The **MEWT-21D-R** is a specific model of an **Electromagnetic Transducer (Buzzer)**. These components are widely used in consumer electronics, medical devices, and industrial equipment to provide audible feedback or alarms. Below is a detailed breakdown of its electronic characteristics and specifications. --- ## 1. Core Technical Specifications The MEWT-21D-R is designed for high-reliability applications requiring a clear, consistent tone. | Parameter | Typical Value | | :--- | :--- | | **Type** | Electromagnetic Transducer | | **Rated Voltage** | 1.5V DC | | **Operating Voltage** | 1.0 ~ 2.0V DC | | **Rated Current** | Max 40mA | | **Sound Pressure Level (SPL)** | Min 85dB (at 10cm) | | **Resonant Frequency** | 2,730 Hz | | **Coil Resistance** | 16 ± 3Ω | | **Operating Temperature** | -20°C to +70°C | --- ## 2. Key Electronic Components & Construction The device functions through the interaction of several internal parts: ### A. The Magnetic Circuit * **Permanent Magnet:** Provides a static magnetic field. * **Electromagnetic Coil:** When an oscillating current passes through this coil, it creates a fluctuating magnetic field. * **Iron Core:** Concentrates the magnetic flux to increase efficiency. ### B. The Vibrating Element * **Vibrating Diaphragm:** A thin metal plate (usually iron or an alloy) that reacts to the magnetic fluctuations. As the magnetic field changes, the diaphragm moves back and forth, pushing air to create sound waves at the **Resonant Frequency (2,730 Hz)**. ### C. Housing and Terminals * **Case Material:** Usually PBT (Polybutylene Terephthalate) or similar high-heat plastic to withstand soldering. * **Pins (R-Type):** The "R" in the model name often refers to the pin configuration or "Rear" entry for specific mounting styles (Through-hole PCB mounting). --- ## 3. Driving Circuit Requirements Unlike a "Piezo Indicator," the MEWT-21D-R is a **transducer**, meaning it does **not** have an internal oscillating circuit. You cannot simply apply a flat DC voltage to make it sound. 1. **Oscillation Source:** You must provide a square wave signal at the resonant frequency (approx. 2.7 kHz). 2. **Driver Circuit:** Since it draws up to 40mA, it is recommended to use a NPN transistor (like a 2N2222) to drive the buzzer from a microcontroller (MCU) pin. 3. **Flyback Diode:** It is highly recommended to place a diode in parallel with the buzzer to protect the circuit from inductive voltage spikes when the coil is switched off. ### Basic Driver Example ```cpp // Example: Driving with an Arduino-like MCU int buzzerPin = 9; void setup() { pinMode(buzzerPin, OUTPUT); } void loop() { // Generate a 2730Hz tone tone(buzzerPin, 2730); delay(500); noTone(buzzerPin); delay(500); } ``` ---