A very small narrow-DIP-sized, Arduino Zero compatible USB dev board (OTG enabled), with integrated buck and boost power supplies!

Version with headers already soldered

Specifications

• CPU: 32-bit Cortex M0+ ATSAMD21-series running at 48 MHz (Arduino Zero Compatible)
• FLASH: 256 kB (248 kB due to integrated bootloader).
• RAM: 32 kB, zero wait states.
• Powered via USB or externally (3.3V to 5V).
• Integrated 500-mA boost and 1-A buck converters and automatic power switching circuitry. 
• Each converter can also be individually turned off, e.g. if you want to force power draw exclusively from external pins (self-powered device), or if you want to turn off an external USB device connected with a micro A cable.
• When powered through the USB port, the output voltage on the power pins can be selected via software to be either 3.3V or the USB voltage (typically 5V +/- 10%).
• Pin 15 can be configured (via SMD jumper) as an additional 3.3V auxiliary output @100mA when pin 16 is 5V (either as input or output). By default pin 15 is a regular I/O. If this feature is not used, 5/3.3V (at up to 1A) are still available on pin 16.
• 14 I/O pins (2 of them can be used to connect an external SWD programmer/debugger) and 2 power pins (VCC and GND).
• Status LED (it can be turned on/off via software using a single instruction).
• Multi function push button for reset/program.
• 8 12-bit ADC inputs.
• 10-bit DAC output.
• 14 external interrupt input pins.
• Up to 5 serials between SPI, I2C, UART and I2S.
• I2S port for audio decoders such as  UDA1334A.
• 13 PWM pins.
• Size: 28.5 mm x 10.16 mm (1.1 “ x 0.40 “), including USB port protrusions (27.23 mm x 10.16 mm excluding USB)
• 4-layer board for improved noise performance.
• Standards narrow-DIP footprint: 0.3” (7.62 mm) row spacing, 0.1” (2.54) pin spacing.
• Pinout standard logic CMOS compatible: power and GND are on pin 16 and 8, so you can also emulate some 16 pin CMOS ICs (4000 and 74HC series)! 
• Can be programmed in C/C++, asm, and also CircuitPython!