makeybutton: revise to better match the algorithm defined by the original

Signed-off-by: deadprogram <ron@hybridgroup.com>

makeybutton/button.go

@@ -4,6 +4,8 @@
 // Inspired by the amazing MakeyMakey
 // https://makeymakey.com/
 //
+// This code is a reinterpretation of
+// https://github.com/sparkfun/MaKeyMaKey/blob/master/firmware/Arduino/makey_makey/makey_makey.ino
 package makeybutton
 
 import (
@@ -11,6 +13,11 @@ import (
 	"time"
 )
 
+var (
+	pressThreshold   int = 1
+	releaseThreshold int = 0
+)
+
 // ButtonState represents the state of a MakeyButton.
 type ButtonState int
 
@@ -33,6 +40,7 @@ const (
 type Button struct {
 	pin              machine.Pin
 	state            ButtonState
+	pressed          bool
 	readings         *Buffer
 	HighMeansPressed bool
 }
@@ -49,7 +57,7 @@ func NewButton(pin machine.Pin) *Button {
 
 // Configure configures the Makey Button pin to have the correct settings to detect touches.
 func (b *Button) Configure() error {
-	// Note that we have to first turn on the pullup, and then turn off the pullup,
+	// Note that on AVR we have to first turn on the pullup, and then turn off the pullup,
 	// in order for the pin to be properly floating.
 	b.pin.Configure(machine.PinConfig{Mode: machine.PinInputPullup})
 	time.Sleep(10 * time.Millisecond)
@@ -62,30 +70,36 @@ func (b *Button) Configure() error {
 // Get returns a ButtonEvent based on the most recent state of the button,
 // and if it has changed by being pressed or released.
 func (b *Button) Get() ButtonEvent {
-	// if pin is pulled up, a low value means the key is pressed
-	pressed := !b.pin.Get()
-	if b.HighMeansPressed {
-		// otherwise, a high value means the key is pressed
-		pressed = !pressed
-	}
+	b.update()
 
-	avg := b.readings.Avg()
-	b.readings.Put(pressed)
-
-	switch {
-	case pressed && avg > -1*bufferSize+2:
-		if b.state == Press {
-			return NotChanged
-		}
-
-		b.state = Press
-		return Pressed
-	case !pressed:
-		if b.state == Press {
+	if b.pressed {
+		// the button had previously been pressed,
+		// but now appears to have been released.
+		if b.readings.Sum() <= releaseThreshold {
+			b.pressed = false
 			b.state = Release
 			return Released
 		}
+	} else {
+		// the button had previously not been pressed,
+		// but now appears to have been pressed.
+		if b.readings.Sum() >= pressThreshold {
+			b.pressed = true
+			b.state = Press
+			return Pressed
+		}
 	}
 
 	return NotChanged
 }
+
+func (b *Button) update() {
+	// if pin is pulled up, a low value means the key is pressed
+	press := !b.pin.Get()
+	if b.HighMeansPressed {
+		// otherwise, a high value means the key is pressed
+		press = !press
+	}
+
+	b.readings.Put(press)
+}