While the layout of the board is designed to stack with a Moteino, there are only a few required pins to use the WeatherShield. In fact you could get by with only 4 pins if you wanted to use the board with another type of arduino: GND, 3.3v, SCL and SDA.

Note that the BME280 sensor will require 1.71-3.6V (supplied via the 3v3 pin), anything more will damage the sensor!

The BME280 sensor is wired to use the default I2C interface with the default 0x77 address.

Battery/VIN monitor

The VIN pin is used in a voltage divider that is then fed to A7 on the Moteino, which can then read this value and estimate the battery or VIN voltage.

This divider has a ratio of 2/3 of the actual VIN and is required because the VIN is greater than the 3.3V operating voltage of the Moteino. This means a readable VIN range through this monitor is up to about 5V before A7 saturates to the max reading of 1023 (10bit ADC on the ATMega328p), hence the recommended voltage on VIN should be around 5V.

Disabling the VIN monitor

The monitor is permanently wired to VIN and at 5V will drain about 1.6uA. This is a very small amount of current and the previous revision included a mosfet to disable the monitor when not in use, in fact the pads are still there to support it but a jumper was placed instead to permanently enable it (the angled resistor). If you do not want to use this monitor and need to save that extra tiny amount of current you can do so by cutting the trace below, or if you’re brave enough, you may desolder the angled resistor and solder a SOT23-3 P-mosfet which has its gate wired to A3.

I2C interface

Note that SCL and SDA are pulled up with 4.7K resistors. The left side of the board has SMD jumpers which you can break to disable these resistors or use different values, but the default values should always work. If you have other I2C

BME280 Specifications

For more detailed specifications see the manufacturer BME280 datasheet.

Also check out this extensive comparison between BME280 and many other temperature/humidity sensors, the conclusion being that the BME280 is the clear winner among the tested devices.