m5stack Atomic ToUnit Base

AI context

Dense context for pasting into a model prompt — addresses, pinout, voltages, tolerances and the vendor's reference circuit.

BOARD: M5Stack Atomic ToUnit Base (A161), a 30.2 x 24.0 x 13.1 mm adapter PCB with no silicon of its own - it is two connectors and an 8-position DIP switch. It sits under an Atom-series controller and turns the Atom's bottom expansion interface into one male HY2.0-4P (Unit) socket, so a Unit-series device can be plugged into an Atom without a Grove-to-Unit cable. The switch is SW1, an SW-DIP8 8-way DIP switch, and it is the whole point of the board: it selects which Atom GPIO is routed to the Unit connector's IO1 and IO2 lines. The shipped kit is the board, a 1.5 mm hex key, one M2 x 10 mm self-tapping screw and a DIP-switch label sticker.
ADDRESSES: none. There is no I2C device, no regulator and no memory on the board - a bus scan sees only whatever a user plugs into the Unit socket.
PINOUT: 9 pads on the Atom-facing bottom interface, numbered as the vendor's own PinMap table numbers them, which puts odd pads in one column and even pads in the other. Labelled: 1 = 3V3, 3 = IO1 / IO2, 5 = IO1 / IO2, 6 = 5V, 7 = IO1 / IO2, 8 = GND, 9 = IO1 / IO2. Pads 2 and 4 carry no label in that table, so they are absent here rather than filled in - the vendor leaves them unnamed. Four pads print 'IO1 / IO2' because either line can land on any of them depending on the DIP switch, which is why the same text appears four times. The Unit-side socket is a male HY2.0-4P and is numbered 1-4 by the vendor's colour column: 1 Black GND, 2 Red 5V, 3 Yellow IO1, 4 White IO2.
SUPPLY: no regulator and no conversion. The 5V on the Unit connector's red contact comes straight from the Atom's bottom-interface 5V pad (pad 6), and the Atom itself has to be powered as it normally is over USB-C. The board adds no current limit, so the Unit is limited by the Atom's own 5 V rail.
LOGIC LEVEL: 3.3 V, unchanged. IO1 and IO2 go through the DIP switch to an Atom GPIO with no shifter and no buffer, so the Unit sees the Atom's 3.3 V logic and an Atom input sees whatever the Unit drives at 3.3 V. The only 5 V on the board is the power contact.
REFERENCE CIRCUIT: nothing to fit and nothing fitted. The schematic for A161 carries exactly four parts - J1 a 1x4P Grove-footprint socket, P1 a 4-pin header, P2 a 5-pin header and SW1 the SW-DIP8 - with no resistors and no capacitors anywhere on it, so IO1 and IO2 have no pull-ups and a Unit that needs them must bring its own. The switchable Atom pins drawn on the sheet are GPIO22, GPIO19, GPIO23 and GPIO33 for an Atom Lite, and GPIO5/6/7/8 plus GPIO39/38/21/25 for an Atom S3.
TRAPS: the switch is per-pin groups, not per-line - the vendor's instruction is that only one group may be enabled per pin and that enabling the same Atom pin on both the IO1 and the IO2 group stops the device working, so read the printed map before flipping anything. Lower switch position disables, upper enables. Because the pins the switch offers differ between Atom Lite and Atom S3, the same switch setting does not mean the same GPIO on the two boards; the sticker in the box exists for that reason. This board does not add a Grove socket or an I2C hub - it is one Unit port. It is an adapter, so it can never satisfy a land-pattern import on its own: there is no headline part to import, only the Atom it plugs into.