Adafruit (PID 2796) Feather M0 Adalogger Measures 2.0" x 0.9" x 0.28" (51mm x 23mm x 8mm) without headers soldered in Light as a (large?) feather - 5.3 grams. 32.768 KHz crystal for clock generation & RTC ATSAMD21G18 @ 48MHz with 3.3V logic/power 256KB of FLASH + 32KB of RAM No EEPROM. You also get tons of pins - 20 GPIO pins Hardware Serial, hardware I2C, hardware SPI support PWM outputs on all pins 6 x 12-bit analog inputs 1 x 10-bit analog ouput (DAC) 3.3V regulator with 500mA peak current output. Built in 100mA lipoly charger with charging status indicator LED USB native support, comes with USB bootloader and serial port debugging