Pinout and power requirements

This reference covers the 40-pin expansion header, power rails and safe operating limits of LimerBoard N1.

The header is split into a 20-pin power/control section (J1, next to the USB port) and a 20-pin GPIO section (J2, along the outer edge). All GPIO operate at 3.3V logic.

Power pins (J1)

5V ×2 — regulated input or USB passthrough output, 1A max
3V3 ×2 — LDO output, 600mA budget for peripherals
GND ×6 — common ground

GPIO pins (J2)

GPIO1–GPIO20 support digital I/O, PWM and interrupt wake. GPIO7–GPIO10 double as I2C and SPI buses; avoid using them for general purposes if you need peripherals.

Power input options

The board accepts three input sources. It picks the highest-voltage valid source automatically — you cannot damage it by connecting USB and an external supply at once.

USB-C: 5V, up to 2A
J1 5V pin: regulated 4.8–5.25V only
Battery header (VBAT): 3.6–4.35V single-cell LiPo with onboard charger

Absolute maximum ratings

GPIO voltage: −0.3V to 3.6V (not 5V tolerant)
GPIO source/sink current: 20mA per pin, 100mA total
Operating temperature: −40°C to 85°C

Common mistakes

Feeding 5V into a GPIO — use a level shifter or divider.
Powering high-current loads (motors, heaters) from 3V3 — use an external supply.
Using GPIO7–10 for LEDs and losing the I2C bus.