12MHz Crystal with 18pF Caps

12MHz Crystal Oscillator with 18pF Load Capacitors — Arduino & ATmega Microcontroller Clock

A 12MHz fundamental mode quartz crystal resonator in HC-49S (or HC-49US low-profile) package, supplied with a matched pair of 18pF ceramic load capacitors for a complete crystal oscillator circuit. The 12MHz crystal is commonly used as the clock source for ATmega microcontrollers (ATmega328P, ATmega2560, ATmega32U4) in standalone Arduino circuits, USB interface circuits (where 12MHz provides the exact USB full-speed clock), and general-purpose microcontroller clock applications. The 18pF load capacitors are matched to the crystal’s specified load capacitance for accurate frequency operation.

Technical Specifications

Parameter	Value
Frequency	12.000MHz
Frequency Tolerance	±30ppm (at 25°C)
Frequency Stability	±50ppm (−20°C to +70°C)
Load Capacitance	18pF (matched capacitors included)
Package	HC-49S (through-hole, 2-pin)
Equivalent Series Resistance (ESR)	<80Ω
Drive Level	100µW max
Operating Temperature	−20°C to +70°C
Certification	RoHS

Why 12MHz for USB Applications?

USB Speed	Bit Rate	Required Clock	12MHz Suitability
USB Low Speed	1.5Mbps	12MHz / 8 = 1.5MHz	Yes (exact)
USB Full Speed	12Mbps	12MHz (exact)	Yes (exact)
USB High Speed	480Mbps	480MHz	No (requires PLL)

Crystal Oscillator Circuit

Connect the crystal and load capacitors as follows for ATmega microcontrollers:

• Crystal pin 1 → XTAL1 pin of ATmega + 18pF capacitor to GND
• Crystal pin 2 → XTAL2 pin of ATmega + 18pF capacitor to GND
• Set ATmega fuse bits to external crystal oscillator mode (CKSEL = 1111, SUT = 11 for 12MHz crystal)

Typical Applications

• Standalone Arduino: 12MHz clock source for standalone ATmega328P Arduino circuits on custom PCBs
• USB Interface: 12MHz crystal for ATmega32U4 and V-USB software USB implementations requiring exact 12MHz clock
• Microcontroller Clock: General-purpose 12MHz clock source for PIC, AVR, STM32, and other microcontrollers supporting external crystal oscillators
• UART Baud Rate: 12MHz provides exact baud rates for 9600, 19200, 38400, 57600, and 115200 bps UART communication with zero error

FAQ

Q: Can I use a 12MHz crystal instead of the standard 16MHz Arduino crystal?
A: Yes. ATmega328P supports 12MHz external crystal. Update the Arduino board definition to 12MHz (or use a custom boards.txt entry) to ensure correct timing for delay(), millis(), and UART baud rate calculations.

Q: Why are 18pF capacitors included?
A: The 18pF load capacitors are required for the crystal oscillator circuit to oscillate at the specified frequency. The capacitor value must match the crystal’s specified load capacitance (CL = 18pF for this crystal). Using incorrect capacitor values will cause frequency error or oscillation failure.

Package Contents

• 1 × 12MHz HC-49S quartz crystal
• 2 × 18pF ceramic capacitors (load capacitors)

Enjoy free standard shipping on all orders over $199 USD. Orders are processed within 1–2 business days.

Not satisfied? Return any item within 90 days of purchase for a full refund or exchange. Items must be in original condition.

We are committed to quality, reliability, and customer satisfaction. Every product is carefully selected and tested to meet the highest standards.