Common Pin Allocations

This table describe common uses for the Feather M0 pins by Loom and the OPEnS Lab.

See the Adafruit pinout diagram for more details of the pinouts.

Pin	Use	Boards	Notes
4	SD chip select	Feather M0 Adalogger	Unlike the Adalogger Featherwing and Hypnos, which use pin 10 for SD CS, this board uses pin 4
5	3.3V Rail control	Hypnos	LOW for close circuit (conduct / active), otherwise, the pin is pulled HIGH for open circuit (not conduct / disabled).
6	5V Rail control	Hypnos	HIGH for close circuit (conduct / active), the PIN is pulled LOW for open circuit (disabled)
9	GPIO	Feather M0	Adafruit: "Also analog input A7. This analog input is connected to a voltage divider for the lipoly battery so be aware that this pin naturally 'sits' at around 2VDC due to the resistor divider." If you use this pin for digital IO, you may get incorrect battery voltage readings. There are some additional issues, such as not being able to toggle a latching relay on this pin.
10	SD chip select	Adalogger Featherwing	Can be changed by jumping to other pin
11	SD chip select	Hypnos	Can be changed by jumping to other pin
12	Interrupt	Hypnos	The digital input for the interrupt signal from the DS3231 on the Hypnos board. For consistency, we often use pin 12 as the interrupt pin even when not using Hypnos, such as using the DS3231 featherwing or PCF8523 feather
13	Builtin LED	Feather M0	Can be used as a digital pin, but will impact LED behavior

Note: Hypnos is the OPEnS Lab's general purpose deployment board, featuring SD, RTC, and low power features. Details can be found on the OPEnS Lab Wiki here.