There was a time when active components such as tubes or transistors were likely to be significantly expensive, and integrated circuits, if they even existed, were out of the reach of most constructors. Making A Transistor Radio, 2nd edition cover. Where once we might have used an op-amp or two, a 555 timer, or a logic gate, it’s ever more common to use a microcontroller or even an IC that though it presents an analog face to the world does all its internal work in the digital domain. When we build an electronic project in 2016, the chances are that the active components will be integrated circuits containing an extremely large amount of functionality in a small space.
