Digital Voltage Output
In this digital circuit example, the potentiometer wiper has been replaced by a single rotary switch which is connected in turn to each junction of the series resistor chain, forming a basic potential divider network. As the switch is rotated from one position (or node) to the next the output voltage, Vout changes quickly in discrete and distinctive voltage levels representing multiples of 1.0 volts on each switching action or step, as shown in the output graph.
So for example, the output voltage will be 2 volts, 3 volts, 5 volts, etc. but NOT 2.5V, 3.1V or 4.6V. Finer output voltage levels could easily be produced by using a multi-positional switch and increasing the number of resistive elements within the potential divider network, therefore increasing the number of discrete switching steps.
Digital Voltage Output Representation
Then we can see that the major difference between an analogue signal or quantity and a digital quantity is that an “Analogue” quantity is continuously changing over time while a “Digital” quantity has discrete (step by step) values. “LOW” to “HIGH” or “HIGH” to “LOW”.
A good example of this would be a light dimmer in your house that varies the lights intensity (brightness) up or down as it is rotated between fully-ON (maximum brightness) and fully-OFF, producing an analogue output that varies continuously. While on the other hand, with a standard wall mounted light switch, the light is either “ON” (HIGH) or it is “OFF” (LOW) when the switch is operated. The result is that there is no in between producing a form of ON-OFF digital output.
Some circuits combine both analogue and digital signals such as an analogue to digital converter (ADC) or a digital to analogue converter (DAC). Either way, the digital input or output signal represents a binary number value equivalent of an analogue signal.
Digital Logic Levels
In all electronic and computer circuits, only two logic levels are allowed to represent a single state. These levels are referred to as a logic 1 or a logic 0, HIGH or LOW, True or False, ON or OFF. Most logic systems use positive logic, in which case a logic “0” is represented by zero volts and a logic “1” is represented by a higher voltage. For example, +5 volts for TTL logic as shown.
Digital Value Representation
| First State | Second State |
| Logic “0” | Logic “1” |
| LOW | HIGH |
| FALSE | TRUE |
| Low Level Voltage Output | High Level Voltage Output |
| 0V or Ground | +5 Volts |
 |  |
Generally the switching from one voltage level, “0” to “1” or “1” to “0” is made as quickly as possible to prevent miss switching of the logic circuit. In standard TTL (transistor-transistor-logic) IC’s there is a pre-defined range of input and output voltage limits for defining what exactly is a logic “1” value and what is a logic “0” value as shown below.
TTL Input & Output Voltage Levels
Then, when using a +5 volt supply any voltage input between 2.0v and 5v is recognised as a logic “1” value and any voltage input of below 0.8v is recognised as a logic “0” value. While the output of a logic gate between 2.7v and 5v represents a logic “1” value and a voltage output below 0.4v represents a logic “0” value. This is called “positive logic” and is used in these digital logic tutorials.
Then binary numbers are commonly used in digital and computer circuits and are represented by either a logic “0” or a logic “1”. Binary numbering systems are best suited to the digital signal coding of binary, as it uses only two digits, one and zero, to form different figures. So in this section about binary numbers we will look at how to convert decimal or base-10 numbers into octal numbers, hexadecimal numbers, and binary numbers.
