Building electronic circuits is one of the most common hands-on activities in learning STEM subjects. Beginning students often find it difficult to translate a circuit schematics into the construction of the physical circuit on a breadboard. In this paper, we describe an Augmented Reality circuit learning software that can provide students with step-by-step instructions by placing virtual circuit components on a physical breadboard. We propose a novel image processing pipeline that can robustly identify the planar structure of a breadboard, even in the presence of occluding circuit components on the breadboard. Using a commercially available library of 3D circuit component models, the estimated 3D structure of the breadboard allows us to render arbitrary circuit components on it in real-time. Experimental results demonstrate that our algorithms are accurate and can produce realistic-looking virtual circuits.