Seeed Studio XIAO Logger HAT - Temperature, Humidity, Light & RTC

Four measurements from one tiny board: temperature, humidity, ambient light, and the exact time each reading was taken. At 21 × 17.8 mm, it stacks straight onto a XIAO, with room for a slim lithium-polymer cell sandwiched in between.

A microcontroller's internal RTC drifts badly - the designer measured roughly 10 hours of drift per year on an ESP32s clocks, against about 7 minutes per year from the on-board PCF8563 and its dedicated oscillator. That same chip draws under 1 µA and can fire a programmable interrupt to wake the host from deep sleep.

Everything sits on one I2C bus, so existing libraries work, and you can add your own sensors off the same pins. The sensors' power rail is switched by a GPIO, dropping idle draw to around 0.25 µA between samples, and a pin-enabled divider lets you read battery voltage only when you actually want it - no permanent drain on the cell.

This is a Fusion Co-Create design by Westlake University's Marcel, fully open-sourced with schematics, layout and Gerber files on GitHub, where firmware and support are maintained.

Features

• Sleeps at roughly 0.25 µA between readings, because the sensors sit on a GPIO-switched rail rather than permanent power

• Keeps usable timestamps for years - the PCF8563 RTC drifts about 7 minutes annually, and wakes the host via a programmable interrupt

• Sensirion SHT40 delivers ±0.2 °C and ±1.8 %RH accuracy with a ~2 ms read, so sampling costs almost no awake time

• BH1750 adds calibrated ambient light in lux without the guesswork of a bare photoresistor

• Track your LiPo safely through an enableable voltage divider, so battery monitoring costs nothing while idle

• Runs from 2.4–3.6 V across a -40 °C to 85 °C operating range, suitable for outdoor and cold-store deployments

• Shared I2C bus keeps the remaining XIAO pins free for your own hardware

• Open hardware: schematics, layout and Gerbers published, so you can audit or respin the design

Specifications

XIAO compatibility

The XIAO nRF54L15 series is pin-compatible but has no Arduino support yet, so software must be adapted manually.

Resources

• XIAO Logger HAT project on GitHub — firmware, updates and designer support

• Schematics (PDF)

What's included

• 1x XIAO Logger HAT board

• 2x 7-pin female header

XIAO board and lithium-polymer battery not included.