Add support for reading battery voltage

mqtt.go

@@ -73,6 +73,12 @@ func (m *MQTT) Publish(name string, r *Reading) {
 		value := fmt.Sprintf("%04f", r.Humidity)
 		m.publish(topic, value)
 	}
+	// Publish Battery voltage
+	{
+		topic := fmt.Sprintf(format, m.id, name, "battery")
+		value := fmt.Sprintf("%04f", r.Battery)
+		m.publish(topic, value)
+	}
 }
 func (m *MQTT) publish(topic string, payload interface{}) {
 	log.Printf("[MQTT:publish] %s (%v)", topic, payload)

reading.go

@@ -10,47 +10,55 @@ import (
 type Reading struct {
 	Temperature float64
 	Humidity    float64
+    Battery     float64
 }
 
 // Equal determine whether one Reading is equal to another
 func (r *Reading) Equal(s Reading) bool {
-	log.Printf("[Reading:Equal] Temperatures: %f (%f); Humidity: %f (%f)", r.Temperature, s.Temperature, r.Humidity, s.Humidity)
+    log.Printf("[Reading:Equal] Temperatures: %f (%f); Humidity: %f (%f); Battery: %f (%f)", r.Temperature, s.Temperature, r.Humidity, s.Humidity, r.Battery, s.Battery)
 	if r.Temperature != s.Temperature {
 		log.Print("[Reading:Equal] Temperatures don't match")
 	}
 	if r.Humidity != s.Humidity {
 		log.Print("[Reading:Equal] Humidities don't match")
 	}
-	return r.Temperature == s.Temperature && r.Humidity == s.Humidity
+	if r.Battery != s.Battery {
+		log.Print("[Reading:Equal] Battery voltages don't match")
+	}
+	return r.Temperature == s.Temperature && r.Humidity == s.Humidity && r.Battery == s.Battery
 }
 
 // ToString converts a Reading to a string
 func (r *Reading) String() string {
-	return fmt.Sprintf("Temperature: %.04f; Humidity: %.04f", r.Temperature, r.Humidity)
+	return fmt.Sprintf("Temperature: %.04f; Humidity: %.04f; Battery: %.04f", r.Temperature, r.Humidity, r.Battery)
 }
 
 // NewReading returns a new Reading
-func NewReading(t, h float64) *Reading {
+func NewReading(t, h, v float64) *Reading {
 	return &Reading{
 		Temperature: t,
 		Humidity:    h,
+		Battery:    v,
 	}
 }
 
 // Unmarshall converts an encoded reading into a Reading
 func Unmarshall(req []byte) (*Reading, error) {
 	// 00 01 02 03 04
-	// T2 T1 HX ?? ??
+	// T2 T1 HX V2 V1
 	l := len(req)
 	if l != 5 {
 		log.Printf("[X] Expecting 5 bytes; got %d", l)
 		return &Reading{}, fmt.Errorf("Expecting 5 bytes got %d", l)
 	}
-	// Temperature is stored little endian
+	// Temperature is stored little endian *100
 	t := float64(int(binary.LittleEndian.Uint16(req[0:2]))) / 100.0
 	h := float64(req[2]) / 100.0
+	// Battery voltage is stored little endian * 1000
+	v := float64(int(binary.LittleEndian.Uint16(req[3:5]))) / 1000.0
 	return &Reading{
 		Temperature: t,
 		Humidity:    h,
+        Battery:     v,
 	}, nil
 }