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Digital Data

<^< Analogue Data | Course Index | Analogue to Digital Conversion >^>

A digital signal carries its information in the form of a number. Electronic systems use the binary number system, which uses only the numbers 0 and 1, (more of this later.) These two numbers are coded as voltages.

We could decide on the following code: '0' = a low voltage. '1' = a high voltage.

Digital signals then have only two possible voltage values. These are usually the power supply voltages, or as close to them as the system can get, and 0V.

How can we enter these numbers into an electronic system? One (very slow) way would be to use a switch (an example of a digital sensor.) Look at the next circuit diagram:

When the switch is open (not pressed,) the output is pulled down to 0V by the resistor. This output could represent the number '0'. When the switch is closed (pressed,) the output is connected to the positive supply, and so is 5V in this case. This could represent the number '1'. (Note that it would be possible to reverse the positions of the switch and the resistor in the circuit above. In this case pressing the switch would put a logic 0 on the pin.)

The next diagram shows a more complex digital signal.

The binary number represented by the signal is given under the waveform.

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