Mike Rankin created this tiny sensor board with an ARM Cortex M0+ microcontroller and OLED display:

It’s pretty tiny so a 4 layer board made the whole job easier. The top and bottom are pretty much dedicated for components, layer1 are tracks and power traces, layer2 is a ground plane. Mixing up an internal plane and routing layer was interesting.

The hardware consists of:

• SAMD21G18A processor (used in the Adafruit Feather)
• HDC1080DMBT temperature/humidity sensor
• ADXL345B accelerometer
• DS1340U RTC
• MCP73833 LiPo battery charger
• MicroSD card connector
• Navigation Button and pushbutton
• 0.66″ mono oled display
• Micro USB connector for charging and uploading new sketches

The design files and source code are available on GitHub:

mike-rankin/SAMD21G18A_Sensor_Board

miker has shared the board on OSH Park: