diff --git a/ampel-firmware/co2_sensor.cpp b/ampel-firmware/co2_sensor.cpp
index 9a10a1d1ae82c30a6bd6d6acb108b113fe0ceb91..d28f69bd217befa6fbe18e4ecec383152492c28b 100644
--- a/ampel-firmware/co2_sensor.cpp
+++ b/ampel-firmware/co2_sensor.cpp
@@ -63,7 +63,10 @@ namespace sensor {
     Wire.begin(12, 14); // ESP8266 - D6, D5;
 #endif
 #if defined(ESP32)
+    // For ESP32 : RX on GPIO17, TX on GPIO16
+#   define S8_UART_PORT  2     // Change UART port if it is needed
     Wire.begin(21, 22); // ESP32
+    HardwareSerial S8_serial(S8_UART_PORT);
     /**
      *  SCD30   ESP32
      *  VCC --- 3V3