Verified 2026-10
Seeed Studio Expansion Board Base for XIAO with Grove OLED - IIC, Uart, Analog/Digital
Half-Raspberry-Pi-4-sized XIAO carrier with a 0.96 inch 128x64 I2C OLED, a PCF8563 real-time clock with CR1220 backup, a microSD slot, a passive buzzer, reset and user buttons, a 5 V servo connector, an on-board Li-ion charger and four Grove connectors (two I2C, one UART, one A0/D0); the XIAO plugs into an 18-position socket that also brings out SWD.
Place this board on a carrier in the editor →
Pinout
14 pads, as the vendor numbers them.
| # | Name | Function | Signals |
|---|---|---|---|
| 1 | D0 | A0/D0 Grove connector's signal pin | GPIO, A0, Grove A0/D0 |
| 2 | D1 | Broken out to the headers | GPIO, A1 |
| 3 | D2 | Taken by the microSD slot's chip select | GPIO, A2, SD card CS |
| 4 | D3 | Drives the passive buzzer (trace can be cut to free it) | GPIO, A3, buzzer |
| 5 | D4 | I2C data to the OLED, RTC and both I2C Grove connectors | GPIO, A4, I2C SDA |
| 6 | D5 | I2C clock to the OLED, RTC and both I2C Grove connectors | GPIO, A5, I2C SCL |
| 7 | D6 | UART transmit — Grove UART connector | GPIO, A6, UART TX |
| 8 | D7 | UART receive — Grove UART connector | GPIO, A7, UART RX |
| 9 | D8 | SPI clock to the microSD slot | GPIO, A8, SPI SCK, SD card |
| 10 | D9 | SPI data in from the microSD slot | GPIO, A9, SPI MISO, SD card |
| 11 | D10 | SPI data out to the microSD slot | GPIO, A10, SPI MOSI, SD card |
| 12 | 3V3_OUT | 3.3 V from the board's own buck converter (SYS_3V3) | 3.3 V rail |
| 13 | GND | Ground | |
| 14 | VBUS | 5 V from USB-C in; the board also feeds a 5 V boost to the servo connector |
Buses
| Bus | Signals | Pins | Voltage | Note |
|---|---|---|---|---|
| I2C ×2 | SDA, SCL | D4, D5 | 3.3 V | shared by the OLED, the RTC and both I2C Grove connectors |
| SPI ×1 | SCK, MISO, MOSI, CS | D8, D9, D10, D2 | 3.3 V | microSD slot; chip select is wired to D2, which is therefore taken while the card is in use |
| UART ×1 | TX, RX | D6, D7 | 3.3 V | Grove UART connector |
| USB ×1 | D+, D- | passed through the XIAO's USB-C; the board itself has none | ||
| SWD ×1 | SWCLK, SWDIO | on socket positions 17 and 18 (PA30 SWCLK / PA31 SWDIO); brought out to the socket's SWD pogo pads and a 2x4 header — not part of the 14-pin edge pattern |
I²C / bus addresses
| Address | Bus | Device | Note |
|---|---|---|---|
| 0x78 | I2C | 0.96 inch 128x64 OLED | as Seeed writes it in the schematic (8-bit form; 7-bit equivalent is 0x3C). Seeed notes that tying D/C# pin 15 to VCC moves it to 0x7a (7-bit 0x3D). Seeed's own example drives it with the U8x8 SSD1306 128x64 driver. |
| 0xA2 | I2C | PCF8563T real-time clock | schematic writes the pair 8-bit as T:0xA2 / R:0xA3; ±1.5 s/day at 25 C, CR1220 backup cell |
Power
| Input | USB-C 5 V through the XIAO, or a 3.7 V Li-ion on a JST 2.0 mm connector (on-board charger) |
|---|---|
| Input range | VSYS 3.6-4.5 V, VBAT 4.2 V full |
Seeed's wiki gives the charge current as 460 mA (max); the schematic block diagram says Ic 500 mA with an ETA6003 charger over a 3.7 V/1 A cell. Charging state shows on the LED as flash = no battery or not charging, on = charging, off = charged.
Outputs
| Rail | Rating | Note |
|---|---|---|
| 3V3 | 3.3 V | ETA3410 buck — system and Grove rail (SYS_3V3) |
| 5V servo | 5 V, 700 mA max | ETA1038 boost, Imax 700 mA (VBOOST_5V) |
Notes
Pin numbers 1-14 are the XIAO edge pads the socket accepts (the board has no MCU); the socket has four further positions — RST, GND and the SWD pair PA30/PA31 — which the vendor's schematic numbers 15-18 and routes to a 2x4 header and pogo pads. Not compatible with XIAO nRF54L15 or MG24 because their SWD pins differ. MicroSD is SPI with CS on D2 and shares the XIAO's SPI trio, so D2 and D8-D10 are committed while the card is used.
Provenance
Every figure on this page was read from the 3 sources below and last checked on Oct 15, 2026.