In this paper we present activities that can help students deepen their understanding of DC circuits and develop practical competences. The students investigate electric properties of commercially available conductive thread and solve a practical design task using the thread. The activities follow the framework of investigative science learning environment (ISLE)--an approach to learning and teaching that helps students learn fundamental physics concepts by engaging them in processes that mirror those used by physicists when they develop new knowledge and use it for practical applications. In this paper this framework is extended to engineering.