Add basic support for INA219 current sensor

sensor/ina219/ina219.go

@@ -0,0 +1,131 @@
+// Package ina219 allows interfacing with Texas Instruments INA219 current
+// monitor. This is a high side current and voltage monitor with and I2C
+// interfcace.
+
+// TODO - add options to config voltage range, sensitivity and averaging
+
+package ina219
+
+import (
+	"math"
+	"sync"
+
+	"github.com/golang/glog"
+	"github.com/kidoman/embd"
+)
+
+const (
+	configReg  = 0x00
+	shuntVReg  = 0x01
+	busVReg    = 0x02
+	powerReg   = 0x03
+	currentReg = 0x04
+	calibReg   = 0x05
+)
+
+// INA219 represents a Bosch INA219 current sensor.
+type INA219 struct {
+	Bus embd.I2CBus
+
+	address        byte
+	shuntResitance float64
+
+	initialized bool
+	mu          sync.RWMutex
+}
+
+func New(bus embd.I2CBus, addr byte, shunt float64) *INA219 {
+	ina := INA219{
+		Bus:            bus,
+		address:        addr,
+		shuntResitance: shunt,
+	}
+	return &ina
+}
+
+func (d *INA219) setup() error {
+	d.mu.RLock()
+	if d.initialized {
+		d.mu.RUnlock()
+		return nil
+	}
+	d.mu.RUnlock()
+
+	d.mu.Lock()
+	defer d.mu.Unlock()
+
+	config := uint16(0x219F) // 12, bit no integration, 32v bus range , 40mV shunt range
+	err := d.Bus.WriteWordToReg(d.address, configReg, config)
+	if err != nil {
+		return err
+	}
+
+	calib := uint16(0.5 + 40.96/d.shuntResitance)
+
+	err = d.Bus.WriteWordToReg(d.address, calibReg, calib) // .1 ohm sense resitor
+	if err != nil {
+		return err
+	}
+
+	glog.V(1).Infof("ina219: initaliized")
+
+	d.initialized = true
+
+	return nil
+}
+
+func (d *INA219) ShuntVoltage() (float64, error) {
+	if err := d.setup(); err != nil {
+		return math.NaN(), err
+	}
+
+	v, err := d.Bus.ReadWordFromReg(d.address, shuntVReg)
+	if err != nil {
+		return math.NaN(), err
+	}
+
+	voltage := float64(v) / 100000.0
+
+	return voltage, nil
+}
+
+func (d *INA219) Voltage() (float64, error) {
+	if err := d.setup(); err != nil {
+		return math.NaN(), err
+	}
+
+	v, err := d.Bus.ReadWordFromReg(d.address, busVReg)
+	if err != nil {
+		return math.NaN(), err
+	}
+
+	voltage := float64(v>>3) / 250.0
+
+	return voltage, nil
+}
+
+func (d *INA219) Current() (float64, error) {
+	if err := d.setup(); err != nil {
+		return math.NaN(), err
+	}
+
+	v, err := d.Bus.ReadWordFromReg(d.address, currentReg)
+	if err != nil {
+		return math.NaN(), err
+	}
+
+	current := float64(v) / 1000.0
+
+	return current, nil
+}
+
+// Close
+func (d *INA219) Close() error {
+	// put in power down mode
+	config := uint16(0x0000)
+	err := d.Bus.WriteWordToReg(d.address, configReg, config)
+	if err != nil {
+		return err
+	}
+	return nil
+}