diff --git a/libraries/I2CKeyPad8x8/CHANGELOG.md b/libraries/I2CKeyPad8x8/CHANGELOG.md
index 71826f3a..ffd937a8 100644
--- a/libraries/I2CKeyPad8x8/CHANGELOG.md
+++ b/libraries/I2CKeyPad8x8/CHANGELOG.md
@@ -6,16 +6,29 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/)
 and this project adheres to [Semantic Versioning](http://semver.org/).
 
 
+## [0.3.0] - 2024-07-15
+- sync with I2CKeyPad 0.5.0
+- implement **debounceThreshold**
+- add constant **I2C_KEYPAD8x8_THRESHOLD**
+- add **uint32_t getLastTimeRead()**
+- update **getChar()** to support **I2C_KEYPAD8x8_THRESHOLD**
+- update readme.md
+- update unit test
+- update keywords.txt
+- minor edits
+
+----
+
 ## [0.2.0] - 2023-11-09
 - simplify begin()
 - update readme.md
-- minor edits.
+- minor edits
 
+----
 
 ## [0.1.1] - 2022-11-12
 - Add RP2040 support to build-CI.
 - Add CHANGELOG.md
 
-
 ## [0.1.0] - 2022-09-29
 - initial version
diff --git a/libraries/I2CKeyPad8x8/I2CKeyPad8x8.cpp b/libraries/I2CKeyPad8x8/I2CKeyPad8x8.cpp
index e73cf9db..4d0801da 100644
--- a/libraries/I2CKeyPad8x8/I2CKeyPad8x8.cpp
+++ b/libraries/I2CKeyPad8x8/I2CKeyPad8x8.cpp
@@ -1,7 +1,7 @@
 //
 //    FILE: I2CKeyPad8x8.cpp
 //  AUTHOR: Rob Tillaart
-// VERSION: 0.2.0
+// VERSION: 0.3.0
 // PURPOSE: Arduino library for 8x8 or smaller KeyPad connected to an I2C PCF8575.
 //     URL: https://github.com/RobTillaart/I2CKeyPad8x8
 
@@ -14,6 +14,8 @@ I2CKeyPad8x8::I2CKeyPad8x8(const uint8_t deviceAddress, TwoWire *wire)
   _lastKey = I2C_KEYPAD8x8_NOKEY;
   _address = deviceAddress;
   _wire    = wire;
+  _debounceThreshold = 0;
+  _lastTimeRead = 0;
 }
 
 
@@ -33,6 +35,106 @@ bool I2CKeyPad8x8::isConnected()
 
 
 uint8_t I2CKeyPad8x8::getKey()
+{
+  uint32_t now = millis();
+  if (_debounceThreshold > 0)
+  {
+    if (now - _debounceThreshold < _lastTimeRead)
+    {
+      return I2C_KEYPAD8x8_THRESHOLD;
+    }
+  }
+
+  uint8_t key = _getKey8x8();
+  if (key == I2C_KEYPAD8x8_FAIL) return key;  //  propagate error.
+  //  valid keys + NOKEY
+  _lastKey = key;
+  _lastTimeRead = now;
+  return key;
+}
+
+
+uint8_t I2CKeyPad8x8::getLastKey()
+{
+  return _lastKey;
+}
+
+
+//  to check "press any key"
+bool I2CKeyPad8x8::isPressed()
+{
+  uint16_t a = _read(0xFF00);
+  if (a == 0xFF00) return false;
+  return (a != 0xFF00);
+}
+
+
+uint8_t I2CKeyPad8x8::getChar()
+{
+  uint8_t key = getKey();
+  if (key != I2C_KEYPAD8x8_THRESHOLD)
+  {
+    return _keyMap[key];
+  }
+  return I2C_KEYPAD8x8_THRESHOLD;
+}
+
+
+uint8_t I2CKeyPad8x8::getLastChar()
+{
+  return _keyMap[_lastKey];
+}
+
+
+void I2CKeyPad8x8::loadKeyMap(char * keyMap)
+{
+  _keyMap = keyMap;
+}
+
+
+void I2CKeyPad8x8::setDebounceThreshold(uint16_t value)
+{
+  _debounceThreshold = value;
+}
+
+
+uint16_t I2CKeyPad8x8::getDebounceThreshold()
+{
+  return _debounceThreshold;
+}
+
+
+uint32_t I2CKeyPad8x8::getLastTimeRead()
+{
+  return _lastTimeRead;
+}
+
+
+//////////////////////////////////////////////////////
+//
+//  PROTECTED
+//
+uint16_t I2CKeyPad8x8::_read(uint16_t mask)
+{
+  //  improve the odds that IO will not interrupted.
+  yield();
+
+  _wire->beginTransmission(_address);
+  _wire->write(mask >> 8);
+  _wire->write(mask & 0xFF);
+  if (_wire->endTransmission() != 0)
+  {
+    //  set communication error
+    return 0xFFFF;
+  }
+  _wire->requestFrom(_address, (uint8_t)2);
+  uint16_t value = _wire->read() << 8;
+  value += _wire->read();
+  return value;
+}
+
+
+uint8_t I2CKeyPad8x8::_getKey8x8()
 {
   //  key = row + 8 x col
   uint8_t key = 0;
@@ -66,68 +168,9 @@ uint8_t I2CKeyPad8x8::getKey()
   else if (cols == 0x007F) key += 56;
   else return I2C_KEYPAD8x8_FAIL;
 
-  _lastKey = key;
-
   return key;   // 0..65
 }
 
 
-uint8_t I2CKeyPad8x8::getLastKey()
-{
-  return _lastKey;
-};
-
-
-//  to check "press any key"
-bool I2CKeyPad8x8::isPressed()
-{
-  uint16_t a = _read(0xFF00);
-  if (a == 0xFF00) return false;
-  return (a != 0xFF00);
-}
-
-
-uint8_t I2CKeyPad8x8::getChar()
-{
-  return _keyMap[getKey()];
-};
-
-
-uint8_t I2CKeyPad8x8::getLastChar()
-{
-  return _keyMap[_lastKey];
-};
-
-
-void I2CKeyPad8x8::loadKeyMap(char * keyMap)
-{
-  _keyMap = keyMap;
-}
-
-
-//////////////////////////////////////////////////////
-//
-//  PROTECTED
-//
-uint16_t I2CKeyPad8x8::_read(uint16_t mask)
-{
-  //  improve the odds that IO will not interrupted.
-  yield();
-
-  _wire->beginTransmission(_address);
-  _wire->write(mask >> 8);
-  _wire->write(mask & 0xFF);
-  if (_wire->endTransmission() != 0)
-  {
-    //  set communication error
-    return 0xFFFF;
-  }
-  _wire->requestFrom(_address, (uint8_t)2);
-  uint16_t value = _wire->read() << 8;
-  value += _wire->read();
-  return value;
-}
-
-
 //  -- END OF FILE --
 
diff --git a/libraries/I2CKeyPad8x8/I2CKeyPad8x8.h b/libraries/I2CKeyPad8x8/I2CKeyPad8x8.h
index 1010a6d1..5ea7f21c 100644
--- a/libraries/I2CKeyPad8x8/I2CKeyPad8x8.h
+++ b/libraries/I2CKeyPad8x8/I2CKeyPad8x8.h
@@ -2,7 +2,7 @@
 //
 //    FILE: I2CKeyPad8x8.h
 //  AUTHOR: Rob Tillaart
-// VERSION: 0.2.0
+// VERSION: 0.3.0
 // PURPOSE: Arduino library for 8x8 or smaller KeyPad connected to an I2C PCF8575.
 //     URL: https://github.com/RobTillaart/I2CKeyPad
 
@@ -11,17 +11,18 @@
 #include "Wire.h"
 
 
-#define I2C_KEYPAD8x8_LIB_VERSION         (F("0.2.0"))
+#define I2C_KEYPAD8x8_LIB_VERSION         (F("0.3.0"))
 
 #define I2C_KEYPAD8x8_NOKEY               64
 #define I2C_KEYPAD8x8_FAIL                65
-
+#define I2C_KEYPAD8x8_THRESHOLD           255
 
 class I2CKeyPad8x8
 {
 public:
   I2CKeyPad8x8(const uint8_t deviceAddress, TwoWire *wire = &Wire);
 
+  //  call Wire.begin() first!
   bool     begin();
   bool     isConnected();
 
@@ -30,22 +31,31 @@ public:
   uint8_t  getLastKey();
   bool     isPressed();
 
-
   //  get 'translated' keys
   //  user must load KeyMap, there is no check.
   uint8_t  getChar();
   uint8_t  getLastChar();
   void     loadKeyMap(char * keyMap);   //  char[65]
 
+  //  value in milliseconds, max 65535 ms
+  void     setDebounceThreshold(uint16_t value = 0);
+  uint16_t getDebounceThreshold();
+  uint32_t getLastTimeRead();
+
 
 protected:
   uint8_t  _address;
   uint8_t  _lastKey;
   uint16_t _read(uint16_t mask);
+  uint16_t _debounceThreshold;
+  uint32_t _lastTimeRead;
+
+  uint8_t  _getKey8x8();
 
   TwoWire* _wire;
 
   char *   _keyMap = NULL;
+
 };
 
 
diff --git a/libraries/I2CKeyPad8x8/README.md b/libraries/I2CKeyPad8x8/README.md
index 302a0a61..3668822c 100644
--- a/libraries/I2CKeyPad8x8/README.md
+++ b/libraries/I2CKeyPad8x8/README.md
@@ -21,11 +21,20 @@ EXPERIMENTAL (first tests ==> OK)
 The I2CKeyPad8x8 library implements the reading of a 8x8 keypad by means of a PCF8575.
 Smaller keypads, meaning less columns or rows (e.g. 5x4) can be read with it too.
 
-#### Related
+### Breaking change
 
-Relates strongly to https://github.com/RobTillaart/I2CKeyPad. which is an 8x8 version using **PCF8574**.
+Since 0.3.0 the library can set a debounce threshold. 
+If this is set (> 0) the **getKey()** and **getChar()** functions 
+can return **I2C_KEYPAD_THRESHOLD** (255).
 
+
+### Related
+
+Relates strongly to https://github.com/RobTillaart/I2CKeyPad. which is an 4x4 version using **PCF8574**.
+
+- https://github.com/RobTillaart/PCF8575
 - https://github.com/RobTillaart/AnalogKeypad
+- https://github.com/RobTillaart/I2CKeyPad4x4
 - https://github.com/RobTillaart/I2CKeyPad8x8
 
 
@@ -36,30 +45,59 @@ See the conceptual schema below.
 It might take some trying to get the correct pins connected.
 
 ```
-          PROC             PCF8575              KEYPAD
-        +--------+        +--------+          +--------+
-        |        |        |       0|----------|R       |
-        |    SDA |--------|       .|----------|O       |
-        |    SCL |--------|       .|----------|W       |
-        |        |        |       7|----------|S       |
-        |        |        |       .|          |        |
-        |        |        |       .|          |        |
-        |        |        |       8|----------|C       |
-        |        |        |       .|----------|O       |
-        |        |        |       .|----------|L       |
-        |        |        |      15|----------|S       |
-        +--------+        +--------+          +--------+ 
+          PROC              PCF8575              KEYPAD
+        +--------+        +---------+          +---------+
+        |        |        |       0 |<-------->| R       |
+        |    SDA |<------>|       . |<-------->| O       |
+        |    SCL |<------>|       . |<-------->| W       |
+        |        |        |       7 |<-------->| S       |
+        |        |        |         |          |         |
+        |        |        |       8 |<-------->| C       |
+        |        |        |       . |<-------->| O       |
+        |        |        |       . |<-------->| L       |
+        |        |        |      15 |<-------->| S       |
+        +--------+        +---------+          +---------+ 
 ```
 
 
+## I2C
+
+### I2C addresses
+
+This library uses a PCF8575 chip.
+
+|  Type      |  Address-range  |  Notes                    |
+|:-----------|:---------------:|:-------------------------:|
+|  PCF8575   |  0x20 to 0x27   |  same range as PCF8574 !  |
+
+Be careful to select an unique I2C address for every device on the bus.
+
+
+### I2C multiplexing
+
+Sometimes you need to control more devices than possible with the default
+address range the device provides.
+This is possible with an I2C multiplexer e.g. TCA9548 which creates up
+to eight channels (think of it as I2C subnets) which can use the complete
+address range of the device.
+
+Drawback of using a multiplexer is that it takes more administration in
+your code e.g. which device is on which channel.
+This will slow down the access, which must be taken into account when
+deciding which devices are on which channel.
+Also note that switching between channels will slow down other devices
+too if they are behind the multiplexer.
+
+- https://github.com/RobTillaart/TCA9548
+
+
 ## Interface
 
 ```cpp
 #include "I2CKeyPad8x8.h"
 ```
 
-
-#### Base
+### Base
 
 - **I2CKeyPad8x8(const uint8_t deviceAddress, TwoWire \*wire = &Wire)** 
 The constructor sets the device address and optionally 
@@ -68,23 +106,28 @@ allows to selects the I2C bus to use.
 Call wire.begin() first!
 - **bool isConnected()** returns false if the PCF8575 cannot be connected to.
 - **uint8_t getKey()** Returns default 0..63 for regular keys, 
-Returns 64 if no key is pressed and 65 in case of an error.
-- **uint8_t getLastKey()** Returns the last **valid** key pressed 0..63. Initially it will return 64 (NOKEY).
-- **bool isPressed()** Returns true if one or more keys of the keyPad is pressed, 
-however it is not checked if multiple keys are pressed.
+Returns **I2C_KEYPAD8X8_NOKEY** (64) if no key is pressed and and **I2C_KEYPAD8X8_FAIL**
+(17) in case of an error, e.g. multiple keys pressed.
+If a debounce delay is set, it might return **I2C_KEYPAD8X8_THRESHOLD** if called too fast.
+- **uint8_t getLastKey()** Returns the last **valid** key pressed 0..63, or **I2C_KEYPAD8X8_NOKEY** (64) which is also the initial value.
+- **bool isPressed()** Returns true if one or more keys of the keyPad are pressed, 
+however there is no check if multiple keys are pressed.
 
 
-#### KeyMap functions
+### KeyMap functions
 
-**loadKeyMap()** must be called before **getChar()** and **getLastChar()**!
+Note: **loadKeyMap()** must be called before **getChar()** and **getLastChar()**!
 
 - **char getChar()** returns the char corresponding to mapped key pressed.
+It returns **I2C_KEYPAD_THRESHOLD** if called too fast.
 - **char getLastChar()** returns the last char pressed.
+This function is not affected by the debounce threshold.
 - **bool loadKeyMap(char \* keyMap)** keyMap should point to a (global) char array of length 66.
 This array maps index 0..63 on a char and index \[64\] maps to **I2CKeyPad8x8_NOKEY** (typical 'N') 
 and index \[65\] maps **I2CKeyPad8x8_FAIL** (typical 'F'). index 66 is the null char.
 
 **WARNING**
+
 If there is no key map loaded the user should **NOT** call **getChar()** or 
 **getLastChar()** as these would return meaningless bytes.
 
@@ -93,14 +136,49 @@ Note: a keyMap char array may be longer than 66 characters, but only the first 6
 The length is **NOT** checked upon loading (as it may contain a NULL char).
 
 
-#### Basic working
+### Debouncing threshold
+
+**Experimental**
+
+Since version 0.3.0, the library implements an experimental debounce threshold
+which is non-blocking.
+
+If a key bounces, it can trigger multiple interrupts, while the purpose is to
+act like only one keypress. The debounce threshold results in a fast return 
+of **getKey()** (with **I2C_KEYPAD8x8_THRESHOLD**) if called too fast.
+
+The default value of the debounce threshold is zero to be backwards compatible.
+The value is set in milliseconds, with a maximum of 65535 ==> about 65 seconds or 1 minute.
+A value of 1 still allows ~1000 **getKey()** calls per second (in theory).
+A value of 65535 can be used e.g. for a delay after entering a wrong key code / password.
+Setting a high value might result in missed keypresses so use with care.
+
+The default value of the debounce threshold is zero to be backwards compatible.
+
+- **void setDebounceThreshold(uint16_t value = 0)** set the debounce threshold,
+value in milliseconds, max 65535.
+The default value is zero, to reset its value.
+- **uint16_t getDebounceThreshold()** returns the set debounce threshold.
+- **uint32_t getLastTimeRead()** returns the time stamp of the last valid read key
+(or NOKEY). This variable is used for the debounce, and may be used for other
+purposes too. E.g. track time between keypresses.
+
+If a debounce threshold is set, and **getKey()** or **getChar()** is called too fast,
+these functions will return **I2C_KEYPAD8x8_THRESHOLD** (255).
+
+Feedback welcome!
+
+
+### Basic working
 
 After the **keypad.begin()** the sketch calls the **keyPad.getKey()** to read values from the keypad. 
 - If no key is pressed **I2C_KEYPAD8x8_NOKEY** code (16) is returned.
-- If the read value is not valid, e.g. two keys pressed, **I2CKeyPad8x8_FAIL** code (17) is returned.
+- If the read value is not valid, e.g. two keys pressed, **I2C_KEYPAD8x8_FAIL** code (17) is returned.
+- If a debounce threshold is set, **I2C_KEYPAD8x8_THRESHOLD** might be returned.
+See section above.
 - Otherwise a number 0..63 is returned.
 
-Note NOKEY and FAIL bot have bit 8 set, all valid keys don't.
+Note NOKEY and FAIL both have bit 8 set, all valid keys don't.
 This allows fast checking for valid keys.
 
 Only if a key map is loaded, the user can call **getChar()** and **getLastChar()** to get mapped keys.
@@ -109,19 +187,12 @@ Only if a key map is loaded, the user can call **getChar()** and **getLastChar()
 ## Interrupts
 
 The library enables the PCF8575 to generate interrupts on the PCF8575 when a key is pressed. 
-This makes checking the keypad far more efficient as one does not need to poll over I2C.
-
-See examples. (TODO)
-
-
-## Operation
-
-See examples
+This makes checking the keypad far more efficient as one does not need to poll the device over I2C.
+See examples.
 
 
 ## Future
 
-
 #### Must
 
 - update documentation
@@ -134,6 +205,8 @@ See examples
   - interrupts
   - keymapping
   - performance
+- improve error handling?
+  - **I2C_KEYPAD_ERR_MODE**
 
 #### Could
 
diff --git a/libraries/I2CKeyPad8x8/examples/I2Ckeypad8x8_demo01/I2Ckeypad8x8_demo01.ino b/libraries/I2CKeyPad8x8/examples/I2Ckeypad8x8_demo01/I2Ckeypad8x8_demo01.ino
index fccb49ce..03531e3b 100644
--- a/libraries/I2CKeyPad8x8/examples/I2Ckeypad8x8_demo01/I2Ckeypad8x8_demo01.ino
+++ b/libraries/I2CKeyPad8x8/examples/I2Ckeypad8x8_demo01/I2Ckeypad8x8_demo01.ino
@@ -13,7 +13,7 @@
 #include "Wire.h"
 #include "I2CKeyPad8x8.h"
 
-const uint8_t KEYPAD_ADDRESS = 0x38;
+const uint8_t KEYPAD_ADDRESS = 0x20;
 
 I2CKeyPad8x8 keyPad(KEYPAD_ADDRESS);
 
diff --git a/libraries/I2CKeyPad8x8/keywords.txt b/libraries/I2CKeyPad8x8/keywords.txt
index 81ed5b57..2c889420 100644
--- a/libraries/I2CKeyPad8x8/keywords.txt
+++ b/libraries/I2CKeyPad8x8/keywords.txt
@@ -16,6 +16,9 @@ getChar	KEYWORD2
 getLastChar	KEYWORD2
 loadKeyMap	KEYWORD2
 
+setDebounceThreshold	KEYWORD2
+getDebounceThreshold	KEYWORD2
+
 
 # Instances (KEYWORD2)
 
@@ -25,4 +28,5 @@ I2C_KEYPAD8x8_LIB_VERSION	LITERAL1
 
 I2C_KEYPAD8x8_NOKEY	LITERAL1
 I2C_KEYPAD8x8_FAIL	LITERAL1
+I2C_KEYPAD8x8_THRESHOLD	LITERAL1
 
diff --git a/libraries/I2CKeyPad8x8/library.json b/libraries/I2CKeyPad8x8/library.json
index b190f073..a0de3255 100644
--- a/libraries/I2CKeyPad8x8/library.json
+++ b/libraries/I2CKeyPad8x8/library.json
@@ -1,7 +1,7 @@
 {
   "name": "I2CKeyPad8x8",
   "keywords": "I2C,KeyPad, 8x8, PCF8574",
-  "description": "Arduino library for a KeyPad connected to a PCF8575. 8x8 or smaller.",
+  "description": "Arduino library for a 8x8 (or smaller) keypad connected to an I2C PCF8575.",
   "authors":
   [
     {
@@ -15,7 +15,7 @@
     "type": "git",
     "url": "https://github.com/RobTillaart/I2CKeyPad8x8.git"
   },
-  "version": "0.2.0",
+  "version": "0.3.0",
   "license": "MIT",
   "frameworks": "*",
   "platforms": "*",
diff --git a/libraries/I2CKeyPad8x8/library.properties b/libraries/I2CKeyPad8x8/library.properties
index 59288c9d..98f34056 100644
--- a/libraries/I2CKeyPad8x8/library.properties
+++ b/libraries/I2CKeyPad8x8/library.properties
@@ -1,9 +1,9 @@
 name=I2CKeyPad8x8
-version=0.2.0
+version=0.3.0
 author=Rob Tillaart <rob.tillaart@gmail.com>
 maintainer=Rob Tillaart <rob.tillaart@gmail.com>
-sentence=Arduino library for a KeyPad connected to a PCF8575. 
-paragraph=8x8 or smaller.
+sentence=Arduino library for a 8x8 (or smaller) keypad connected to an I2C PCF8575.
+paragraph=
 category=Signal Input/Output
 url=https://github.com/RobTillaart/I2CKeyPad8x8
 architectures=*
diff --git a/libraries/I2CKeyPad8x8/test/unit_test_001.cpp b/libraries/I2CKeyPad8x8/test/unit_test_001.cpp
index 9142ccc6..cf401761 100644
--- a/libraries/I2CKeyPad8x8/test/unit_test_001.cpp
+++ b/libraries/I2CKeyPad8x8/test/unit_test_001.cpp
@@ -43,6 +43,7 @@ unittest(test_constants)
 {
   assertEqual(64, I2C_KEYPAD8x8_NOKEY);
   assertEqual(65, I2C_KEYPAD8x8_FAIL);
+  assertEqual(255, I2C_KEYPAD8x8_THRESHOLD);
 }
 
 
@@ -59,6 +60,21 @@ unittest(test_constructor)
 }
 
 
+unittest(test_debounce_threshold)
+{
+  const uint8_t KEYPAD_ADDRESS = 0x38;
+  I2CKeyPad8x8 keyPad(KEYPAD_ADDRESS);
+
+  //  default 0
+  assertEqual(0, keyPad.getDebounceThreshold());
+
+  for (uint16_t th = 5000; th < 60000; th += 5000)
+  {
+    keyPad.setDebounceThreshold(th);
+    assertEqual(th, keyPad.getDebounceThreshold());
+  }
+}
+
 
 // unittest(test_KeyMap)
 // {