What this product does Breakout board for Adafruit’s Si5351A clock generator. Uses an internal, accurate 25 MHz crystal reference to drive the chip’s PLLs and frequency dividers so you can generate virtually any clock frequency under program control. Key benefits — why you need it Replace fixed crystals: program precise output frequencies instead of committing to single-purpose crystals. Flexible multi-output clocking: three independent outputs let you run multiple subsystems at different frequencies from one chip. Easy integration: I2C control and on-board level shifting let you use the board with 3.3V or 5V microcontrollers without extra circuitry. Simple power requirements: built-in 3.3V LDO regulator lets the board run from a 3–5 VDC supply. Important features and specifications Si5351A clock generator chip (Adafruit breakout). Internal, accurate 25 MHz crystal reference. I2C-controlled PLLs and clock dividers — set PLL and divider values via I2C instructions to produce precise frequencies. Three independent outputs; each output can be configured to a different frequency. Output level described as 3 Vss, available on a breadboard-friendly connector or an optional SMA connector. Breakout board includes a 3.3V LDO regulator; operating voltage 3–5 VDC. I2C lines include a level-shift circuit to support both 3V and 5V logic safely. Compatibility and performance Controlled over I2C, compatible with most microcontrollers and single-board computers that provide I2C. Designed for breadboard and prototyping use via standard connector; SMA option available for lab and RF connections. Precise frequency generation is achieved by configuring the chip’s PLLs and dividers using the internal 25 MHz reference. Typical applications Prototype development: provide multiple, independent clocks for microcontrollers, FPGAs, or digital logic on a development bench without swapping crystals. Test and measurement: generate reference clocks or signal sources for lab experiments and equipment calibration. RF and hobby projects: supply different clock frequencies to radio modules, synthesizers, and timing-sensitive circuits with a compact board and optional SMA connection. Practical notes Configure frequencies by writing PLL and divider settings over I2C; the internal crystal is used as the reference for accurate, stable outputs. Power the board with a 3–5 VDC supply; the onboard 3.3V regulator and I2C level-shifter make it safe to interface with both 3V and 5V logic. Use the breadboard-friendly connector for quick prototyping; use the SMA connector when a coaxial connection or better signal integrity is required. This Si5351A breakout provides a compact, flexible, and accurate solution for multi-output clock generation controlled via I2C, suitable for development, testing, and hobby projects where programmable, independent clock outputs are needed.