Approx construction costs:
Part 1 - Fridge-Freezer Door Alarm: US$18
Part 2 - Water Level Detector US$18; Burglar Alarm US$20
Part 3 - Scarecrow US$18; Digital Lock$18
Part 4 - Door Chime US $24; Electronic Dice $20
Part 5 - Kitchen Timer US $24; Room Theremometer US $20
Part 6 - Daily Reminder US $30; Whistle Switch $24
Part 7 - Parking Radar US $30; Telephone Switcher $30
Part 8 - Noughts and Crosses Enigma US $32; Weather Vane Repeater $28

A series of simple, easy-to-build circuits based on one or two CMOS logic chips

It may seem strange, but electronics, like many other fields of human endeavour, is also subject to fashion. As ideas and circuit techniques change, so too do the components available, givingrise to whole series of here today gone tomorrow components.

Every now and then, however, a technique is developed which is so good or has so many advantages that it stands the test of time. The development of the bipolar transistor over 50 years ago was one such example, which effectively spelt the death of the thermionic valve, changing the whole course of electronics design. Bipolar transistors are still widely used today and were the subject of a previous Back to Basics series (Feb to Jun ’03).

Another much quieter, though perhaps no less important revolution, occurred in the early 1970s with the development of CMOS logic devices without which the so called digital revolution, and certainly the personal computer, might probably have remained just an interesting theoretical concept.

CMOS, Complimentary Metal Oxide Semiconductor, to give it its full title, made possible the development of a whole range of very complex integrated circuits containing millions of transistors, ultimately leading to the fabrication of the microcontroller, which was a revolution in its own right and which is so evident in today’s circuit designs.

As well as being used in large scale integrated circuits, CMOS devices are also available in much simpler circuits such as gates and counters. This short series aims to explain briefly the basic operation of CMOS logic circuits, their advantages in the fabrication of complex integrated circuits, and introduce a number of practical applications using just four of the devices from the extensive range available.