diff --git a/libraries/DAC8554/.arduino-ci.yml b/libraries/DAC8554/.arduino-ci.yml
index ff5659b9..e7cb4633 100644
--- a/libraries/DAC8554/.arduino-ci.yml
+++ b/libraries/DAC8554/.arduino-ci.yml
@@ -2,6 +2,10 @@ compile:
   # Choosing to run compilation tests on 2 different Arduino platforms
   platforms:
     - uno
-    - leonardo
-    - due
-    - zero
+    # - due
+    # - zero
+    # - leonardo
+    - m4
+    - esp32
+    # - esp8266
+    # - mega2560
\ No newline at end of file
diff --git a/libraries/DAC8554/DAC8554.cpp b/libraries/DAC8554/DAC8554.cpp
index 9710223a..286a915a 100644
--- a/libraries/DAC8554/DAC8554.cpp
+++ b/libraries/DAC8554/DAC8554.cpp
@@ -2,7 +2,7 @@
 //    FILE: DAC8554.cpp
 //  AUTHOR: Rob Tillaart
 // PURPOSE: Arduino library for DAC8554 SPI Digital Analog Convertor
-// VERSION: 0.2.3
+// VERSION: 0.2.4
 //     URL: https://github.com/RobTillaart/DAC8554
 //
 //  HISTORY:
@@ -10,11 +10,12 @@
 //  0.1.2   2020-04-06  minor refactor, readme.md
 //  0.1.3   2020-06-07  fix library.json
 //  0.1.4   2020-07-20  fix URL's in demo's; MIT license; minor edits
-//  0.2.0   2020-12-18  add arduino-ci + unit test
+//  0.2.0   2020-12-18  add Arduino-CI + unit test
 //  0.2.1   2021-01-10  fix slave select hardware SPI + getValue() + getPowerDownMode().
 //                      fix unit test.
 //  0.2.2   2021-06-02  compile ESP32
 //  0.2.3   2021-08-29  add support for HSPI / VSPI ESP32 ++
+//  0.2.4   2021-12-15  update library.json, license, unit test, minor edits
 
 
 #include "DAC8554.h"
@@ -34,7 +35,6 @@ DAC8554::DAC8554(uint8_t slaveSelect, uint8_t address)
 }
 
 
-// 0,1,2,4 resp 8550 8551 8552 8554
 DAC8554::DAC8554(uint8_t spiData, uint8_t spiClock, uint8_t slaveSelect, uint8_t address)
 {
   _hwSPI   = false;
@@ -112,8 +112,8 @@ void DAC8554::setGPIOpins(uint8_t clk, uint8_t miso, uint8_t mosi, uint8_t selec
 //
 // SETVALUE
 //
-// channel = 0,1,2,3
-// value = 0..65535
+// channel = 0, 1, 2, 3
+// value   = 0..65535
 void DAC8554::bufferValue(uint8_t channel, uint16_t value)
 {
   uint8_t configRegister = _address;
@@ -134,7 +134,7 @@ void DAC8554::setValue(uint8_t channel, uint16_t value)
 
 
 // channel = 0, 1, 2, 3 depending on type
-// returns 0..65535
+// returns   0..65535
 uint16_t DAC8554::getValue(uint8_t channel)
 {
   return _value[channel];
@@ -155,12 +155,13 @@ void DAC8554::setSingleValue(uint8_t channel, uint16_t value)
 //
 // POWERDOWN
 //
-// channel = 0,1,2,3
+// channel       = 0, 1, 2, 3
 // powerDownMode =
-// DAC8554_POWERDOWN_NORMAL   0x00
-// DAC8554_POWERDOWN_1K       0x40
-// DAC8554_POWERDOWN_100K     0x80
-// DAC8554_POWERDOWN_HIGH_IMP 0xC0
+//   DAC8554_POWERDOWN_NORMAL       0x00
+//   DAC8554_POWERDOWN_1K           0x40
+//   DAC8554_POWERDOWN_100K         0x80
+//   DAC8554_POWERDOWN_HIGH_IMP     0xC0
+//
 void DAC8554::bufferPowerDown(uint8_t channel, uint8_t powerDownMode)
 {
   _register[channel] = powerDownMode;
@@ -278,4 +279,6 @@ void DAC8554::swSPI_transfer(uint8_t value)
   }
 }
 
+
 // -- END OF FILE --
+
diff --git a/libraries/DAC8554/DAC8554.h b/libraries/DAC8554/DAC8554.h
index bf2a075b..8557ca1d 100644
--- a/libraries/DAC8554/DAC8554.h
+++ b/libraries/DAC8554/DAC8554.h
@@ -3,7 +3,7 @@
 //    FILE: DAC8554.h
 //  AUTHOR: Rob Tillaart
 // PURPOSE: Arduino library for DAC8554 SPI Digital Analog Convertor  
-// VERSION: 0.2.3
+// VERSION: 0.2.4
 // HISTORY: See DAC8554.cpp
 //     URL: https://github.com/RobTillaart/DAC8554
 //
@@ -11,13 +11,12 @@
 #include "Arduino.h"
 #include "SPI.h"
 
-#define DAC8554_LIB_VERSION           (F("0.2.3"))
+#define DAC8554_LIB_VERSION                       (F("0.2.4"))
 
-
-#define DAC8554_POWERDOWN_NORMAL     0x00
-#define DAC8554_POWERDOWN_1K         0x40
-#define DAC8554_POWERDOWN_100K       0x80
-#define DAC8554_POWERDOWN_HIGH_IMP   0xC0
+#define DAC8554_POWERDOWN_NORMAL                  0x00
+#define DAC8554_POWERDOWN_1K                      0x40
+#define DAC8554_POWERDOWN_100K                    0x80
+#define DAC8554_POWERDOWN_HIGH_IMP                0xC0
 
 
 class DAC8554
@@ -31,17 +30,20 @@ public:
 
   void     begin();
 
+
   void     bufferValue(uint8_t channel, uint16_t value);
   void     setValue(uint8_t channel, uint16_t value);
   uint16_t getValue(uint8_t channel);
   //writes the value to the channel but does not affect buffered ones
   void     setSingleValue(uint8_t channel, uint16_t value);
 
+
   void     bufferPowerDown(uint8_t channel, uint8_t powerDownMode);
   void     setPowerDown(uint8_t channel, uint8_t powerDownMode);
   uint8_t  getPowerDownMode(uint8_t channel);
   void     setSinglePowerDown(uint8_t channel, uint8_t powerDownMode);
 
+
   // write all buffers to all(up to 4) 8554's channel's
   void     broadcastBuffer();
   // write value to all(up to 4) 8554's channel's
@@ -49,12 +51,15 @@ public:
   // write powerDownMode to all 8554's channel's
   void     broadcastPowerDown(uint8_t powerDownMode);
 
+
   //       speed in Hz
   void     setSPIspeed(uint32_t speed);
   uint32_t getSPIspeed() { return _SPIspeed; };
 
+
   bool     usesHWSPI() { return _hwSPI; };
 
+
   // ESP32 specific
   #if defined(ESP32)
   void     selectHSPI() { _useHSPI = true;  };
@@ -62,6 +67,7 @@ public:
   bool     usesHSPI()   { return _useHSPI;  };
   bool     usesVSPI()   { return !_useHSPI; };
 
+
   // to overrule ESP32 default hardware pins
   void     setGPIOpins(uint8_t clk, uint8_t miso, uint8_t mosi, uint8_t select);
   #endif
@@ -83,6 +89,7 @@ private:
   void     writeDevice(uint8_t configRegister, uint16_t value);
   void     swSPI_transfer(uint8_t value);
 
+
   SPIClass    * mySPI;
   SPISettings _spi_settings;
 
@@ -91,4 +98,6 @@ private:
   #endif
 };
 
+
 // -- END OF FILE --
+
diff --git a/libraries/DAC8554/LICENSE b/libraries/DAC8554/LICENSE
index d29d575f..4231b05c 100644
--- a/libraries/DAC8554/LICENSE
+++ b/libraries/DAC8554/LICENSE
@@ -1,6 +1,6 @@
 MIT License
 
-Copyright (c) 2017-2021 Rob Tillaart
+Copyright (c) 2017-2022 Rob Tillaart
 
 Permission is hereby granted, free of charge, to any person obtaining a copy
 of this software and associated documentation files (the "Software"), to deal
diff --git a/libraries/DAC8554/README.md b/libraries/DAC8554/README.md
index b31f03ec..2a184116 100644
--- a/libraries/DAC8554/README.md
+++ b/libraries/DAC8554/README.md
@@ -7,7 +7,7 @@
 
 # DAC8554
 
-Arduino library for DAC8554 SPI Digital Analog Convertor
+Arduino library for DAC8554 SPI Digital Analog Convertor.
 
 
 ## Description
@@ -23,10 +23,12 @@ The DAC8554 is a SPI based 16 bit DAC with four channels.
 
 - **DAC8554(uint8_t slaveSelect, uint8_t address = 0)** Constructor for hardware SPI,
 since 0.2.0 the slaveSelect pin needs to be defined.
-- **DAC8554(uint8_t spiData, uint8_t spiClock, uint8_t slaveSelect, uint8_t address = 0)** Constructor for the software SPI
+- **DAC8554(uint8_t spiData, uint8_t spiClock, uint8_t slaveSelect, uint8_t address = 0)** 
+Constructor for the software SPI
 - **void begin()** initializes all pins to default state
 - **void setValue(uint8_t channel, uint16_t value)** set the value of the channel to 0 - 65535
-- **void setSingleValue(uint8_t channel, uint16_t value)** writes the value to the channel but does not affect buffered ones. TODO - elaborate.
+- **void setSingleValue(uint8_t channel, uint16_t value)** writes the value to the channel but 
+does not affect buffered ones. TODO - elaborate.
 - **uint16_t getValue(uint8_t channel)** returns the last value written.
 
 
@@ -52,8 +54,9 @@ BEFORE the **begin()** function.
 
 #### experimental
 
-- **void setGPIOpins(uint8_t clk, uint8_t miso, uint8_t mosi, uint8_t select)** overrule GPIO pins of ESP32 for hardware SPI. needs to be called 
-AFTER the **begin()** function.
+- **void setGPIOpins(uint8_t clk, uint8_t miso, uint8_t mosi, uint8_t select)** 
+overrule GPIO pins of ESP32 for hardware SPI. 
+Needs to be called AFTER the **begin()** function.
 
 
 ### Power down
@@ -75,13 +78,9 @@ Check datasheet for details.
 ### Broadcast
 
 - **void bufferValue(uint8_t channel, uint16_t value)** prepare a new value for a channel. 
-- **void broadcastBuffer()** write all buffers to all(up to 4) 8554's channel's
-- **void broadcastValue(uint16_t value)** write value to all(up to 4) 8554's channel's
-- **void broadcastPowerDown(uint8_t powerDownMode)** write powerDownMode to all 8554's channel's
-
-## Future
-
-- testing
+- **void broadcastBuffer()** write all buffers to all(up to 4) 8554's channel's.
+- **void broadcastValue(uint16_t value)** write value to all(up to 4) 8554's channel's.
+- **void broadcastPowerDown(uint8_t powerDownMode)** write powerDownMode to all 8554's channel's.
 
 
 ## Operation
@@ -105,3 +104,8 @@ See examples
 **demo_powerdown.ino**
 - idem
 
+
+## Future
+
+- testing
+
diff --git a/libraries/DAC8554/examples/DAC8554_broadcast/DAC8554_broadcast.ino b/libraries/DAC8554/examples/DAC8554_broadcast/DAC8554_broadcast.ino
index 210e8fb6..759c5a03 100644
--- a/libraries/DAC8554/examples/DAC8554_broadcast/DAC8554_broadcast.ino
+++ b/libraries/DAC8554/examples/DAC8554_broadcast/DAC8554_broadcast.ino
@@ -13,6 +13,7 @@
 DAC8554 DAC_A(10, 0);
 DAC8554 DAC_B(11, 1);
 
+
 void setup()
 {
   Serial.begin(115200);
@@ -57,4 +58,6 @@ void loop()
 {
 }
 
+
 // -- END OF FILE --
+
diff --git a/libraries/DAC8554/examples/DAC8554_hw_spi/DAC8554_hw_spi.ino b/libraries/DAC8554/examples/DAC8554_hw_spi/DAC8554_hw_spi.ino
index 73249e45..080912f3 100644
--- a/libraries/DAC8554/examples/DAC8554_hw_spi/DAC8554_hw_spi.ino
+++ b/libraries/DAC8554/examples/DAC8554_hw_spi/DAC8554_hw_spi.ino
@@ -11,6 +11,7 @@
 
 DAC8554 mydac(10);
 
+
 void setup()
 {
   Serial.begin(115200);
@@ -38,7 +39,7 @@ void loop()
   // minimal sinus
   for (long i = 0; i < 360; i++ )
   {
-    long s = 32768 + 32768 * sin( i * (PI / 180.0));
+    long s = 32767 + 32767 * sin( i * (PI / 180.0));
     mydac.setValue(channel, s);
     int av = analogRead(A0);
     Serial.print(i);
@@ -51,4 +52,6 @@ void loop()
   if (channel >= 4) channel = 0;
 }
 
-// -- END OF FILE --
\ No newline at end of file
+
+// -- END OF FILE --
+
diff --git a/libraries/DAC8554/examples/DAC8554_powerdown/DAC8554_powerdown.ino b/libraries/DAC8554/examples/DAC8554_powerdown/DAC8554_powerdown.ino
index 953cd22e..4e634e70 100644
--- a/libraries/DAC8554/examples/DAC8554_powerdown/DAC8554_powerdown.ino
+++ b/libraries/DAC8554/examples/DAC8554_powerdown/DAC8554_powerdown.ino
@@ -18,6 +18,7 @@ uint8_t chanB = 1;
 uint8_t chanC = 2;
 uint8_t chanD = 3;
 
+
 void setup()
 {
   Serial.begin(115200);
@@ -31,6 +32,7 @@ void setup()
   mydac.setPowerDown(chanD, DAC8554_POWERDOWN_1K);
 }
 
+
 void loop()
 {
   Serial.println("Start sawtooth");
@@ -58,4 +60,6 @@ void loop()
   mydac.setPowerDown(chanA, DAC8554_POWERDOWN_NORMAL);
 }
 
-// END OF FILE
\ No newline at end of file
+
+// -- END OF FILE --
+
diff --git a/libraries/DAC8554/examples/DAC8554_same_time_write/DAC8554_same_time_write.ino b/libraries/DAC8554/examples/DAC8554_same_time_write/DAC8554_same_time_write.ino
index d9804ceb..17ecc636 100644
--- a/libraries/DAC8554/examples/DAC8554_same_time_write/DAC8554_same_time_write.ino
+++ b/libraries/DAC8554/examples/DAC8554_same_time_write/DAC8554_same_time_write.ino
@@ -15,6 +15,7 @@ DAC8554 mydac(10);
 uint32_t lastTime = 0;
 uint16_t state = 0;
 
+
 void setup()
 {
   Serial.begin(115200);
@@ -23,6 +24,7 @@ void setup()
   mydac.begin();
 }
 
+
 void loop()
 {
   uint8_t chanA = 0;
@@ -55,4 +57,6 @@ void loop()
   }
 }
 
-// END OF FILE
\ No newline at end of file
+
+// -- END OF FILE --
+
diff --git a/libraries/DAC8554/examples/DAC8554_sequential_write/DAC8554_sequential_write.ino b/libraries/DAC8554/examples/DAC8554_sequential_write/DAC8554_sequential_write.ino
index 2a7ba11d..b1934363 100644
--- a/libraries/DAC8554/examples/DAC8554_sequential_write/DAC8554_sequential_write.ino
+++ b/libraries/DAC8554/examples/DAC8554_sequential_write/DAC8554_sequential_write.ino
@@ -16,6 +16,7 @@ DAC8554 mydac(10);
 uint32_t lastTime = 0;
 uint16_t state = 0;
 
+
 void setup()
 {
   Serial.begin(115200);
@@ -57,4 +58,6 @@ void loop()
   }
 }
 
-// END OF FILE
\ No newline at end of file
+
+// -- END OF FILE --
+
diff --git a/libraries/DAC8554/examples/DAC8554_sw_spi/DAC8554_sw_spi.ino b/libraries/DAC8554/examples/DAC8554_sw_spi/DAC8554_sw_spi.ino
index c577e40d..28a9e096 100644
--- a/libraries/DAC8554/examples/DAC8554_sw_spi/DAC8554_sw_spi.ino
+++ b/libraries/DAC8554/examples/DAC8554_sw_spi/DAC8554_sw_spi.ino
@@ -51,4 +51,6 @@ void loop()
   }
 }
 
-// END OF FILE
\ No newline at end of file
+
+// -- END OF FILE --
+
diff --git a/libraries/DAC8554/keywords.txt b/libraries/DAC8554/keywords.txt
index a4dc7bc2..e20d4e2a 100644
--- a/libraries/DAC8554/keywords.txt
+++ b/libraries/DAC8554/keywords.txt
@@ -35,6 +35,7 @@ setGPIOpins	KEYWORD2
 
 # Constants (LITERAL1)
 DAC8554_LIB_VERSION	LITERAL1
+
 DAC8554_POWERDOWN_NORMAL	LITERAL1
 DAC8554_POWERDOWN_1K	LITERAL1
 DAC8554_POWERDOWN_100K	LITERAL1
diff --git a/libraries/DAC8554/library.json b/libraries/DAC8554/library.json
index b71a41c5..ad2a1f82 100644
--- a/libraries/DAC8554/library.json
+++ b/libraries/DAC8554/library.json
@@ -15,8 +15,9 @@
     "type": "git",
     "url": "https://github.com/RobTillaart/DAC8554"
   },
-  "version": "0.2.3",
+  "version": "0.2.4",
   "license": "MIT",
   "frameworks": "arduino",
-  "platforms": "*"
+  "platforms": "*",
+  "headers": "DAC8554.h"
 }
diff --git a/libraries/DAC8554/library.properties b/libraries/DAC8554/library.properties
index 1e21a0f6..2251e565 100644
--- a/libraries/DAC8554/library.properties
+++ b/libraries/DAC8554/library.properties
@@ -1,5 +1,5 @@
 name=DAC8554
-version=0.2.3
+version=0.2.4
 author=Rob Tillaart <rob.tillaart@gmail.com>
 maintainer=Rob Tillaart <rob.tillaart@gmail.com>
 sentence=Arduino library for DAC8554 SPI Digital Analog Convertor
diff --git a/libraries/DAC8554/test/unit_test_001.cpp b/libraries/DAC8554/test/unit_test_001.cpp
index 4fdd51d3..bb51abd2 100644
--- a/libraries/DAC8554/test/unit_test_001.cpp
+++ b/libraries/DAC8554/test/unit_test_001.cpp
@@ -30,14 +30,23 @@
 
 unittest_setup()
 {
+  fprintf(stderr, "DAC8554_LIB_VERSION: %s\n", (char *) DAC8554_LIB_VERSION);
 }
 
-
 unittest_teardown()
 {
 }
 
 
+unittest(test_constants)
+{
+  assertEqual(0x00, DAC8554_POWERDOWN_NORMAL  );
+  assertEqual(0x40, DAC8554_POWERDOWN_1K      );
+  assertEqual(0x80, DAC8554_POWERDOWN_100K    );
+  assertEqual(0xC0, DAC8554_POWERDOWN_HIGH_IMP);
+}
+
+
 unittest(test_HW_constructor)
 {
   DAC8554 mydac(10);  // not used address parameter