veml6070: add Vishay UV light sensor

veml6070/veml6070.go

@@ -0,0 +1,140 @@
+// Package veml6070 provides a driver for the VEML6070 digital UV light sensor
+// by Vishay.
+//
+// Datasheet:
+// https://www.vishay.com/docs/84277/veml6070.pdf
+// Application Notes:
+// https://www.vishay.com/docs/84310/designingveml6070.pdf
+//
+package veml6070 // import "tinygo.org/x/drivers/veml6070"
+
+import (
+	"time"
+
+	"machine"
+)
+
+// Device wraps an I2C connection to a VEML6070 device.
+type Device struct {
+	bus         machine.I2C
+	AddressLow  uint16
+	AddressHigh uint16
+	RSET        uint32
+	IT          uint8
+}
+
+// New creates a new VEML6070 connection. The I2C bus must already be
+// configured.
+//
+// This function only creates the Device object, it does not initialize the device.
+// You must call Configure() first in order to use the device itself.
+func New(bus machine.I2C) Device {
+	return Device{
+		bus:         bus,
+		AddressLow:  ADDR_L,
+		AddressHigh: ADDR_H,
+		RSET:        RSET_240K,
+		// Note: default to maximum to get as much precision as possible since
+		// raw data values larger than 16 bit can hardly occur with RSET below
+		// 300 kOhm in real world applications. Power saving due to shorter
+		// sampling time might be a reason to reduce this.
+		IT: IT_4,
+	}
+}
+
+// Configure sets up the device for communication
+func (d *Device) Configure() bool {
+	// save power by shutdown as early as possible, also serves as presence test
+	if err := d.disable(); err != nil {
+		return false
+	}
+
+	return true
+}
+
+// ReadUVALightIntensity returns the UVA light intensity (irradiance)
+// in milli Watt per square meter (mW/(m*m))
+func (d *Device) ReadUVALightIntensity() (uint32, error) {
+	var err2 error
+
+	if err := d.enable(); err != nil {
+		return 0, err
+	}
+
+	// wait two times the refresh time to allow completion of a previous cycle
+	// with old settings (worst case)
+	time.Sleep(time.Duration(d.getRefreshTime()) * 2 * time.Millisecond)
+
+	msb, err2 := d.readData(d.AddressHigh)
+	if err2 != nil {
+		return 0, err2
+	}
+
+	lsb, err2 := d.readData(d.AddressLow)
+	if err2 != nil {
+		return 0, err2
+	}
+
+	if err := d.disable(); err != nil {
+		return 0, err
+	}
+
+	rawData := (uint32(msb) << 8) | uint32(lsb)
+
+	// normalize raw data (step count sampled in d.getRefreshTime()) into the
+	// linearly scaled normalized data (step count sampled in 100ms) for which
+	// we know the UVA sensitivity
+	normalizedData := float32(rawData) * NORMALIZED_REFRESHTIME / d.getRefreshTime()
+
+	// now we can calculate the absolute UVA power detected combining normalized
+	// data with known UVA sensitivity for this data, from datasheet
+	intensity := normalizedData * NORMALIZED_UVA_SENSITIVITY // mW/(m*m)
+
+	return uint32(intensity + 0.5), nil
+}
+
+// GetEstimatedRiskLevel returns estimated risk level from comparing UVA light
+// intensity values in mW/(m*m) with thresholds calculated from application notes
+func (d *Device) GetEstimatedRiskLevel(intensity uint32) uint8 {
+	if intensity <= 24888 {
+		return UVI_RISK_LOW
+	} else if intensity <= 49800 {
+		return UVI_RISK_MODERATE
+	} else if intensity <= 66400 {
+		return UVI_RISK_HIGH
+	} else if intensity <= 91288 {
+		return UVI_RISK_VERY_HIGH
+	} else {
+		return UVI_RISK_EXTREME
+	}
+}
+
+func (d *Device) disable() error {
+	return d.bus.Tx(uint16(d.AddressLow), []byte{CONFIG_DISABLE}, nil)
+}
+
+func (d *Device) enable() error {
+	return d.bus.Tx(uint16(d.AddressLow), []byte{CONFIG_ENABLE | d.IT}, nil)
+}
+
+func (d *Device) readData(address uint16) (byte, error) {
+	data := []byte{0}
+	err := machine.I2C0.Tx(address, []byte{}, data)
+	return data[0], err
+}
+
+// getRefreshTime returns the refresh time (aka sample time) in milliseconds
+func (d *Device) getRefreshTime() float32 {
+	var it float32
+	switch d.IT {
+	case IT_HALF:
+		it = 0.5
+	case IT_1:
+		it = 1
+	case IT_2:
+		it = 2
+	case IT_4:
+		it = 4
+	}
+	return float32(d.RSET) * RSET_TO_REFRESHTIME_SCALE * it
+}