diff --git a/libraries/LUHN/CHANGELOG.md b/libraries/LUHN/CHANGELOG.md
index f12fbb2e..cdd6a2cc 100644
--- a/libraries/LUHN/CHANGELOG.md
+++ b/libraries/LUHN/CHANGELOG.md
@@ -6,6 +6,19 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/)
 and this project adheres to [Semantic Versioning](http://semver.org/).
 
 
+## [0.2.0] - 2023-05-08
+- add unit test
+- fix stream mode - **add()** and **reset()**
+- fix bugs in generation / validation.
+- add **generateChecksum(const char \* buffer)**
+- change **count** to be 32 bit to support really large streams.
+- add **count()** function to return internal counter.
+- updates readme.md
+- 0.1.x versions are obsolete
+
+
+----
+
 ## [0.1.1] - 2022-12-29
 - add stream interface
   - **char add(char c)**
@@ -14,6 +27,5 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 - update documentation
 - fix warning
 
-
 ## [0.1.0] - 2022-12-24
 - initial version
diff --git a/libraries/LUHN/LUHN.cpp b/libraries/LUHN/LUHN.cpp
index 373a5cf5..9afb2002 100644
--- a/libraries/LUHN/LUHN.cpp
+++ b/libraries/LUHN/LUHN.cpp
@@ -1,7 +1,7 @@
 //
 //    FILE: LUHN.cpp
 //  AUTHOR: Rob Tillaart
-// VERSION: 0.1.1
+// VERSION: 0.2.0
 //    DATE: 2022-12-24
 // PURPOSE: Arduino Library for calculating LUHN checksum.
 //     URL: https://github.com/RobTillaart/LUHN
@@ -12,8 +12,9 @@
 
 LUHN::LUHN()
 {
-  _luhn = 0;
-  _count = 0;
+  _luhnEven = 0;
+  _luhnOdd  = 0;
+  _count    = 0;
 }
 
 
@@ -29,10 +30,11 @@ bool LUHN::isValid(char * buffer)
   uint8_t length = strlen(buffer);
   if (length == 0) return false;
 
+  uint8_t parity = length & 1;
   for (int i = 0; i < length-1; i++)
   {
     uint8_t x = buffer[i] - '0';
-    if (i % 2 == 0) checksum += x;            //  weight 1
+    if (i % 2 != parity) checksum += x;       //  weight 1
     else if (x < 5) checksum += x * 2;        //  weight 2
          else checksum += (x * 2 - 10 + 1);   //  weight 2 + handle overflow.
   }
@@ -42,14 +44,21 @@ bool LUHN::isValid(char * buffer)
 }
 
 
+char LUHN::generateChecksum(const char * buffer)
+{
+  return generateChecksum((char *) buffer);
+}
+
+
 char LUHN::generateChecksum(char * buffer)
 {
   uint16_t checksum = 0;
   uint8_t length = strlen(buffer);
+  uint8_t parity = length & 1;
   for (int i = 0; i < length; i++)
   {
     uint8_t x = buffer[i] - '0';
-    if (i % 2 == 0) checksum += x;            //  weight 1
+    if (i % 2 == parity) checksum += x;       //  weight 1
     else if (x < 5) checksum += x * 2;        //  weight 2
          else checksum += (x * 2 - 10 + 1);   //  weight 2 + handle overflow.
   }
@@ -83,25 +92,44 @@ bool LUHN::generate(char * buffer, uint8_t length, char * prefix)
 }
 
 
+//////////////////////////////////////////////////////////////
+//
+//  STREAM INTERFACE
+//
 char LUHN::add(char c)
 {
+  //  as we do not know the final length in advance 
+  // both parity's must be calculated.
   uint8_t x = c - '0';
-  if (_count % 2 == 0) _luhn += x;
-  else if (x < 5)      _luhn += x * 2;
-  else                 _luhn += (x * 2 - 10 + 1);
-  //  correct
-  if (_luhn > 9)       _luhn -= 10;
+  //  handle even lengths
+  if (_count % 2 == 0) _luhnEven += x;
+  else if (x < 5)      _luhnEven += x * 2;
+  else                 _luhnEven += (x * 2 - 10 + 1);
+  //  handle odd lengths
+  if (_count % 2 == 1) _luhnOdd += x;
+  else if (x < 5)      _luhnOdd += x * 2;
+  else                 _luhnOdd += (x * 2 - 10 + 1);
+  
   _count++;
-  return '0' + (10 - _luhn);
+  if (_count & 1) return '0' + (100 - _luhnOdd) % 10;
+  return '0' + (100 - _luhnEven) % 10;
 }
 
 
 char LUHN::reset()
 {
-  uint8_t last = _luhn;
-  _luhn = 0;
-  _count = 0;
-  return '0' + (10 - last);
+  uint8_t last = _luhnEven;
+  if (_count & 1) last = _luhnOdd;
+  _luhnEven = 0;
+  _luhnOdd  = 0;
+  _count    = 0;
+  return '0' + (100 - last) % 10;
+}
+
+
+uint32_t LUHN::count()
+{
+  return _count;
 }
 
 
@@ -125,5 +153,25 @@ uint8_t LUHN::Marsaglia_mod10()
 }
 
 
+//  EXPERIMENTAL
+//  ~8% faster and 58 bytes bigger (UNO)
+// uint8_t LUHN::Marsaglia_mod10()
+// {
+  // static uint32_t value;
+  // static uint8_t  digits = 0;
+  // if (digits == 0)
+  // {
+    // digits = 4;
+    // m_z = 36969L * (m_z & 65535L) + (m_z >> 16);
+    // m_w = 18000L * (m_w & 65535L) + (m_w >> 16);
+    // value = (m_z ^ m_w);
+  // }
+  // uint8_t rv = value % 10;
+  // value >>= 8;
+  // digits--;
+  // return rv;
+// }
+
+
 //  -- END OF FILE --
 
diff --git a/libraries/LUHN/LUHN.h b/libraries/LUHN/LUHN.h
index d96a965d..f81be8f6 100644
--- a/libraries/LUHN/LUHN.h
+++ b/libraries/LUHN/LUHN.h
@@ -2,7 +2,7 @@
 //
 //    FILE: LUHN.h
 //  AUTHOR: Rob Tillaart
-// VERSION: 0.1.1
+// VERSION: 0.2.0
 //    DATE: 2022-12-24
 // PURPOSE: Arduino Library for calculating LUHN checksum.
 //     URL: https://github.com/RobTillaart/LUHN
@@ -10,7 +10,7 @@
 
 #include "Arduino.h"
 
-#define LUHN_LIB_VERSION                      (F("0.1.1"))
+#define LUHN_LIB_VERSION                      (F("0.2.0"))
 
 
 class LUHN
@@ -22,6 +22,7 @@ public:
   //        buffer == \0 terminated
   bool      isValid(const char * buffer);
   bool      isValid(char * buffer);
+  char      generateChecksum(const char * buffer);
   char      generateChecksum(char * buffer);
 
   //  GENERATE A PRODUCT ID WITH LUHN CHECKSUM
@@ -31,15 +32,16 @@ public:
   //  STREAM INTERFACE
   char      add(char c);
   char      reset();
-
+  uint32_t  count();
 
 protected:
   uint32_t  m_w = 1;  //  random generator parameter
   uint32_t  m_z = 2;  //  random generator parameter
   uint8_t   Marsaglia_mod10();
-  
-  uint8_t   _luhn = 0;
-  uint16_t  _count = 0;
+
+  uint16_t  _luhnEven = 0;
+  uint16_t  _luhnOdd = 0;
+  uint32_t  _count = 0;
 };
 
 
diff --git a/libraries/LUHN/README.md b/libraries/LUHN/README.md
index 4879aeca..7a552180 100644
--- a/libraries/LUHN/README.md
+++ b/libraries/LUHN/README.md
@@ -20,13 +20,28 @@ The LUHN check uses very few resources and is pretty fast.
 
 Basic idea is to put all digits-1 through the formula and the output should equal the last digit.
 
-Note: some LUHN validations uses the reversed product string.
+This LUHN library also includes a "stream" based LUHN calculation, in which digits can be add 
+one at a time (from a stream) and it will return the LUHN checksum so far.
+This is a new application as LUHN depends on the length of the input being odd or even.
+To handle this two values are maintained (for odd and even lengths) and the correct one is returned.
+
+Maintaining two checksums makes the stream **add(c)** algorithm substantial slower (~4x) than 
+the normally used **generateChecksum(buffer)** or the **isValid(buffer)**. 
+However that is a small price for the new functionality.
+
+The amount of data that can be added in stream mode is infinite in theory.
+However that is not tested for obvious reasons, internally a 32 bit counter exists.
+
+
+#### Notes
+
+- some LUHN validations uses the reversed product string.
+- 0.1.x versions are obsolete due to incorrect math.
+
+
+#### Links
 
 - https://en.wikipedia.org/wiki/Luhn_algorithm
-
-
-#### related
-
 - https://github.com/RobTillaart/Adler
 - https://github.com/RobTillaart/CRC
 - https://github.com/RobTillaart/Fletcher
@@ -46,6 +61,7 @@ The parameter buffer is a '\0' terminated char array. Length should be less than
 - **char generateChecksum(char \* buffer)**
 Returns the char '0'..'9' which is the checksum of the code in the parameter buffer.
 The parameter buffer is a '\0' terminated char array. Length should be less than 254.
+- **char generateChecksum(const char \* buffer)** idem.
 - **bool generate(char \* buffer, uint8_t length, char \* prefix)**
 Generates a char array including LUHN number with a defined prefix of max length.
 Returns false if the prefix exceeds length -1.
@@ -53,26 +69,37 @@ Returns false if the prefix exceeds length -1.
 
 #### Stream
 
-- **char add(char c)** add char, return LUHN so far.
+- **char add(char c)** add char, returns LUHN so far.
 - **char reset()** return last LUHN.
+- **uint32_t count()** return internal counter.
+If this value is zero, a new LUHN can be calculated, otherwise call **reset()** first.
+
+The internal counter for the stream interface is 32 bit.
+This limits the number of add() calls to about 4 billion.
+For current implementation the counter is used for even/odd detection,
+and even when it overflows one gets the correct **LUHN**.
 
-The internal counter for the stream interface is 16 bit.
-This limits the nr of add() calls to about 65530.
-(if this is a problem, make it an uinit32_t)
 
 ## Future
 
-#### must
+#### Must
 
-- update documentation
 
-#### should
+#### Should
 
-- unit tests
-- look for optimization
+- look for optimizations
 
-#### could
+#### Could
 
+
+#### Won't (unless)
+
+- create a HEX equivalent of LUHN
+  - LUHN16 ?
+  - easy to enter HEX code with verify / line.
+  - mod N configurable so not only 10 but any N?
+- uint64_t interface for up to 17 digits.
+  - expensive on small processors.
 - uint32_t interface for up to 8 digit ID's (99.999.999)
   - **isValid(uint32_t)**
   - **generateChecksum(uint32_t)**
diff --git a/libraries/LUHN/examples/luhn_check/luhn_check.ino b/libraries/LUHN/examples/luhn_check/luhn_check.ino
index 9c0859f2..ae147c5c 100644
--- a/libraries/LUHN/examples/luhn_check/luhn_check.ino
+++ b/libraries/LUHN/examples/luhn_check/luhn_check.ino
@@ -23,6 +23,8 @@ void setup()
   while (!Serial);
   Serial.println();
   Serial.println(__FILE__);
+  Serial.print("LUHN_LIB_VERSION: ");
+  Serial.println(LUHN_LIB_VERSION);
 
   //  SHOULD PRINT 3
   Serial.println(checker.generateChecksum((char *)"7992739871"));
diff --git a/libraries/LUHN/examples/luhn_check_stream/luhn_check_stream.ino b/libraries/LUHN/examples/luhn_check_stream/luhn_check_stream.ino
index 9ea1c087..38cc072e 100644
--- a/libraries/LUHN/examples/luhn_check_stream/luhn_check_stream.ino
+++ b/libraries/LUHN/examples/luhn_check_stream/luhn_check_stream.ino
@@ -24,8 +24,10 @@ void setup()
   while (!Serial);
   Serial.println();
   Serial.println(__FILE__);
+  Serial.print("LUHN_LIB_VERSION: ");
+  Serial.println(LUHN_LIB_VERSION);
 
-  Serial.println("run I: debug");
+  Serial.println("run I: add() per character");
   for (uint8_t i = 0; i < strlen(ID) - 1; i++)
   {
     c = checker.add(ID[i]);
@@ -46,12 +48,45 @@ void setup()
   }
   c = checker.reset();
   stop = micros();
-  Serial.println();
-  Serial.print("run II:\t");
-  Serial.println(c);     //  should also print 3 .
-  Serial.print("  time:\t");
+  Serial.print("LUHN:\t");
+  Serial.println(c);     //  should print 3.
+  Serial.print("time:\t");
   Serial.print(stop - start);
   Serial.println();
+  Serial.println();
+  delay(10);
+
+  Serial.println("run II: should have same 2nd column as run 1.");
+  for (uint8_t i = 0; i < strlen(ID); i++)
+  {
+    char tmp[32];
+    strcpy(tmp, ID);
+    tmp[i] = 0;
+    c = checker.generateChecksum(tmp);
+    Serial.print(tmp);
+    Serial.print("\t");
+    Serial.println(c);
+  }
+  Serial.println();
+  delay(10);
+
+
+  char tmp[32];
+  strcpy(tmp, ID);
+  tmp[strlen(ID)-1] = 0;
+  start = micros();
+  c = checker.generateChecksum(tmp);
+  stop = micros();
+  Serial.println();
+  Serial.println("run III: generateChecksum()");
+  Serial.print("LUHN:\t");
+  Serial.println(c);     //  should print 3.
+  Serial.print("time:\t");
+  Serial.print(stop - start);
+  Serial.println();
+  Serial.println();
+  delay(10);
+
 
   Serial.println("\ndone...");
 }
diff --git a/libraries/LUHN/examples/luhn_check_stream/output_0.2.0.txt b/libraries/LUHN/examples/luhn_check_stream/output_0.2.0.txt
new file mode 100644
index 00000000..4ed03e6c
--- /dev/null
+++ b/libraries/LUHN/examples/luhn_check_stream/output_0.2.0.txt
@@ -0,0 +1,40 @@
+Arduino UNO
+IDE 1.8.19
+
+luhn_check_stream.ino
+LUHN_LIB_VERSION: 0.2.0
+run I: add() per character
+7	5
+9	4
+9	7
+2	1
+7	0
+3	8
+9	8
+8	2
+7	5
+1	3
+
+LUHN:	3
+time:	256
+
+run II: should have same 2nd column as run 1.
+	0
+7	5
+79	4
+799	7
+7992	1
+79927	0
+799273	8
+7992739	8
+79927398	2
+799273987	5
+7992739871	3
+
+
+run III: generateChecksum()
+LUHN:	3
+time:	64
+
+
+done...
diff --git a/libraries/LUHN/examples/luhn_generate/luhn_generate.ino b/libraries/LUHN/examples/luhn_generate/luhn_generate.ino
index 347180cb..3a713654 100644
--- a/libraries/LUHN/examples/luhn_generate/luhn_generate.ino
+++ b/libraries/LUHN/examples/luhn_generate/luhn_generate.ino
@@ -22,6 +22,10 @@ void setup()
   while (!Serial);
   Serial.println();
   Serial.println(__FILE__);
+  Serial.print("LUHN_LIB_VERSION: ");
+  Serial.println(LUHN_LIB_VERSION);
+  Serial.println();
+  delay(10);
 }
 
 
@@ -35,7 +39,8 @@ void loop()
   Serial.print(checker.isValid(number));
   Serial.print("\t");
   Serial.print(stop - start);
-  //  Serial.print((1.0*(stop - start))/ strlen(number));  per digit
+  Serial.print("\t");
+  Serial.print((1.0 * (stop - start)) / strlen(number));  //  per digit
   Serial.print("\t");
   Serial.println(number);
   delay(100);
diff --git a/libraries/LUHN/keywords.txt b/libraries/LUHN/keywords.txt
index 43b3ccea..4eb757f1 100644
--- a/libraries/LUHN/keywords.txt
+++ b/libraries/LUHN/keywords.txt
@@ -11,6 +11,8 @@ generateChecksum	KEYWORD2
 randomize	KEYWORD2
 generate	KEYWORD2
 
+add	KEYWORD2
+reset	KEYWORD2
 
 # Constants (LITERAL1)
 LUHN_LIB_VERSION	LITERAL1
diff --git a/libraries/LUHN/library.json b/libraries/LUHN/library.json
index 44113262..7a348ef1 100644
--- a/libraries/LUHN/library.json
+++ b/libraries/LUHN/library.json
@@ -15,7 +15,7 @@
     "type": "git",
     "url": "https://github.com/RobTillaart/LUHN.git"
   },
-  "version": "0.1.1",
+  "version": "0.2.0",
   "license": "MIT",
   "frameworks": "arduino",
   "platforms": "*",
diff --git a/libraries/LUHN/library.properties b/libraries/LUHN/library.properties
index e60f5acb..09c42b66 100644
--- a/libraries/LUHN/library.properties
+++ b/libraries/LUHN/library.properties
@@ -1,5 +1,5 @@
 name=LUHN
-version=0.1.1
+version=0.2.0
 author=Rob Tillaart <rob.tillaart@gmail.com>
 maintainer=Rob Tillaart <rob.tillaart@gmail.com>
 sentence=Arduino Library for calculating LUHN checksum.
diff --git a/libraries/LUHN/test/unit_test_001.cpp b/libraries/LUHN/test/unit_test_001.cpp
new file mode 100644
index 00000000..c4b19193
--- /dev/null
+++ b/libraries/LUHN/test/unit_test_001.cpp
@@ -0,0 +1,131 @@
+//
+//    FILE: unit_test_001.cpp
+//  AUTHOR: Rob Tillaart
+//    DATE: 2023-05-02
+// PURPOSE: unit tests for the LUHN checksum
+//          https://github.com/RobTillaart/LUHN
+//          https://github.com/Arduino-CI/arduino_ci/blob/master/REFERENCE.md
+//
+
+// supported assertions
+// ----------------------------
+// assertEqual(expected, actual)
+// assertNotEqual(expected, actual)
+// assertLess(expected, actual)
+// assertMore(expected, actual)
+// assertLessOrEqual(expected, actual)
+// assertMoreOrEqual(expected, actual)
+// assertTrue(actual)
+// assertFalse(actual)
+// assertNull(actual)
+
+
+#include <ArduinoUnitTests.h>
+
+#include "Arduino.h"
+#include "LUHN.h"
+
+
+unittest_setup()
+{
+    fprintf(stderr, "LUHN_LIB_VERSION: %s\n", (char *) LUHN_LIB_VERSION);
+}
+
+unittest_teardown()
+{
+}
+
+
+unittest(test_constructor)
+{
+  LUHN luhn;
+
+  assertEqual('0', luhn.reset());
+  assertEqual('0', luhn.reset());
+}
+
+
+unittest(test_isValid)
+{
+  LUHN luhn;
+
+  assertTrue(luhn.isValid("0"));
+  assertTrue(luhn.isValid("79927398713"));
+  assertTrue(luhn.isValid("1111111"));
+  assertTrue(luhn.isValid("11111111111111111111"));
+
+  //  generated by https://www.dcode.fr/luhn-algorithm
+  assertTrue(luhn.isValid("08192186963920766401"));
+
+
+  // https://www.mobilefish.com/services/credit_card_number_generator/credit_card_number_generator.php
+
+  fprintf(stderr, "Example American Express credit card number\n");
+  //  An American Express credit card number starts with number 34 or 37 and
+  //  the credit card number has total 15 digits:
+  assertTrue(luhn.isValid("377261620324999"));
+  assertTrue(luhn.isValid("349854194206314"));
+
+  fprintf(stderr, "Example Mastercard credit card number\n");
+  //  A Mastercard credit card number starts with number 51, 52, 53, 54 or 55 and
+  //  the credit card number has total 16 digits:
+  assertTrue(luhn.isValid("5181975718047403"));
+  assertTrue(luhn.isValid("5204571199083364"));
+  assertTrue(luhn.isValid("5322683667269933"));
+  assertTrue(luhn.isValid("5477754834149242"));
+  assertTrue(luhn.isValid("5539624233693270"));
+
+  fprintf(stderr, "Example Laser credit card number\n");
+  //  A Laser credit card number starts with number 6304, 6706, 6771 or 6709 and
+  //  the credit card number has total 16, 17, 18 or 19 digits:
+  assertTrue(luhn.isValid("670676038979126821"));
+  assertTrue(luhn.isValid("6771363087405086"));
+  assertTrue(luhn.isValid("6304096514549839"));
+  assertTrue(luhn.isValid("6304219447607087665"));
+}
+
+
+unittest(test_generateChecksum)
+{
+  LUHN luhn;
+
+  assertEqual('3', luhn.generateChecksum("7992739871"));
+}
+
+
+unittest(test_generate)
+{
+  LUHN luhn;
+
+  for (int i = 0; i < 10; i++)
+  {
+    char buffer[24];
+    char prefix[10] = "007";
+    assertTrue(luhn.generate(buffer, 20, prefix));
+    assertTrue(luhn.isValid(buffer));
+    fprintf(stderr, "%d %s\n", i, buffer);
+  }
+}
+
+
+unittest(test_stream)
+{
+  LUHN luhn;
+
+  luhn.reset();
+  char buffer[24] = "7992739871";
+  for (int i = 0; i < strlen(buffer); i++)
+  {
+    char c = luhn.add(buffer[i]);
+    fprintf(stderr, "%d %c\n", i, c);
+  }
+  assertEqual('3', luhn.reset());
+}
+
+
+
+
+unittest_main()
+
+
+//  -- END OF FILE --