DIGITAL electronics - logic circuits - 1
V. Ryan © 2003
Most modern electronic devices such as mobile telephones and computers depend on digital electronics. In fact, most electronics about the home and in industry depend on digital electronics to work.
Digital electronics normally based on ‘logic circuits’. These circuits depend on pulses of electricity to make the circuit work. For instance, if current is present - this is represented as ‘1’. If current is not present, this is represented as ‘0’. digital electronics is based on a series of 1s and 0s.
A good example of a digital electronic system is a mobile phone. As you speak into the phone, the digital electronic circuits it contains converts your voice into a series of electronic pulses (or 1s and 0s). These are transmitted and the receiving mobile phone then converts the digital pulses back into your voice. digital circuits are used because they are efficient and work well, also, digital signals are easier to transmit than actual sound (for example a persons voice).
The various parts of a computer communicate through the use of electronic pulses (1s and 0s). Consequently digital logic circuits are ideal for the internal electronics. The main part of the computer is the motherboard. This is a complex piece of electronics that processes all the important data. For instance, when word processing, it is very important to display letters and words on the monitor. The motherboard generates the individual letters on the monitor by sending a series of 1s and 0s to the screen.
When the computer operator presses the letter ‘H’ on the keyboard, the motherboard converts this into a digital signal composed of 1s and 0s. The ‘H’ in the form of 1s and 0s is displayed on the monitor.
When you word-process a paragraph of writing all the letters/words are displayed on the monitor in a similar way. In reality the letters are not composed of 1s and 0s but as black or white pixels.
Digital electronics normally based on ‘logic circuits’. These circuits depend on pulses of electricity to make the circuit work. For instance, if current is present - this is represented as ‘1’. If current is not present, this is represented as ‘0’. digital electronics is based on a series of 1s and 0s.
A good example of a digital electronic system is a mobile phone. As you speak into the phone, the digital electronic circuits it contains converts your voice into a series of electronic pulses (or 1s and 0s). These are transmitted and the receiving mobile phone then converts the digital pulses back into your voice. digital circuits are used because they are efficient and work well, also, digital signals are easier to transmit than actual sound (for example a persons voice).
The various parts of a computer communicate through the use of electronic pulses (1s and 0s). Consequently digital logic circuits are ideal for the internal electronics. The main part of the computer is the motherboard. This is a complex piece of electronics that processes all the important data. For instance, when word processing, it is very important to display letters and words on the monitor. The motherboard generates the individual letters on the monitor by sending a series of 1s and 0s to the screen.
When the computer operator presses the letter ‘H’ on the keyboard, the motherboard converts this into a digital signal composed of 1s and 0s. The ‘H’ in the form of 1s and 0s is displayed on the monitor.
When you word-process a paragraph of writing all the letters/words are displayed on the monitor in a similar way. In reality the letters are not composed of 1s and 0s but as black or white pixels.
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16-04-2009, 11:49 AM
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Digital electronics - logic circuits
V. Ryan © 2003 - 2009
LOGIC
circuits are normally composed of ‘gates’. A combination of gates make
up a circuit and some digital circuits can be extremely complex. It is
the logic gates that produce pulses of electrical current (1s and 0s).
At school level, digital logic circuits are relatively simple. Below
are simple drawings that help explain the two most popular logic gates -
the AND gate and the OR gate.
The simplified AND gate shown above has two inputs, switch A and switch B. The bulb Q will only light if both switches are closed. This will allow current to flow through the bulb, illuminating the filament.
The simplified OR gate shown above has two inputs, switch A and switch B. The bulb Q will light if either switch A or B are closed. This will allow current to flow through the bulb, illuminating the filament.
When the bulb lights this represents a ‘1’
as current is running through the filament. If current is not running
through the filament the bulb will not light and this represents a ‘0’ (zero).
THE ROLE OF TRANSISTORS
Transistors
are vital for digital circuits to work. These components are used as
very fast switches in digital logic circuits. Transistors are normally
so small that hundreds of thousands fit on one processing chip on a
computer motherboard. The types of transistors used in school projects
are normally large enough to fit on the end of a small finger. However,
the way they switched on and off is the same transistor . When a
transistor is switched on it produces a ‘1’ and when it is switched off it produces a ‘0’.
Transistors in the circuit of a computer microprocessor can switch on and off thousands of times per second. Without the invention of the transistor, computer processing power would be very limited and slow.
Two basic examples of simple transistor driven logic (AND / OR) circuits are shown below.
 This is an AND gate circuit and it can be made quite easily. The example shown is built from a modular electronics kit. Both switches ‘A’ and ‘B’ must be pressed together for the bulb to light.If you construct this circuit, you may need to alter the value of the resistors. This will depend on the type of transistors used and whether to bulb or an LED is used. 
This is an OR gate circuit. Either switch ‘A’ or ‘B’ must be pressed for the bulb to
light. The switches do not have to be pressed togeth
Eng.Snsn.Ahmad
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