Adafruit Circuit Playground Express
-M0+ core. The SAM L21 features sophisticated power management technologies, allowing for very low current consumption. It can be powered by USB, "AAA" battery pack, or with a Lipoly battery. The round, sensor-packed Circuit Playground Express Board features alligator-clip pads around the edge, making it easy to connect to projects without having to solder. Built-in USB allows quick connectivity for programming, with no special cables or adapters required.