Illustrating how transistors can create useful designs. Projects in this issue are a Mini Theremin and a light-sensitive Twilight Switch

This short series presents a number of simple but nonetheless useful gadgets for the beginner to build and use. They could also form the basis of simple designs for GCSE projects.

All require no more than three transistors, which makes them easy to understand and simple to build. Naturally, with so few components, these gadgets cannot hope to match the performance of their commercially built integrated circuit based equivalents. But they all work, and it may even come as a surprise after reading about computer “chips” containing millions of transistors, just what can be achieved with only three.