Undergraduated students in computer science at the University of Brest are learning bases of digital circuits by developing their own functional and structural models. The approach is object oriented to aggregate different abstraction levels in one single structure. This paper presents how simple combinatorial and sequential circuit can be functionally modelized and how complex circuits can hierarchically be built. The students' project consists in designing a logic simulator using Smalltalk environment, which allows them to integrate more easily recent research made in our lab on logic synthesis and on abstract low- level tools for FPGA using the same object oriented approach.