sgp30: add the now-obsolete SGP30 air quality sensor

Tested with a rp2040.

TODO: add the ability to set the absolute humidity for more accurate
sensor details. The formula for that is rather complex, so I've left
this as a future addition.

examples/sgp30/main.go

@@ -0,0 +1,53 @@
+package main
+
+// Example for the SGP30 to be used on a Raspberry Pi pico.
+// Connect the sensor I2C pins to GP26 and GP27 to test.
+
+import (
+	"machine"
+	"time"
+
+	"tinygo.org/x/drivers/sgp30"
+)
+
+func main() {
+	time.Sleep(time.Second)
+	println("start")
+
+	// Configure the I2C bus.
+	bus := machine.I2C1
+	err := bus.Configure(machine.I2CConfig{
+		SDA:       machine.GP26,
+		SCL:       machine.GP27,
+		Frequency: 400 * machine.KHz,
+	})
+	if err != nil {
+		println("could not configure I2C:", bus)
+		return
+	}
+
+	// Configure the sensor.
+	sensor := sgp30.New(bus)
+	if !sensor.Connected() {
+		println("sensor not connected")
+		return
+	}
+	err = sensor.Configure(sgp30.Config{})
+	if err != nil {
+		println("sensor could not be configured:", err.Error())
+		return
+	}
+
+	// Measure every second, as recommended by the datasheet.
+	for {
+		time.Sleep(time.Second)
+
+		err := sensor.Update(0)
+		if err != nil {
+			println("could not read sensor:", err.Error())
+			continue
+		}
+		println("CO₂ equivalent:", sensor.CO2())
+		println("TVOC           ", sensor.TVOC())
+	}
+}