The Penguin Tutor: Electronic Circuit and Design

Penguin Tutor, created by Stewart Watkiss, includes projects that can be recreated at home (or by students) by following simple instructions and circuit diagrams that Watkiss has provided. The exercises are based around Arduino software using discrete components. The examples and descriptions on his site focus on the practical side of electronic circuit design, focusing on digital electronics. 

Penguin Tutor includes a brief introduction on circuit design, with twelve projects that can be completed after viewing the introduction. Because the projects are centered around open source tools, they are designed with the Linux user in mind, and require minimal math skills to design a basic circuit.