diff --git a/CMakeLists.txt b/CMakeLists.txt
index ee1f43b..4d378df 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -37,4 +37,5 @@ target_sources(${PROJECT_NAME} PRIVATE
     src/main.c
     src/input_handler.c
     src/timer_counter.c
+    src/adc_probe_ext.c
 )
diff --git a/src/adc_probe_ext.c b/src/adc_probe_ext.c
new file mode 100644
index 0000000..2bb6446
--- /dev/null
+++ b/src/adc_probe_ext.c
@@ -0,0 +1,39 @@
+#include <avr/io.h>
+#include "adc_probe_ext.h"
+
+void adc_init(void)
+{
+    // Vcc as reference, select ADC2 (MUX = 0b010)
+    ADMUX = (0 << REFS1) | (0 << REFS0) | // VCC as reference
+            (0 << ADLAR) |                // Right adjust result
+            (0b010);                      // ADC2
+
+    // Enable ADC, prescaler = 64 (assuming 8 MHz → ADC freq = 125 kHz)
+    ADCSRA = (1 << ADEN) |                // Enable ADC
+             (1 << ADPS2) | (1 << ADPS1); // Prescaler = 64
+}
+
+uint16_t adc_read(uint8_t channel)
+{
+    // Set channel (0–7), keeping the other bits in ADMUX
+    ADMUX = (ADMUX & 0xF8) | (channel & 0x07);
+
+    ADCSRA |= (1 << ADSC); // Start conversion
+    while (ADCSRA & (1 << ADSC))
+        ; // Wait for conversion to finish
+
+    return ADC; // Return 10-bit result
+}
+
+uint8_t is_device_connected(void)
+{
+    uint16_t value = adc_read(2); // ADC2 = PA2
+
+    // Zakładamy 5V Vcc → 2.5V = około 512
+    if (value > 400 && value < 600)
+    {
+        return 1; // Podłączone (w granicach tolerancji)
+    }
+
+    return 0; // Odłączone (napięcie bliskie 0 lub 5V)
+}
diff --git a/src/adc_probe_ext.h b/src/adc_probe_ext.h
new file mode 100644
index 0000000..d1e5727
--- /dev/null
+++ b/src/adc_probe_ext.h
@@ -0,0 +1,5 @@
+#pragma once
+
+void adc_init(void);
+uint16_t adc_read(uint8_t channel);
+uint8_t is_device_connected(void);
\ No newline at end of file
diff --git a/src/main.c b/src/main.c
index 3d5e8f4..8ac1620 100644
--- a/src/main.c
+++ b/src/main.c
@@ -5,6 +5,7 @@
 #include "defs.h"
 #include "input_handler.h"
 #include "timer_counter.h"
+#include "adc_probe_ext.h"
 
 void led_pwm(void);
 void probe_int_on(ButtonKey_t *key);
@@ -38,6 +39,7 @@ ButtonKey_t *inputs[2] = {
     &estop_in,
 };
 
+uint8_t ext_divece_connected = 0;
 int main(void)
 {
     LED12_SW_DDR |= (1 << LED12_SW_PIN);
@@ -45,12 +47,13 @@ int main(void)
 
     led_pwm();
     timer0_init();
+    adc_init();
 
     sei(); // Enable global interrupts
 
     while (1)
     {
-
+        ext_divece_connected = is_device_connected();
         for (uint8_t i = 0; i < sizeof(inputs) / sizeof(inputs[0]); i++)
         {
             buttonHandler(inputs[i]);
@@ -74,12 +77,28 @@ void led_pwm(void)
 void probe_int_on(ButtonKey_t *key)
 {
     LED12_SW_PORT |= (1 << LED12_SW_PIN);
-    LED34_SW_PORT &= ~(1 << LED34_SW_PIN);
+    if (ext_divece_connected)
+    {
+        LED34_SW_PORT &= ~(1 << LED34_SW_PIN);
+    }
+    else
+    {
+        LED34_SW_PORT |= (1 << LED34_SW_PIN);
+    }
+    // LED34_SW_PORT &= ~(1 << LED34_SW_PIN);
 }
 void probe_int_off(ButtonKey_t *key)
 {
     LED12_SW_PORT &= ~(1 << LED12_SW_PIN);
-    LED34_SW_PORT |= (1 << LED34_SW_PIN);
+    if (ext_divece_connected)
+    {
+        LED34_SW_PORT |= (1 << LED34_SW_PIN);
+    }
+    else
+    {
+        LED34_SW_PORT &= ~(1 << LED34_SW_PIN);
+    }
+    // LED34_SW_PORT |= (1 << LED34_SW_PIN);
 }
 void estop_on(ButtonKey_t *key)
 {