The thesis presents a well-structured and practical exploration of integrating the HC-SR04 ultrasonic sensor into a drone system for real-time obstacle detection. The work demonstrates a solid understanding of sensor operation, microcontroller programming, and UAV design principles. The methodology is clearly explained, supported by relevant diagrams and testing results. Overall, the thesis successfully shows how low-cost hardware can be used to enhance drone safety and stability, and it provides a useful foundation for future improvements such as integrating ai or using more expensive sensors. This confirm the reliability and accuracy of the system in detecting obstacles. This study contributes valuable insights for students and researchers interested in low-cost UAV development and embedded sensor applications.