Support for ADT7410 temperature sensor (#109)

* ADT7410: add support for i2c temperature sensor

adt7410/adt7410.go

@@ -0,0 +1,90 @@
+package adt7410
+
+import (
+	"machine"
+	"time"
+)
+
+type Error uint8
+
+const (
+	ErrInvalidID Error = 0x1
+)
+
+func (e Error) Error() string {
+	switch e {
+	case ErrInvalidID:
+		return "Invalid chip ID"
+	default:
+		return "Unknown error"
+	}
+}
+
+type Device struct {
+	bus  *machine.I2C
+	buf  []byte
+	addr uint8
+}
+
+// New returns ADT7410 device for the provided I2C bus and address. The ADT7410
+// has a default address of 0x48 (1001000).  The last 2 bits of the address
+// can be set using by connecting to the A1 and A0 pins to VDD or GND (for a
+// total of up to 4 devices on a I2C bus).  Also note that 10k pullups are
+// recommended for the SDA and SCL lines.
+func New(i2c *machine.I2C, addressBits uint8) *Device {
+	return &Device{
+		bus:  i2c,
+		buf:  make([]byte, 2),
+		addr: Address | (addressBits & 0x3),
+	}
+}
+
+func (dev *Device) Configure() (err error) {
+
+	// verify the chip ID
+	// TODO: According to datasheet, the check below should work; however
+	//       this does not seem to be working right, but is not exactly
+	//       necessary, so can revisit later to see if there is a bug
+	//id := dev.ReadByte(RegID) & 0xF8
+	//if id != 0xC8 {
+	//	err = ErrInvalidID
+	//}
+
+	// reset the chip
+	dev.writeByte(RegReset, 0xFF)
+	time.Sleep(10 * time.Millisecond)
+	return
+
+}
+
+// ReadTemperature returns the temperature in celsius milli degrees (ºC/1000)
+func (d *Device) ReadTemperature() (temperature int32, err error) {
+	return (int32(d.readUint16(RegTempValueMSB)) * 1000) / 128, nil
+}
+
+// ReadTempC returns the value in the temperature value register, in Celcius
+func (d *Device) ReadTempC() float32 {
+	t := d.readUint16(RegTempValueMSB)
+	return float32(int(t)) / 128.0
+}
+
+// ReadTempF returns the value in the temperature value register, in Fahrenheit
+func (d *Device) ReadTempF() float32 {
+	return d.ReadTempC()*1.8 + 32.0
+}
+
+func (d *Device) writeByte(reg uint8, data byte) {
+	d.buf[0] = reg
+	d.buf[1] = data
+	d.bus.Tx(uint16(d.addr), d.buf, nil)
+}
+
+func (d *Device) readByte(reg uint8) byte {
+	d.bus.ReadRegister(d.addr, reg, d.buf)
+	return d.buf[0]
+}
+
+func (d *Device) readUint16(reg uint8) uint16 {
+	d.bus.ReadRegister(d.addr, reg, d.buf)
+	return uint16(d.buf[0])<<8 | uint16(d.buf[1])
+}

adt7410/registers.go

@@ -0,0 +1,24 @@
+package adt7410
+
+const (
+	// Default I2C address
+	Address = 0x48
+
+	// Temperature Value MSB Register
+	RegTempValueMSB = 0x0
+
+	// Temperature Value LSB Register
+	RegTempValueLSB = 0x1
+
+	// Status Register
+	RegStatus = 0x2
+
+	// Config Register
+	RegConfig = 0x3
+
+	// ID Register
+	RegID = 0x0B
+
+	// Software Reset Register
+	RegReset = 0x2F
+)