From 92050d90da50fd2b9007eaca52909df36fd2904b Mon Sep 17 00:00:00 2001 From: Ayke van Laethem Date: Fri, 17 Nov 2023 20:50:53 +0100 Subject: [PATCH] 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 | 53 +++++++++++++ sgp30/sgp30.go | 169 +++++++++++++++++++++++++++++++++++++++++ smoketest.sh | 1 + 3 files changed, 223 insertions(+) create mode 100644 examples/sgp30/main.go create mode 100644 sgp30/sgp30.go diff --git a/examples/sgp30/main.go b/examples/sgp30/main.go new file mode 100644 index 0000000..bf586b6 --- /dev/null +++ b/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()) + } +} diff --git a/sgp30/sgp30.go b/sgp30/sgp30.go new file mode 100644 index 0000000..4443de7 --- /dev/null +++ b/sgp30/sgp30.go @@ -0,0 +1,169 @@ +// SGP30 VOC sensor. +// +// This sensor is marked obsolete by Sensirion, but is still commonly available. +// +// Datasheet: https://sensirion.com/media/documents/984E0DD5/61644B8B/Sensirion_Gas_Sensors_Datasheet_SGP30.pdf +package sgp30 + +import ( + "errors" + "time" + + "tinygo.org/x/drivers" +) + +const Address = 0x58 + +var ( + errInvalidCRC = errors.New("sgp30: invalid CRC") +) + +type Device struct { + bus drivers.I2C + commandBuf [2]byte + responseBuf [9]byte + readyTime time.Time + co2eq uint16 + tvoc uint16 +} + +type Config struct { + // Nothing to configure right now. +} + +// New returns a new SGP30 driver instance. It does not touch the device yet, +// call Configure to configure this sensor. +func New(bus drivers.I2C) *Device { + return &Device{ + bus: bus, + // The sensor has a maximum powerup time of 0.6ms. + // See table 6 in the datasheet. + readyTime: time.Now().Add(600 * time.Microsecond), + } +} + +// Connected returns whether something (probably a SGP30) is present on the bus. +func (d *Device) Connected() bool { + d.waitUntilReady() + + // Request serial ID. + d.commandBuf = [2]byte{0x36, 0x82} + err := d.bus.Tx(Address, d.commandBuf[:], nil) + if err != nil { + return false + } + + // Wait 0.5ms as specified in the datasheet. + time.Sleep(500 * time.Microsecond) + + // Read the serial ID from the sensor. + err = d.bus.Tx(Address, nil, d.responseBuf[:9]) + if err != nil { + return false + } + + // Check whether the CRC matches. + _, ok1 := readWord(d.responseBuf[:3]) + _, ok2 := readWord(d.responseBuf[3:6]) + _, ok3 := readWord(d.responseBuf[6:9]) + ok := ok1 && ok2 && ok3 + + return ok +} + +// Wait until a previous command has completed. This may be necessary on +// startup, for example. +func (d *Device) waitUntilReady() { + now := time.Now() + delay := d.readyTime.Sub(now) + if delay > 0 { + time.Sleep(delay) + } +} + +// Configure starts the measurement process for the SGP30 sensor. +func (d *Device) Configure(config Config) error { + d.waitUntilReady() + + // Send the sgp30_iaq_init command. + d.commandBuf = [2]byte{0x20, 0x03} + err := d.bus.Tx(Address, d.commandBuf[:], nil) + + // The next command will have to wait at least 10ms. + d.readyTime = time.Now().Add(10 * time.Millisecond) + + return err +} + +// Read the current CO₂eq and TVOC values from the sensor. +// This method must be called around once per second per the datasheet as this +// is how the sensor algorithm was calibrated. +func (d *Device) Update(which drivers.Measurement) error { + d.waitUntilReady() + + // Send sgp30_measure_iaq command. + d.commandBuf = [2]byte{0x20, 0x08} + err := d.bus.Tx(Address, d.commandBuf[:], nil) + if err != nil { + return err + } + + // Wait until the response is ready. + // This can take up to 12ms according to the datasheet. + time.Sleep(12 * time.Millisecond) + + // Read the response. + data := d.responseBuf[:6] + err = d.bus.Tx(Address, nil, data) + if err != nil { + return err + } + + // Decode the response. + co2eq, ok1 := readWord(data[0:3]) + tvoc, ok2 := readWord(data[3:6]) + if !ok1 || !ok2 { + return errInvalidCRC + } + d.co2eq = co2eq + d.tvoc = tvoc + + return nil +} + +// Returns the CO₂ equivalent value read in the previous measurement. +// +// Warning: this is _not_ an actual CO₂ value. The SGP30 can't actually read +// CO₂. Instead, it's an approximation based on various other gases in the +// environment. +func (d *Device) CO2() uint32 { + return uint32(d.co2eq) +} + +// Returns the total number of VOCs (volatile organic compounds) in parts per +// billion (ppb). +func (d *Device) TVOC() uint32 { + return uint32(d.tvoc) +} + +// Read a single 16-bit word from the sensor and check the CRC. The data +// parameter must be a slice of 3 bytes. +func readWord(data []byte) (value uint16, ok bool) { + if len(data) != 3 { + return 0, false + } + value = uint16(data[0])<<8 | uint16(data[1]) + crc := uint8(0xff) + for i := 0; i < 2; i++ { + crc ^= data[i] + for b := 0; b < 8; b++ { + if crc&0x80 != 0 { + crc = (crc << 1) ^ 0x31 + } else { + crc <<= 1 + } + } + } + ok = crc == data[2] + return +} diff --git a/smoketest.sh b/smoketest.sh index 777401e..b29dd7a 100755 --- a/smoketest.sh +++ b/smoketest.sh @@ -62,6 +62,7 @@ tinygo build -size short -o ./build/test.hex -target=pico ./examples/pca9685/mai tinygo build -size short -o ./build/test.hex -target=microbit ./examples/pcd8544/setbuffer/main.go tinygo build -size short -o ./build/test.hex -target=microbit ./examples/pcd8544/setpixel/main.go tinygo build -size short -o ./build/test.hex -target=arduino ./examples/servo +tinygo build -size short -o ./build/test.hex -target=pico ./examples/sgp30 tinygo build -size short -o ./build/test.hex -target=pybadge ./examples/shifter/main.go tinygo build -size short -o ./build/test.hex -target=microbit ./examples/sht3x/main.go tinygo build -size short -o ./build/test.hex -target=microbit ./examples/sht4x/main.go