ExWindspeed

v0.1.0-beta

ExWindspeed v0.1.0-beta ExWindspeed View Source

Functions for reading data from a windspeed sensor connected through an MCP3008 analog to digital chip.

Hardware

ExWindspeed was built to support a windspeed sensor purchased from Adafruit, Anemometer Wind Speed Sensor w/Analog Voltage Output. To communicate with the device from a RaspberryPi the signal is required to be digital as there are no analog inputs on the RaspberryPi. Using a MCP3008 analog to digital chip allows communication with up to 8 channels of 10-bit analog input.

Follow the wiring section

Specifics

  • Output: 0.4V to 2V
  • Testing Range: 0.5m/s to 50m/s
  • Start wind speed: 0.2 m/s
  • Resolution: 0.1m/s
  • Accuracy: Worst case 1 m/s
  • Max Wind Speed: 70m/s

Connector details:

  • Pin 1 - Power (brown wire)
  • Pin 2 - Ground (black wire)
  • Pin 3 - Signal (blue wire)
  • Pin 4 - Not connected

The Signal wire should be connected to one of the channels described below.

Wiring

MCP3008 ADC (Analog to Digital Converter)


Channels           Connections to PI
            ____
 0        -|    |-    3.3V
 1        -|    |-    3.3V
 2        -|    |-    Ground
 3        -|    |-    Pin 18
 4        -|    |-    Pin 23
 5        -|    |-    Pin 24
 6        -|    |-    Pin 25
 7        -|____|-    Ground

Configuration

ExWindspeed supports local development by having the sensor implementation configurable. By default the Raspberry PI implementation is used and expects hardware to be connected.

SPI Device

The device to communicate with via SPI can be configured with the device key. If the device key is not configured the default SPI device will be spidev0.0.

SPI Transmission Data

Data is transmitted to the SPI device and tells the chip which channel to read from. The default bitstring will read from channel 0, if you are using another channel you can set the bitstring to use with the spi_transfer_payload key.

Local Development

If you wish to use ExWindspeed during local development the ExWindspeed.Platform.Host.SensorImpl should be used.

config :ex_windspeed, implementation: ExWindspeed.Platform.Host.SensorImpl

With the configuration shown above, all calls to ExWindspeed.read/0 shall return the same windspeed with the current UTC DateTime for read_at.

Example Configuration

The defaults are used for this example.

config :ex_windspeed,
  implementation: ExWindspeed.Platform.RPI.SensorImpl,
  device: "spidev0.0",
  spi_transfer_payload: <<0x01, 0x80, 0x00>>

Link to this section Summary

Types

meters_per_second()

Windspeed in meters per second.

miles_per_hour()

Windspeed in miles per hour.

read_at()

Date and time in UTC (using local device time) that the data was read from the sensor. If your nerves project doesn't use a means to sync local time this value will be useless.

t()

Struct containing wind speed from the sensor.

Functions

read()

Read current wind speed from sensor

Link to this section Types

Link to this type

meters_per_second() View Source 
meters_per_second() :: float()

Windspeed in meters per second.

Link to this type

miles_per_hour() View Source 
miles_per_hour() :: float()

Windspeed in miles per hour.

Link to this type

read_at() View Source 
read_at() :: DateTime.t()

Date and time in UTC (using local device time) that the data was read from the sensor. If your nerves project doesn't use a means to sync local time this value will be useless.

Link to this type

t() View Source 
t() :: %ExWindspeed{
  meters_per_second: meters_per_second(),
  miles_per_hour: miles_per_hour(),
  read_at: read_at()
}

Struct containing wind speed from the sensor.

Link to this section Functions

Link to this function

read() View Source 
read() :: {:ok, ExWindspeed.t()} | {:error, ExWindspeed.Error.t()}

Read current wind speed from sensor