Abstract: To address the issues of large size, complex wiring, and limited applicability in traditional experimental devices for the Principles of Automatic Control course, a portable, modular, and extensible pocket-sized experimental teaching device has been designed and developed. The device is built around an STM32 microcontroller and adopts a USB Type-C interface to achieve integrated power supply and communication. The base platform and functional modules are connected through pogo-pin interfaces, enabling plug-and-play modular replacement. A companion PC application, developed in C#, supports real-time plotting of response curves and automatic analysis of key performance indices. The compact and lightweight design significantly enhances experimental convenience and flexibility. Pilot teaching results demonstrate that the proposed device effectively improves the quality and efficiency of experimental teaching, showing notable advantages over traditional experimental kits in terms of experimental efficiency, students’ comprehension, teacher–student interaction, and learning extensibility.