Improvements for noise immunity. Closes #33.

Author: JChristensen

library.properties

@@ -1,9 +1,9 @@
 name=JC_Button
-version=2.1.4
+version=2.1.5
 author=Jack Christensen <jack.christensen@outlook.com>
 maintainer=Jack Christensen <jack.christensen@outlook.com>
 sentence=Arduino library to debounce button switches, detect presses, releases, and long presses.
-paragraph=Copyright (C) 2018-2019 by Jack Christensen and licensed under GNU GPL v3.0.
+paragraph=Copyright (C) 2018-2024 by Jack Christensen and licensed under GNU GPL v3.0.
 category=Signal Input/Output
 url=https://github.com/JChristensen/JC_Button
 architectures=*

src/JC_Button.cpp

@@ -21,18 +21,32 @@ void Button::begin()
 // does debouncing, captures and maintains times, previous state, etc.
 bool Button::read()
 {
-    uint32_t ms = millis();
+    m_time = millis();
     bool pinVal = digitalRead(m_pin);
     if (m_invert) pinVal = !pinVal;
-    if (ms - m_lastChange < m_dbTime) {
-        m_changed = false;
-    }
-    else {
-        m_lastState = m_state;
-        m_state = pinVal;
-        m_changed = (m_state != m_lastState);
-        if (m_changed) m_lastChange = ms;
+
+    switch (m_fsm) {
+        case STABLE:
+            if (pinVal != m_state) {    // maybe a change, but debounce first
+                m_dbStart = m_time;
+                m_fsm = DEBOUNCE;
+            }
+            else {                      // nothing to see here
+                m_changed = false;
+            }
+            break;
+
+        case DEBOUNCE:
+            if (m_time - m_dbStart >= m_dbTime) {
+                m_fsm = STABLE;
+                if (pinVal != m_state) {    // a real change (else just noise)
+                    m_lastState = m_state;
+                    m_state = pinVal;
+                    m_lastChange = m_time;
+                    m_changed = true;
+                }
+            }
+            break;
     }
-    m_time = ms;
     return m_state;
 }

src/JC_Button.h

@@ -60,15 +60,18 @@ class Button
         uint32_t lastChange() const {return m_lastChange;}
 
     private:
+        enum fsmStates_t {STABLE, DEBOUNCE};    // states for the state machine
+        fsmStates_t m_fsm {STABLE};             // initial state machine state
         uint8_t m_pin;                  // arduino pin number connected to button
         uint32_t m_dbTime;              // debounce time (ms)
         bool m_puEnable;                // internal pullup resistor enabled
         bool m_invert;                  // if true, interpret logic low as pressed, else interpret logic high as pressed
-        bool m_state = false;           // current button state, true=pressed
-        bool m_lastState = false;       // previous button state
-        bool m_changed = false;         // state changed since last read
-        uint32_t m_time = 0;            // time of current state (ms from millis)
-        uint32_t m_lastChange = 0;      // time of last state change (ms)
+        bool m_state {false};           // current button state, true=pressed
+        bool m_lastState {false};       // previous button state
+        bool m_changed {false};         // state changed since last read
+        uint32_t m_time {0};            // time of current state (ms from millis)
+        uint32_t m_lastChange {0};      // time of last state change (ms)
+        uint32_t m_dbStart;             // debounce interval start time
 };
 
 // a derived class for a "push-on, push-off" (toggle) type button.