|Radio and Electronics (DED Philippinen, 66 p.)|
AN INTRODUCTION WHAT FOR?
At first: because the field of electronics is growing very fast. Therefore it is not possible to give an always fitting definition of what ELECTRONICS is.
Secondly: the importance of this field is probably becoming very high - in Tanzania too. So it is necessary to have at least a rough idea of what one is dealing with, if one is studying ELECTRONICS.
In older books you find as an explanation for the term Electronics: Electronics are electric devices in which in some components the electrons are flowing in gases. Components which let the electrons flow in gases, are VALVES.
But even if you have only a very vage idea of the components found nowadays in radios, you know very well, that there are rarely used valves.
Additional you might know too, that radios are only one example of an electronic device.
In all those electronic devices nowadays there are used transistors instead of valves. Transistors are so-called SEMICONDUCTING components. But if all electric devices including semiconducting components would be called electronic devices, the term would be no more helpful.
Because almost each electric device includes this type of components now. During the last decades more and more electric circuits have been invented which had mainly the purpose to control another electric circuit.
To give an example: In a so-called voltage-stabilizer you will find a circuit which would measure the voltage at the input of the stabilizer, and the circuit of the equipment which needs the stabilized voltage. The second circuit will be controlled by the first one, in order to keep the voltage at the sensitive equipment stabile. Controlling in this connection can most simply be: to switch off and on, the lamp, or to dim it. This controlling was done at first by relays or by motoroperated rheostats. The relays and the motor driven rheostats are so-called ELECTROMECHANIC components. In such a component there are always moving parts, and this fact has two main disadvantages:
1. the speed of reaction of these components is rather low (a relays for example is only able to switch off and on 100 times/second)
2. the moving parts are worn out very fast, therefore the service life of those components is rather limited. (relays can be operated only about 1 million times). So it was very important to search for means of controls which do not have those disadvantages.
When the development of radios started it was depending on the development of components like valves, transistors and thyristors. With those new components it was possible now to control circuits:
1. directly without a mechanic interface, and
2. with much higher speed (several million times per second).
So let us agree on the following definition for this script here: CIRCUITS WITHOUT MECHANICAL SWITCHES WHICH ARE DESIGNED TO CONTROL OTHER CIRCUIT SWITH A VERY HIGH SPEED OF REACTION ARE CALLED ELECTRONIC CIRCUITS
Although Electronics started just about eighty years ago. It went through quite some stages within this rather short period. It started in the 20ties of this century, when RADIO TECHNOLOGY was born.
The first challenge was to produce more sound for the listener, and this made it necessary to invent VALVES.
During the 30 ties there was the challenge to handle higher frequencies, and when this goal was achieved, it was possible to think of trials with RADAR and TELEVISION.
In the 40ties the first experiments with so called ELECTRONIC BRAINS (later they were called COMPUTERS) were carried out. At the end of the 40ties - just after the second world war - the SEMICONDUCTORS were more closely researched and led to the inventing of DIODES and TRANSISTORS.
Those new components were very helpful in building much smaller computers which were very important for the first travels to space.
Now the field of application of electronic equipment grew very fast.
On other very important step connected with this field of technology was the change of method to manufacture the circuits:
- while in the first radios the circuit had been WIRED like all the devices
- lateron it was found more economical (because it was much faster and possible with much less faults) to wire it by so called PRINTED CIRCUITS (Insulating boards with copper lines on it, which represent the wires, and which can be printed on the boards)
- the next step was to find a way to engrave whole circuits on a very small piece of semiconducting material. Such circuits were called then INTEGRATED CIRCUITS - they can hold nowadays thousands of transistors.
Basically there are no borders between all fields of electronic devices, as there are:
- communicationsystems (radios, transmitters, recorders etc.)
- data processing systems (computers and measuring instruments)
- controlsystems (in machines, aeroplanes powerstations)
In all those applications the same technical principles and similar basic circuits are applied.
Nevertheless, if one has a general look at all these different kinds of circuits, he will find two different FAMILIES of circuits differentiated according to the method of translating the original physical effect (for example the air pressure of the sound) into an electric signal.
The first family is the so called ANALOGUE CIRCUIT. Here the shape of the output-signal is equal to the input-signal.
The second family is the so-called DIGITAL CIRCUIT. Here the shape of the outputsignal represents the input signal in form of digits(steps). These years the development of electrical technology is very fast. Therefore in future you might easily find circuits of one or the other family which you would have not expected in a special device of a that certain kind.