diff --git a/platformio.ini b/platformio.ini
index 96febe7..33c978d 100644
--- a/platformio.ini
+++ b/platformio.ini
@@ -12,3 +12,11 @@
 platform = atmelavr
 board = nanoatmega328
 framework = arduino
+build_src_filter =
+    +<*>
+    -<.git/>
+    -<.svn/>
+    -<blink/>
+    -<button_interrupt/>
+    -<button_poll/>
+    -<trafficlight/>
\ No newline at end of file
diff --git a/src/button_poll/button.cpp b/src/button_poll/button.cpp
index 11d89d7..207a857 100644
--- a/src/button_poll/button.cpp
+++ b/src/button_poll/button.cpp
@@ -10,8 +10,6 @@
 // PORTx set bit of port value
 // PINx read voltage of bit of port D
 
-#ifdef BUTTON_POLL
-
 void init() {
     // ---------------------------------------
     // set Port B to output
@@ -43,5 +41,3 @@ void loop() {
         CLR_BIT(PORTB, DDB5);
     }
 }
-
-#endif
\ No newline at end of file
diff --git a/src/main.cpp b/src/main.cpp
index c8538da..e7eb02c 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -5,12 +5,8 @@ extern void loop();
 //#include "blink/blink.h"
 //#include "button_poll/button.h"
 //#include "button_interupt/button.h"
-#include "trafficlight/trafficlight.h"
-
-//#define BLINK
-//#define BUTTON_POLL
-//#define BUTTON_INTERRUPT
-#define TRAFFIC_LIGHT
+//#include "trafficlight/trafficlight.h"
+#include "summer/summer.h"
 
 int main() {
     init();
diff --git a/src/summer/summer.cpp b/src/summer/summer.cpp
new file mode 100644
index 0000000..12e18a7
--- /dev/null
+++ b/src/summer/summer.cpp
@@ -0,0 +1,29 @@
+//
+// Created by servostar on 30.10.23.
+//
+
+#include "summer.h"
+
+ISR (TIMER0_COMPA_vect)
+{
+    PORTB = ~PORTB;
+}
+
+void init() {
+    DDRB = 255;
+    PORTB = 0;
+
+    TCCR0A |= (1 << WGM01);   // set timer to CTC
+
+    OCR0A = 0x70; // count up to this value
+
+    TIMSK0 |= (1 << OCIE0A);  // enable timer 0
+
+    sei();  // enable interrupts
+
+    TCCR0B |= (1 << CS02);    // start timer and set prescaler to 256
+}
+
+void loop() {
+
+}
diff --git a/src/summer/summer.h b/src/summer/summer.h
new file mode 100644
index 0000000..4d2f081
--- /dev/null
+++ b/src/summer/summer.h
@@ -0,0 +1,13 @@
+//
+// Created by servostar on 30.10.23.
+//
+
+#ifndef ARDUINO_SUMMER_H
+#define ARDUINO_SUMMER_H
+
+#include "prelude.h"
+
+void init();
+void loop();
+
+#endif //ARDUINO_SUMMER_H
diff --git a/src/trafficlight/trafficlight.cpp b/src/trafficlight/trafficlight.cpp
index a170f4d..415ea66 100644
--- a/src/trafficlight/trafficlight.cpp
+++ b/src/trafficlight/trafficlight.cpp
@@ -4,8 +4,6 @@
 
 #include "trafficlight.h"
 
-#ifdef TRAFFIC_LIGHT
-
 void init() {
     // set Port B bit 0,1,2 to output mode
     DDRB = 0b00000111;
@@ -31,4 +29,3 @@ void loop() {
     // set to red
     PORTB ^= 0b00000110;
 }
-#endif
\ No newline at end of file