The **WJM-151-R** is a specific model of an **electromagnetic buzzers** (also known as a magnetic transducer or sounder). These components are widely used in consumer electronics, medical devices, and industrial alarms to provide acoustic feedback. --- ## 1. Technical Specifications The "R" suffix typically denotes compliance with **RoHS** (Restriction of Hazardous Substances) standards. Below are the standard electronic characteristics for this part: | Parameter | Value (Typical) | | :--- | :--- | | **Type** | Magnetic / Electromagnetic | | **Rated Voltage** | 1.5V - 12V (Model dependent, usually 1.5V) | | **Operating Voltage** | 1.0 ~ 2.0 VDC | | **Rated Current** | Max 30mA | | **Sound Pressure Level (SPL)** | Min 80dB at 10cm | | **Resonant Frequency** | 2000Hz - 2400Hz | | **Operating Temperature** | -20°C to +70°C | | **Terminal Type** | PCB Pins (Through-hole) | --- ## 2. Internal Electronic Structure The WJM-151-R operates on the principle of electromagnetism. It consists of the following internal parts: * **Coil:** A winding of fine copper wire that generates a magnetic field when current passes through it. * **Magnet:** A permanent magnet that interacts with the field created by the coil. * **Vibrating Diaphragm:** A metal disk (usually iron or steel) that is pulled toward the electromagnet and released rapidly, creating sound waves. * **Housing:** A plastic casing (often NORYL or PBT) designed to act as an acoustic resonance chamber to amplify the sound. --- ## 3. Driving Circuitry Unlike "Active Buzzers" which beep as soon as DC power is applied, the **WJM-151-R is typically a Passive Transducer**. This means it requires an external oscillating signal (square wave) to function. ### Typical Connection Diagram ```cpp // Example Arduino-style pseudo-code to drive the WJM-151-R void setup() { pinMode(9, OUTPUT); // Connect Buzzer to Pin 9 } void loop() { tone(9, 2400); // Send 2400Hz square wave delay(500); // Beep for 0.5 seconds noTone(9); // Silence delay(500); } ``` --- ## 4. Key Application Use-Cases * **Household Appliances:** Beeping sounds on microwave ovens or washing machines. * **Portable Devices:** Low-voltage alerts in battery-operated handheld tools. * **Computers:** Motherboard "POST" code error beepers. * **Security:** Keypad entry confirmation sounds. ---