diff --git a/CMakeLists.txt b/CMakeLists.txt
index cdfabac..666451e 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -1,6 +1,6 @@
 # Generated Cmake Pico project file
 
-cmake_minimum_required(VERSION 3.28)
+cmake_minimum_required(VERSION 3.26)
 
 set(CMAKE_C_STANDARD 11)
 set(CMAKE_CXX_STANDARD 23)
@@ -14,8 +14,8 @@ set(PICO_BOARD pico CACHE STRING "Board type")
 # Pull in Raspberry Pi Pico SDK (must be before project)
 include(pico_sdk_import.cmake)
 
-if (PICO_SDK_VERSION_STRING VERSION_LESS "2.0.0")
-  message(FATAL_ERROR "Raspberry Pi Pico SDK version 2.0.0 (or later) required. Your version is ${PICO_SDK_VERSION_STRING}")
+if (PICO_SDK_VERSION_STRING VERSION_LESS "1.5.0")
+  message(FATAL_ERROR "Raspberry Pi Pico SDK version 1.5.0 (or later) required. Your version is ${PICO_SDK_VERSION_STRING}")
 endif()
 
 project(raspikeyer VERSION "0.0.1" LANGUAGES C CXX ASM)
diff --git a/src/raspikeyer.cpp b/src/raspikeyer.cpp
index cbb36fe..18c9ea4 100644
--- a/src/raspikeyer.cpp
+++ b/src/raspikeyer.cpp
@@ -2,10 +2,10 @@
 #include <stdio.h>
 
 #include <utility>
+#include <functional>
 
 #include "bsp/board.h"
 #include "hardware/adc.h"
-#include "pico/flash.h"
 #include "pico/binary_info/code.h"
 #include "pico/multicore.h"
 #include "pico/stdlib.h"
@@ -102,6 +102,10 @@ void core1_main()
     }
 }
 
+void test() {
+    printf("Test\n");
+}
+
 int main()
 {
     timer_hw->dbgpause = 0; // workaround for problem with debug and sleep_ms
@@ -131,7 +135,10 @@ int main()
     KeyerQueueData keyerQueueData {KeyerQueueCommand::Run, currentWpm, settings.mode, 0};
     queue_add_blocking(&keyerQueue, &keyerQueueData);
 
+    std::function<void()> f_observer = test;
+
     WinKeyer winKeyer;
+    winKeyer.addObserver(f_observer);
 
     pio_hw_t *pio = pio0;
     TM1637 display {DISPLAY_DIO_PIN, DISPLAY_CLK_PIN, pio};
diff --git a/src/settings.cpp b/src/settings.cpp
index 2f8316b..0786140 100644
--- a/src/settings.cpp
+++ b/src/settings.cpp
@@ -1,7 +1,6 @@
 #include <cstring>
 
 #include "pico/stdlib.h"
-#include "pico/flash.h"
 
 #include "settings.h"
 
@@ -67,4 +66,4 @@ Settings read_settings()
     }
 
     return settings;
-}
+}
\ No newline at end of file
diff --git a/src/settings.h b/src/settings.h
index e3a78cf..cd19270 100644
--- a/src/settings.h
+++ b/src/settings.h
@@ -1,6 +1,6 @@
 #pragma once
 
-#include "hardware/flash.h"
+#include "pico/flash.h"
 
 const uint16_t MAGIC_NUMBER = 4;
 
diff --git a/src/winkeyer.cpp b/src/winkeyer.cpp
index c0c53fb..3a35ba3 100644
--- a/src/winkeyer.cpp
+++ b/src/winkeyer.cpp
@@ -103,4 +103,10 @@ void WinKeyer::run(queue_t &queue)
             m_commandState = CommandState::None;
         }
     }
+}
+
+void WinKeyer::addObserver(std::function<void()> obs) {
+    m_observers.push_back(obs);
+
+    obs();
 }
\ No newline at end of file
diff --git a/src/winkeyer.h b/src/winkeyer.h
index e0aabee..19e02c5 100644
--- a/src/winkeyer.h
+++ b/src/winkeyer.h
@@ -1,11 +1,15 @@
 #pragma once
 
+#include <vector>
+#include <functional>
+
 #include "pico/util/queue.h"
 
 class WinKeyer final
 {
   public:
     void run(queue_t &queue);
+    void addObserver(std::function<void()> obs);
 
   private:
     enum class CommandState {
@@ -24,4 +28,5 @@ class WinKeyer final
     CommandState m_commandState {CommandState::None};
     WkMode m_wkMode {WkMode::WK1};
     bool m_hostOpen {false};
+    std::vector<std::function<void()>> m_observers;
 };
\ No newline at end of file