We put a ton of stuff on this HalloWing, above you can see a 'guided tour' of whats available!

Power Pins & Ports

There's two ways to power your Hallowing. The best way is to plug in a 3.7/4.2V Lipoly battery into the JST 2-PH port. You can then recharge the battery over the Micro USB jack. You can also just run the board directly from Micro USB, it will automatically 'switch over' to USB power when that's plugged in

The Hallowing JST battery port is expecting a LiPo with the 'standard' Adafruit polarity wiring. Using other battery packs with opposite wiring or voltages may destroy your Hallowing!
Slim Lithium Ion Polymer Battery 3.7v 400mAh with JST 2-PH connector and short cable
Lithium-ion polymer (also known as 'lipo' or 'lipoly') batteries are thin, light, and powerful. The output ranges from 4.2V when completely charged to 3.7V. This...

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)

Chip & Flash

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!


There's a few built in sensors.


On the top there's a light sensor, connected to pin A1 - it's reverse mount so you can read light levels from the front.


There's also a LIS3DH 3-axis accelerometer connected to the I2C pins for detection motion, tilt or taps

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


There are three LEDs - a red LED on pin D13, a CHG LED that will let you know when the battery is charging, and a NeoPixel on D8 (in Arduino) or board.NEOPIXEL (in CircuitPython)


It's normal for the yellow CHG LED to flicker when no battery is in place, that's the charge circuitry trying to detect whether a battery is there or not. If you are powering only over USB, you can cover it with tape

The charge LED is automatically driven by the Lipoly charger circuit. It will try to detect a battery and is expecting one to be attached. If there isn't one it may flicker once in a while when you use power because it's trying to charge a (non-existant) battery. It's not harmful, and its totally normal!


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.

This guide was first published on Aug 15, 2018. It was last updated on Feb 14, 2024.

This page (Pinouts) was last updated on Aug 15, 2018.

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