The **HC-49N-R** is a specific type of quartz crystal unit used in electronic circuits to provide a precise frequency for timing, synchronization, and clock generation. --- ### 1. Key Characteristics The part number suffix and prefix generally indicate its physical and mechanical properties: | Feature | Description | | :--- | :--- | | **Component Type** | Quartz Crystal (Resonator) | | **Package Style** | HC-49/U (Standard High Profile) or HC-49/S (Small/Low Profile) | | **Suffix "N"** | Usually denotes a specific lead configuration or mechanical height. | | **Suffix "-R"** | Typically indicates **RoHS Compliance** (Lead-free). | ### 2. Physical Construction The HC-49N-R consists of several internal and external parts: 1. **Quartz Blank:** A thin slice of synthetic quartz cut at a specific angle (usually AT-cut) to determine its resonant frequency. 2. **Electrodes:** Metallic layers (usually silver or gold) deposited on both sides of the quartz blank to apply voltage. 3. **Metal Can:** A hermetically sealed cold-weld or resistance-weld enclosure that protects the quartz from moisture and contaminants. 4. **Lead Wires:** Two conductive pins that exit through the base, used for Through-Hole Mounting (THT) on a PCB. 5. **Base/Insulator:** A glass-to-metal seal at the bottom to prevent short-circuiting between the pins and the metal casing. ### 3. Electrical Parameters When selecting or replacing an HC-49N-R, these technical specifications are critical: * **Nominal Frequency:** Measured in MHz (e.g., 8.000 MHz, 16.000 MHz). * **Load Capacitance ($C_L$):** The amount of capacitance the external circuit must provide for the crystal to oscillate at the correct frequency (often 18pF, 20pF, or 30pF). * **Frequency Tolerance:** How much the frequency deviates at room temperature (measured in PPM - parts per million). * **Frequency Stability:** How much the frequency drifts over a specific temperature range. * **Equivalent Series Resistance (ESR):** A measure of the internal resistance; lower ESR leads to easier startup of oscillation. ### 4. Common Applications * **Microcontrollers:** Providing the "heartbeat" for MCUs in embedded systems. * **Communications:** Maintaining carrier frequencies in RF modules. * **Consumer Electronics:** Used in clocks, toys, and household appliances. --- ### 5. Implementation Example In a standard Pierce Oscillator circuit (used by most microcontrollers), the HC-49N-R is connected as follows: ```c // Schematic Representation [MCU_XTAL_IN] ----+---- [HC-49N-R] ----+---- [MCU_XTAL_OUT] | | [C1] [C2] | | [GND] [GND] ``` *Note: C1 and C2 are typically ceramic capacitors chosen based on the crystal's Load Capacitance formula.*