We put a ton of stuff on this HalloWing, above you can see a 'guided tour' of whats available!
You can turn off power completely with the on/off switch at the bottom of the board.
If you need access to the power pins, the 'Feather Headers' have 3.3V regulated out, GND (labeled G) on the left. On the right there's the BAT pin (connects directly to lipoly) and two pins below that is the USB pin. You can measure the voltage on the battery by reading analog pin A6 - this is divided by two with resistors so don't forget to x2 once you do the reading. The voltage, after doubling, will range from about 3.5 (empty) to 4.2V (charged)
The main processor chip is the ATSAMD21G18 Cortex M0+ running at 48MHz with 3.3V logic/power. It has 256KB of FLASH + 32KB of RAM and can run Arduino or CircuitPython
We also include 8 MB of SPI Flash for storing images, sounds, animations, whatever!
On the bottom of the board are four pads designed for capacitive touch. They are connected to A2, A3, A4 and A5
On the right is a SENSE port, this is a JST 3-PH for connecting an external sensor. From the top to bottom the pads are GND, V+, D3 (in Arduino this is also A11). V+ is either LiPoly or USB power, whchever is plugged in and higher. There's a 470 ohm+3.6V zener diode connection to protect against voltages higher than 3.3V coming in.
We have a mono 2 Watt class D audio amp connected to A0 - that's the DAC output on the SAMD21, so you can get 10-bit audio output, good for many simple sound effects or musical output. There's a small smt trimpot you can adjust if you want, but the default 50% setting is pretty good.
The connector for the speaker is a Molex PicoBlade, but there's large pads you can solder too if you want to connect a custom speaker
On the front is a 128x128 TFT. The TFT is connected to the SPI pins: SCK and MOSI (MISO is not connected)
We also use pin #37 for TFT Reset, #38 for TFT DC, #39 for TFT CS, and #7 for the backlight which is default-off.