There are two versions of the Weather Shield, one containing the HTU21D

and one containing the Si7021-A10. The HTU21D can be found on older

versions of the Photon Weather Shield, while the Si7021 can be found on

the latest version of the shield, V11.

The Si7021 is functionally identical to the HTU21D, and they both share the

same register addresses and command codes. To make it easier on the

user, the Photon Weather Shield library automatically detects which sensor

is present on your board without needing a separate library. More on that

later.

MPL3115A2 Barometric Pressure Sensor

The MPL3115A2 is a MEMS pressure sensor that provides Altitude data to

within 30cm. The sensor outputs are digitized by a high-resolution 24-bit

ADC and transmitted over I C. Pressure output can be resolved with output

in fractions of a Pascal, and Altitude can be resolved in fractions of a meter.

It provides 12-bit temperature measurements in degrees Celsius. This

sensor also communicates over I C and comes connected to the Photon’s

I C bus by default.

Optional Peripherals

Soil Moisture Sensor

For those who want to keep track of their houseplant conditions or for those

who want to know topsoil conditions in their gardens, the weather shield

has an optional port for a Soil Moisture Sensor.

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