Why did you make it?

After making a breakout for the MCP39F511 I wanted to try out its sibling ASIC the 521. The difference between these is essentially the serial interface. The 511 uses an UART while the 521 uses i2c. UART's are more common and present on most microcontrollers or embedded systems, but are fewer in number, while i2c ports are rarer but a single i2c port can serve multiple of these ASICs allowing monitoring of upto 4 circuits or 32 using an i2c expander such as TCA9548A. Without i2c we would be hard pressed to build a 32 channel energy measurement device with a single higher level microcontroller.

What makes it special?

This breakout is no-frills and provides a cost-effective development tool for firmware engineers to get started with integrating this ASIC on their end devices. It also allows experimenting with confidence without using high voltages the manufacturer kits or even the excellent integrated solution from Upbeatlabs Drwattson requires.