This guide aims to provide the reader with a collection of practical working circuits, together with supporting information so that circuits can be produced in the shortest possible time, and without recourse to theoretical texts. All circuits described have been thoroughly tested and, as far as possible, a range of commonly available low-cost components has been adopted. Information has been included so that the circuits can readily be modified and extended by readers to meet their own individual needs. Related circuits have been grouped together and cross-referenced within the text so that readers are aware of which circuits can be readily connected together to form more complex systems. As far as possible, a common range of supply voltages, signal levels and impedances has been utilized.