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112 lines
2.7 KiB
Go
112 lines
2.7 KiB
Go
package i2c
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import (
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"bytes"
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"encoding/binary"
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)
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const bme280RegisterHumidityMSB = 0xFD
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const bme280RegisterCalibDigH1 = 0xa1
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const bme280RegisterCalibDigH2LSB = 0xe1
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type humidityCalibrationCoefficients struct {
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h1 uint8
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h2 int16
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h3 uint8
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h4 int16
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h5 int16
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h6 int8
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}
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// BME280Driver is a driver for the BME280 temperature/humidity sensor
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type BME280Driver struct {
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*BMP180Driver
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hc *humidityCalibrationCoefficients
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}
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// NewBME280Driver creates a new driver with specified i2c interface.
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// Params:
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// conn Connector - the Adaptor to use with this Driver
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//
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// Optional params:
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// i2c.WithBus(int): bus to use with this driver
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// i2c.WithAddress(int): address to use with this driver
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//
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func NewBME280Driver(a Connector, options ...func(Config)) *BME280Driver {
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b := &BME280Driver{
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BMP180Driver: NewBMP180Driver(a),
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hc: &humidityCalibrationCoefficients{},
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}
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for _, option := range options {
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option(b)
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}
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return b
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}
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// Start initializes the BME280 and loads the calibration coefficients.
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func (d *BME280Driver) Start() (err error) {
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bus := d.GetBusOrDefault(d.connector.GetDefaultBus())
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address := d.GetAddressOrDefault(bmp180Address)
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if d.connection, err = d.connector.GetConnection(address, bus); err != nil {
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return err
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}
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if err := d.initialization(); err != nil {
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return err
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}
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if err := d.initHumidity(); err != nil {
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return err
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}
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return nil
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}
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// read the humidity calibration coefficients.
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func (d *BME280Driver) initHumidity() (err error) {
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var coefficients []byte
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if coefficients, err = d.read(bme280RegisterCalibDigH1, 1); err != nil {
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return err
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}
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buf := bytes.NewBuffer(coefficients)
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binary.Read(buf, binary.BigEndian, &d.hc.h1)
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if coefficients, err = d.read(bme280RegisterCalibDigH2LSB, 7); err != nil {
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return err
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}
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buf = bytes.NewBuffer(coefficients)
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binary.Read(buf, binary.LittleEndian, &d.hc.h2)
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binary.Read(buf, binary.BigEndian, &d.hc.h3)
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binary.Read(buf, binary.BigEndian, &d.hc.h4)
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binary.Read(buf, binary.BigEndian, &d.hc.h5)
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binary.Read(buf, binary.BigEndian, &d.hc.h6)
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return nil
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}
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// Humidity returns the current humidity in percentage of relative humidity
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func (d *BME280Driver) Humidity() (humidity float32, err error) {
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var rawH int16
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if rawH, err = d.rawHumidity(); err != nil {
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return 0, nil
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}
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//TODO: return d.calculateHumidity(rawH), nil
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return float32(rawH / 1024.0), nil
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}
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func (d *BME280Driver) rawHumidity() (int16, error) {
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ret, err := d.read(bme280RegisterHumidityMSB, 2)
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if err != nil {
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return 0, err
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}
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buf := bytes.NewBuffer(ret)
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var rawH int16
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binary.Read(buf, binary.BigEndian, &rawH)
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return rawH, nil
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}
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func (d *BME280Driver) calculateHumidity(rawH int16) float32 {
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// TODO: real adjustment based on hc coefficients
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return 0.0 / 1024.0
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}
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