Wolfgang Hottgenroth
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<meta property="og:site_name" content="Minimal Setups">
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<meta property="og:title" content="Yet Another Debouncing Method">
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<meta property="og:description" content="You can find several approaches for debouncing mechanical switches on the Internet, some work better, some not so good.
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One common approach is to ignore events in an ISR when they come too fast:<
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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.">
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<meta property="article:published_time" content="2018-04-30T00:00:00+00:00">
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<meta name="twitter:title" content="Yet Another Debouncing Method">
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<meta name="twitter:description" content="You can find several approaches for debouncing mechanical switches on the Internet, some work better, some not so good.
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One common approach is to ignore events in an ISR when they come too fast:<
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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.">
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<meta itemprop="name" content="Yet Another Debouncing Method">
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<meta itemprop="description" content="You can find several approaches for debouncing mechanical switches on the Internet, some work better, some not so good.
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One common approach is to ignore events in an ISR when they come too fast:<
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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.">
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<h1>Minimal Setups</h1>
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<li class=""><a href="/keys/">Keys</a></li>
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<li class=""><a href="/about/">About</a></li></ul>
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<main><h1>Yet Another Debouncing Method</h1>
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<time>Mon, Apr 30, 2018</time><p>You can find several approaches for debouncing mechanical switches on the Internet, some work better, some not so good.</p>
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<p>One common approach is to ignore events in an ISR when they come too fast:<</p>
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<pre tabindex="0"><code>void count() {
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static uint32_t lastEvent = 0;
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uint32_t currentEvent = micros();
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if (currentEvent &gt; (lastEvent + configBlock.debounce)) {
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lastEvent = currentEvent;
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cnt++;
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}
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}
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void setup() {
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pinMode(REED_PIN, INPUT_PULLUP);
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attachInterrupt(REED_PIN, count, FALLING);
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}
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</code></pre><p>This works very good when only the tipping of a switch is relevant.</p>
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<p>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.</p>
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<p>Since I couldn’t remember the approaches I read about earlier I’ve sketched this state machine:</p>
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<p><img src="/20180430110848869_0001.jpg" alt=""></p>
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<p>(The double-lined states are action-states which send out the related information.)</p>
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<p>At least for me, this approach is working very reliable so far, I’m quite happy with it.</p>
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<pre tabindex="0"><code>enum tPressedState { psHIGH, psLOW, psACCEPTED_LOW, psLONG_START, psLONG_CONT, psLONG_CONT_SEND, psLONG_END, psSHORT, psINVALID };
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typedef struct {
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uint8_t index;
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uint8_t buttonPin;
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tPressedState pressedState;
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tPressedState oldPressedState;
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uint32_t lastStateChange;
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} tButton;
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tButton buttons[] = {
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{ 1, SWITCH_1, psHIGH, psINVALID, 0 },
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{ 2, SWITCH_2, psHIGH, psINVALID, 0 },
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{ 3, SWITCH_3, psHIGH, psINVALID, 0 },
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{ 0, 0, psINVALID, psINVALID, 0 } // END MARKER
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};
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static void buttonHandler(tButton *button) {
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uint32_t currentMicros = micros();
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uint8_t buttonState = digitalRead(button-&gt;buttonPin);
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#ifdef DEBUG
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if (button-&gt;oldPressedState != button-&gt;pressedState) {
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Serial.print("Index ");
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Serial.print(button-&gt;index);
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Serial.print(", state changed from ");
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Serial.print(button-&gt;oldPressedState);
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Serial.print(" to ");
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Serial.print(button-&gt;pressedState);
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Serial.println();
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button-&gt;oldPressedState = button-&gt;pressedState;
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}
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#endif
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switch (button-&gt;pressedState) {
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case psHIGH:
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if (buttonState == LOW) {
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button-&gt;pressedState = psLOW;
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button-&gt;lastStateChange = currentMicros;
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}
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break;
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case psLOW:
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if (buttonState == HIGH) {
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button-&gt;pressedState = psHIGH;
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button-&gt;lastStateChange = currentMicros;
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} else {
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if (currentMicros &gt; (button-&gt;lastStateChange + configBlock.debounce)) {
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button-&gt;pressedState = psACCEPTED_LOW;
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button-&gt;lastStateChange = currentMicros;
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}
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}
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break;
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case psACCEPTED_LOW:
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if (buttonState == HIGH) {
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button-&gt;pressedState = psSHORT;
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button-&gt;lastStateChange = currentMicros;
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}
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if (currentMicros &gt; (button-&gt;lastStateChange + (configBlock.longPress * 1000))) {
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button-&gt;pressedState = psLONG_START;
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button-&gt;lastStateChange = currentMicros;
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}
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break;
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case psSHORT:
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sendMsg(button-&gt;index, "PRESS_SHORT");
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button-&gt;pressedState = psHIGH;
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button-&gt;lastStateChange = currentMicros;
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break;
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case psLONG_START:
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sendMsg(button-&gt;index, "PRESS_LONG_START");
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button-&gt;pressedState = psLONG_CONT;
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button-&gt;lastStateChange = currentMicros;
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break;
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case psLONG_CONT:
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if (buttonState == HIGH) {
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button-&gt;pressedState = psLONG_END;
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button-&gt;lastStateChange = currentMicros;
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}
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if (currentMicros &gt; (button-&gt;lastStateChange + (configBlock.longPressRepeat * 1000))) {
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button-&gt;pressedState = psLONG_CONT_SEND;
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button-&gt;lastStateChange = currentMicros;
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}
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break;
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case psLONG_CONT_SEND:
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sendMsg(button-&gt;index, "PRESS_LONG_CONT");
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button-&gt;pressedState = psLONG_CONT;
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button-&gt;lastStateChange = currentMicros;
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break;
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case psLONG_END:
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sendMsg(button-&gt;index, "PRESS_LONG_END");
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button-&gt;pressedState = psHIGH;
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button-&gt;lastStateChange = currentMicros;
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break;
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default:
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button-&gt;pressedState = psHIGH;
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button-&gt;lastStateChange = currentMicros;
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}
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}
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</code></pre><footer>
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