A new teaching method under the name of STEM, integrating the disciplines of Science, Technology, Engineering, and Mathematics, is now taught by teachers in their classes. Considering that the generation that grows up in the 21st-century has grown up with technology, it is thought that integrating technology into lessons helps students learn the subject. The study aims to develop five STEM activities for the human body systems lesson by integrating the coding-based Arduino into STEM education. The activities were implemented to 6th-grade students for seven weeks and the effects on students' skills of establishing a cause-effect relationship. The study method was pre-test-post-test quasi-experimental design, and the cause-effect relationship scale was used as a data collection tool. As a result of the study, a significant difference was found between the Arduino-supported STEM activities developed and the students' skills of establishing a cause-effect relationship.