The transistor
A transistor is a semiconductor device that, for the purpose of this discussion, functions as a digital switch. A semiconductor is a material that exhibits properties between those of good conductors (like copper wire) and good insulators (like glass or plastic). In a suitable circuit configuration, the conductivity of a semiconductor device can be varied by a control input. A transistor used in this manner becomes a digital switching element.
The transistor switching operation is electrically equivalent to changing between very high and very low resistance based on the state of an input signal. One important feature of switching transistors is that the switching input does not need to be very strong.
This means that a very small current at the switching input can turn on and turn off a much larger current passing through the transistor. A single transistor’s output current can drive many other transistor inputs. This characteristic is vital to the development...