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+<!--
+title: Yet Another Debouncing Method
+date: 2018-04-30
+-->
+
+You can find several approaches for debouncing mechanical switches on the Internet, some work better, some not so good.
+
+One common approach is to ignore events in an ISR when they come too fast:<
+
+```
+void count() {
+	static uint32_t lastEvent = 0;
+	uint32_t currentEvent = micros();
+	if (currentEvent &gt; (lastEvent + configBlock.debounce)) {
+		lastEvent = currentEvent;
+		cnt++;
+	}
+}
+
+void setup() {
+        pinMode(REED_PIN, INPUT_PULLUP);
+        attachInterrupt(REED_PIN, count, FALLING);
+}
+```
+
+This works very good when only the tipping of a switch is relevant.
+
+When also the time the button was pressed is relevant and when it is especially necessary to distinguish between a short and a long press this approach doesn't work anymore.
+
+Since I couldn't remember the approaches I read about earlier I've sketched this state machine:
+
+![](/static/20180430110848869_0001.jpg)
+
+(The double-lined states are action-states which send out the related information.)
+
+At least for me, this approach is working very reliable so far, I'm quite happy with it.
+
+```
+enum tPressedState { psHIGH, psLOW, psACCEPTED_LOW, psLONG_START, psLONG_CONT, psLONG_CONT_SEND, psLONG_END, psSHORT, psINVALID };
+
+typedef struct {
+	uint8_t index;
+	uint8_t buttonPin;
+	tPressedState pressedState;
+	tPressedState oldPressedState;
+	uint32_t lastStateChange;
+} tButton;
+
+tButton buttons[] = {
+					  { 1, SWITCH_1, psHIGH, psINVALID, 0 },
+					  { 2, SWITCH_2, psHIGH, psINVALID, 0 },
+					  { 3, SWITCH_3, psHIGH, psINVALID, 0 },
+					  { 0, 0, psINVALID, psINVALID, 0 } // END MARKER
+};
+
+static void buttonHandler(tButton *button) {
+	uint32_t currentMicros = micros();
+	uint8_t buttonState = digitalRead(button-&gt;buttonPin);
+
+#ifdef DEBUG
+	if (button-&gt;oldPressedState != button-&gt;pressedState) {
+		Serial.print("Index ");
+		Serial.print(button-&gt;index);
+		Serial.print(", state changed from ");
+		Serial.print(button-&gt;oldPressedState);
+		Serial.print(" to ");
+		Serial.print(button-&gt;pressedState);
+		Serial.println();
+		button-&gt;oldPressedState = button-&gt;pressedState;
+	}
+#endif
+
+	switch (button-&gt;pressedState) {
+	case psHIGH:
+		if (buttonState == LOW) {
+			button-&gt;pressedState = psLOW;
+			button-&gt;lastStateChange = currentMicros;
+		}
+		break;
+	case psLOW:
+		if (buttonState == HIGH) {
+			button-&gt;pressedState = psHIGH;
+			button-&gt;lastStateChange = currentMicros;
+		} else {
+			if (currentMicros &gt; (button-&gt;lastStateChange + configBlock.debounce)) {
+				button-&gt;pressedState = psACCEPTED_LOW;
+				button-&gt;lastStateChange = currentMicros;
+			}
+		}
+		break;
+	case psACCEPTED_LOW:
+		if (buttonState == HIGH) {
+			button-&gt;pressedState = psSHORT;
+			button-&gt;lastStateChange = currentMicros;
+		}
+		if (currentMicros &gt; (button-&gt;lastStateChange + (configBlock.longPress * 1000))) {
+			button-&gt;pressedState = psLONG_START;
+			button-&gt;lastStateChange = currentMicros;
+		}
+		break;
+	case psSHORT:
+		sendMsg(button-&gt;index, "PRESS_SHORT");
+		button-&gt;pressedState = psHIGH;
+		button-&gt;lastStateChange = currentMicros;
+		break;
+	case psLONG_START:
+		sendMsg(button-&gt;index, "PRESS_LONG_START");
+		button-&gt;pressedState = psLONG_CONT;
+		button-&gt;lastStateChange = currentMicros;
+		break;
+	case psLONG_CONT:
+		if (buttonState == HIGH) {
+			button-&gt;pressedState = psLONG_END;
+			button-&gt;lastStateChange = currentMicros;
+		}
+		if (currentMicros &gt; (button-&gt;lastStateChange + (configBlock.longPressRepeat * 1000))) {
+			button-&gt;pressedState = psLONG_CONT_SEND;
+			button-&gt;lastStateChange = currentMicros;
+		}
+		break;
+	case psLONG_CONT_SEND:
+		sendMsg(button-&gt;index, "PRESS_LONG_CONT");
+		button-&gt;pressedState = psLONG_CONT;
+		button-&gt;lastStateChange = currentMicros;
+		break;
+	case psLONG_END:
+		sendMsg(button-&gt;index, "PRESS_LONG_END");
+		button-&gt;pressedState = psHIGH;
+		button-&gt;lastStateChange = currentMicros;
+		break;
+	default:
+		button-&gt;pressedState = psHIGH;
+		button-&gt;lastStateChange = currentMicros;
+	}
+}
+```
+