Advances in microprocessor technology and software engineering have resulted in the development of sophisticated robots that are used in modern society as assistive automata for production, security, and farming, among other things. To sustain the development of robots, robotics education should be included in school curricula (i.e., teaching and learning process). However, schools in many developing nations, such as Nigeria, are unable to adapt to this trend due to personnel, technological, infrastructural, and fiscal limitations. To address this problem, a low-cost robotic manipulator arm with real-time control algorithms and a human-robot interface that allows it to be controlled by a microcomputer is developed. This includes its functional model, geometry of link movement, mechanical design, control circuitries, and a Teraterm-based human-robot interface (HRI). Furthermore, an encryption method was developed that maps selected control keys to actuation functions in manipulator chains. We also explored how this robotic manipulator may be used as a teaching tool, particularly for teaching three major industrial technologies: machine-making, electronics, and computing. Our manipulator arm has undergone both unit and system tests and has been used for classroom teaching. Results of its applicability assessment show that our system could aid the teaching of robotics and STEM subjects in schools, as a way to solve the trilemma of harmonizing the concept of machines, electronic control, and computation in multidisciplinary domains.