-38 & MC-38A key specifications and correct NO/NC contact type

Step 3: Understand NC vs NO

Before wiring, know the difference:

🧩 MC-38 = Normally Closed (NC)

• Default state: Circuit CLOSED

• When magnet moves away: Circuit OPENS
  ✅ Best for security systems (wire cut = alarm trigger)

MC-38 normal state circuit closed.

🧩 MC-38A = Normally Open (NO)

• Default state: Circuit OPEN

• When magnet moves away: Circuit CLOSES
  ✅ Best for simple Arduino logic (open door = ON trigger)

MC-38A normal state circuit open.

Step 4: Simple Project Wiring Setup

Now connect the sensors to Arduino using the wiring diagram shown in the attached image. This simple circuit allows Arduino to detect the sensor state and trigger LED indicators.

Simple Arduino wiring setup for MC-38A (NO) and MC-38 (NC) sensors.

Step 5 — Upload Arduino Code & Open Serial Monitor

You can download the code HERE. The sensor status is shown using:

✅ LED indicator
✅ Arduino Serial Monitor output

Serial Monitor output shows live sensor status while testing magnet distance.

What you do:

1. Upload your sketch (code)

2. Open Serial Monitor

3. Watch the value change as you move the magnet

Step 6: Test MC-38 (Normally Closed / NC)

Now test the MC-38 sensor (NC).

✅ Test Results:

MC-38 (NC) changes from closed to open when the door/window opens.

📌 Magnet close (door closed): circuit is CLOSED → reads LOW

📌 Magnet far (door open): circuit is OPEN → reads HIGH

✅ So when you open the door, the Arduino detects it instantly.

Step 7: Test MC-38A (Normally Open / NO)

Now test the MC-38A sensor (NO).

✅ Test Results:

MC-38A (NO) changes from open to closed when the magnet moves away.

📌 Magnet close (door closed): circuit is OPEN → reads HIGH

📌 Magnet far (door open): circuit is CLOSED → reads LOW

✅ This gives the opposite behavior from the NC version.

📦 Where to Buy

Shopee:

1. MC-38/MC-38A Sensor

Lazada:

1. MC-38/MC-38A Sensor

TikTok:

1. MC-38/MC-38A Sensor

Aliexpress:

1. MC-38/MC-38A Sensor

Final Conclusion

MC-38 (NC) and MC-38A (NO) magnetic reed switch sensors are simple, reliable, and perfect for security systems, Arduino projects, and smart home automation. Once you understand the difference between Normally Closed vs Normally Open, you can easily build door/window alarms, IoT sensors, and automation triggers.

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