Feather Standard Pinout Extension & Spec Interpretation

[0Grit]

See #3 for initial context of this discussion

The Feather pin spec leaves a lot to be desired for professional use cases. (As expected) But it seems to be used often so lets see if we can improve upon it in a backwards compatible way.

Feather Spec is here: https://learn.adafruit.com/adafruit-feather/feather-specification
The spec does not do much to constrain potential interpretations. I will leave comments for my own interpretations in order to enable them to be discussed individually.

Below I have created a table that shows the pinout and have summarily described the pin functions. I'd like the outcome of the discussion to be

• How to involve Adafruit if desired
• Which pins to add
• Where to add them
• Ensure the additions will be backward compatible

Left Header	Function	⬛	Right Header	Function
Rst	Active low; "main feather board reset line"	⬛	No Pin
3.3V	3.3V pin powers wings. Take VUSB/VBAT to 3.3V	⬛	No Pin
Aref	Analog reference, usually for the host processor	⬛	No Pin
GND	This is the COMMON reference point	⬛	No Pin
A0	Analog 0	⬛	Bat	LiPoly battery voltage (3.0-3.7V) (Battery being present should result in VUSB being disconnected
A1	Analog 1	⬛	En	Input to mainboard; must depower the 3.3V output. PLEASE CONNECT THIS TO A GPIO OF THE HOST PROCESSOR AS WELL
A2	Analog 2	⬛	USB	?!?!? Spec refers to three different nets that could actually be the same thing (USB, VBUS, VUSB)
A3	Analog 3	⬛	D13	Digital IO (User LED)
A4/D24	Analog 4 (D24 DIGITAL IO ONLY IF NO ANALOG AVAILABLE)	⬛	D12	Digital IO
A5/D25	Analog 5 (D25 DIGITAL IO ONLY IF NO ANALOG AVAILABLE)	⬛	D11	Digital IO
SCK	Serial CLock (SPI)	⬛	D10	Digital IO
MO	Manager out, Subordinate In (SPI)	⬛	D9	Digital IO
MI	Manager In, Subordinate out (SPI)	⬛	D6	Digital IO
RX/D0	I will assume this is application RX (Not Debug RX)	⬛	D5	Digital IO
TX/D1	I will assume this is application TX (Not Debug TX)	⬛	SCL	Serial Clock Line (I2C) (They recommend having the wings pull on the i2c lines)
⭐	"Free Pin", more like "zombie pin" This may as well be DNP.	⬛	SDA	Serial Data line (I2C) (They recommend having the wings pull in the i2c lines)

[0Grit]

@pedrominatel when I originally was drafting this discussion I had a good half hour's worth of comments that github lost when I realized I hadn't selected a category yet and selected one. (Now a known discussions bug)

Is it too late for me to capture those notes/comments here?

[MabezDev]

@0Grit Sorry to hear your comments got lost, we would definitely appreciate your input! It's definitely not too late :)

If you'd like to talk about the board myself and pedro will be in the community meeting which you are welcome to join.

[pedrominatel]

Hi @0Grit, I've used this proposal as a starting point for the proposal at Pin Layout.

Feel free to let your comments there, or prepare a PR.

Thanks!