diff --git a/CMakeLists.txt b/CMakeLists.txt
index ab34fdf..f3caa2c 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -183,7 +183,7 @@ add_subdirectory(lib/fmt EXCLUDE_FROM_ALL)
     endif(NOT CMAKE_EXE_LINKER_FLAGS MATCHES "-fuse-ld=lld")
   endif()
 
-add_executable(fortuna main.cpp generator.cpp generator.h fortuna.cpp fortuna.h accumulator.cpp accumulator.h pool.cpp pool.h event_adder.h event_adder_impl.h)
+add_executable(fortuna main.cpp generator.cpp generator.h fortuna.cpp fortuna.h accumulator.cpp accumulator.h pool.cpp pool.h event_adder.h event_adder_impl.h event_scheduler.h entropy_src.h)
 # ref: https://cmake.org/pipermail/cmake/2016-May/063400.html
 target_link_libraries(fortuna
     PRIVATE cryptopp
diff --git a/entropy_src.h b/entropy_src.h
new file mode 100644
index 0000000..cdfe3ee
--- /dev/null
+++ b/entropy_src.h
@@ -0,0 +1,22 @@
+#ifndef FORTUNA_ENTROPY_SRC_H
+#define FORTUNA_ENTROPY_SRC_H
+
+#include "event_adder_impl.h"
+#include "event_scheduler.h"
+
+namespace fortuna {
+namespace accumulator {
+
+class EntropySrc {
+public:
+	virtual void schedule(accumulator::EventScheduler scheduler) = 0;
+	virtual void event(accumulator::EventAdderImpl adder) = 0;
+
+	EntropySrc(const EntropySrc&) = delete;
+	EntropySrc& operator=(const EntropySrc&) = delete;
+	~EntropySrc() noexcept;
+};
+
+} //namespace accumulator
+} //namespace fortuna
+#endif//FORTUNA_ENTROPY_SRC_H
diff --git a/event_scheduler.h b/event_scheduler.h
new file mode 100644
index 0000000..35a8743
--- /dev/null
+++ b/event_scheduler.h
@@ -0,0 +1,22 @@
+#ifndef FORTUNA_EVENT_SCHEDULER_H
+#define FORTUNA_EVENT_SCHEDULER_H
+
+#include <chrono>
+
+namespace fortuna {
+namespace accumulator {
+
+class EventScheduler {
+public:
+	virtual void schedule(std::chrono::milliseconds delay_ms) = 0;
+
+	EventScheduler(const EventScheduler&) = delete;
+	EventScheduler& operator=(const EventScheduler&) = delete;
+	~EventScheduler() noexcept;
+};
+
+} //namespace accumulator
+} //namespace fortuna
+
+#endif//FORTUNA_EVENT_SCHEDULER_H
+