Add sensor weight

cmd/fermentord/db.go

@@ -55,7 +55,7 @@ func persistData(ctx context.Context, wg *sync.WaitGroup, chState <-chan control
 				break
 			}
 
-			err := datlog("%v TEMP %v %v", t.Time.Unix(), t.Sensor, t.MilliDegrees)
+			err := datlog("%v TEMP %v %v", t.Time.Unix(), t.Sensor, t.Degrees)
 			if err != nil {
 				hub.CaptureException(err)
 				log.Printf("Error persisting temperature reading: %v", err)

cmd/fermentord/main.go

@@ -56,7 +56,7 @@ func mainLoop(ctx context.Context, wg *sync.WaitGroup, js nats.JetStream, config
 	wg.Add(3)
 	go persistData(ctx, wg, chDbState, chDbTemp, config)
 	go ctrl.Run(ctx, wg)
-	go temperature.PollSensors(ctx, wg, 1*time.Second)
+	go temperature.PollSensors(ctx, wg, 1*time.Second, config.Sensors.Weight)
 
 	for {
 		select {

internal/controllers/chamber.go

@@ -89,18 +89,18 @@ func (p *ChamberController) Run(ctx context.Context, wg *sync.WaitGroup) {
 
 func (p *ChamberController) setTemperature(t temperature.TemperatureReading) {
 	switch t.Sensor {
-	case p.config.Sensor.Ambient:
-		p.ambientTemperature = t.Degrees()
+	case p.config.Sensors.Ambient:
+		p.ambientTemperature = t.Degrees
 
-	case p.config.Sensor.Chamber:
-		p.chamberTemperature = t.Degrees()
+	case p.config.Sensors.Chamber:
+		p.chamberTemperature = t.Degrees
 
-	case p.config.Sensor.Wort:
-		p.wortTemperature = t.Degrees()
+	case p.config.Sensors.Wort:
+		p.wortTemperature = t.Degrees
 
 	default:
-		log.Printf("Unknown sensor: sensor=%v temp=%v", t.Sensor, t.MilliDegrees)
-		p.hub.CaptureMessage(fmt.Sprintf("Unknown sensor: sensor=%v temp=%v", t.Sensor, t.MilliDegrees))
+		log.Printf("Unknown sensor: sensor=%v temp=%v", t.Sensor, t.Degrees)
+		p.hub.CaptureMessage(fmt.Sprintf("Unknown sensor: sensor=%v temp=%v", t.Sensor, t.Degrees))
 	}
 }
 

internal/controllers/config.go

@@ -16,10 +16,11 @@ type ControllerConfig struct {
 
 	DataPath string `mapstructure:"data_path"`
 
-	Sensor struct {
+	Sensors struct {
 		Wort    string  `mapstructure:"wort"`
 		Chamber string  `mapstructure:"chamber"`
 		Ambient string  `mapstructure:"ambient"`
+		Weight  float64 `mapstructure:"weight"`
 	} `mapstructure:"sensors"`
 
 	FermentationTemperature float64 `mapstructure:"fermentation_temp"`

pkg/temperature/ds18b20.go

@@ -36,16 +36,18 @@ var (
 	sensors       []string
 	accErrTrigger int
 	accErrSensor  map[string]int
+	filters       map[string]*EWMAFilter
 )
 
 func Initialize() {
 	sensors = make([]string, 0)
+	filters = make(map[string]*EWMAFilter)
 	C = make(chan TemperatureReading, 30)
 	ConfigUpdates = make(chan []string, 1)
 	accErrSensor = make(map[string]int)
 }
 
-func PollSensors(ctx context.Context, wg *sync.WaitGroup, readingInterval time.Duration) {
+func PollSensors(ctx context.Context, wg *sync.WaitGroup, readingInterval time.Duration, filterWeight float64) {
 	hub := sentry.CurrentHub().Clone()
 	defer hub.Flush(10 * time.Second)
 	defer wg.Done()
@@ -95,6 +97,13 @@ func PollSensors(ctx context.Context, wg *sync.WaitGroup, readingInterval time.D
 		case c := <-ConfigUpdates:
 			sensors = c
 
+			for k := range filters {
+				delete(filters, k)
+			}
+			for _, x := range sensors {
+				filters[x] = NewEWMAFilter(filterWeight)
+			}
+
 		case <-ctx.Done():
 			close(C)
 			return
@@ -115,16 +124,17 @@ func readSensors(hub *sentry.Hub) {
 		}
 
 		accErrSensor[sensor] = 0
+		tw := filters[sensor].Update(float64(t) / 1000)
 
 		r := TemperatureReading{
 			Time:    time.Now(),
 			Sensor:  sensor,
-			MilliDegrees: t,
+			Degrees: tw,
 		}
 
 		metrics.TemperatureSensorReadingDegreesCelcius.
 			WithLabelValues(sensor).
-			Set(r.Degrees())
+			Set(tw)
 
 		C <- r
 

pkg/temperature/filter.go

@@ -0,0 +1,28 @@
+package temperature
+
+// EWMAFilter is an exponentially weighted moving average filter
+// See https://hackaday.com/2019/09/06/sensor-filters-for-coders/
+type EWMAFilter struct {
+	weight        float64
+	prevTemp      float64
+	isInitialized bool
+}
+
+func NewEWMAFilter(weight float64) *EWMAFilter {
+	return &EWMAFilter{
+		weight: weight,
+	}
+}
+
+func (p *EWMAFilter) Update(input float64) float64 {
+	if !p.isInitialized {
+		p.prevTemp = input
+		p.isInitialized = true
+		return input
+	}
+
+	ewmf := (1-p.weight)*p.prevTemp + p.weight*input
+	p.prevTemp = ewmf
+
+	return ewmf
+}

pkg/temperature/temperature.go

@@ -5,9 +5,5 @@ import "time"
 type TemperatureReading struct {
 	Sensor  string    `json:"sensor"`
 	Time    time.Time `json:"time"`
-	MilliDegrees int64     `json:"milli_degrees"`
-}
-
-func (t *TemperatureReading) Degrees() float64 {
-	return float64(t.MilliDegrees) / 1000.0
+	Degrees float64   `json:"degrees"`
 }