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Basic Electronics' theory

The prospect of learning about electronic circuit construction, testing and theory of the equipment they are building daunt many people starting out. Hopefully through a series of articles on this site the beginner will feel more comfortable attempting to build NBTV equipment. Where possible I will include links to other sites offering similar tutorials. NBTV is a hobby in which no 'off the shelf' equipment is available and therefore has to be 'home brewed'. Luckily there are several proven designs around. Many of these have an associated printed circuit board making construction easier and more reliable. Projects without these boards will need to be constructed on breadboard or stripboard, which we will cover later.
Printed circuit board, PCB
To the beginner a printed circuit board populated with various components will seem a maze of multi legged blocks plus strange devices with wires out each end and coloured mass between them. There are many types of components but these normally fall into predefined categories. In order to miniaturise the size of electronic assemblies for the mass market the manufacturer will employ surface mount technology where all the components are soldered directly to the board using a series of 'pads' on each component connection. Larger versions of these devices are still available for the home constructor.
Passive and active
We divide our components into two classes; the first is passive components and the second active. The active class is then sub divided into both analogue and digital. The passive components consist of the following: - Resistors These we can draw an anlogy to a water tap or valve in electronic circuits, they restrict current flow, we can therefore use them to attenuate signals. Resistors are available in different ohmic values and dissipation (watts) as the circuit dictates. Most of our circuits will be using watt resistors and are identified by a series of coloured rings around their bodies denoting their value and accuracy. Resistors are used extensively with other passive components within filter networks where we wish to accept or reject certain frequency signals. When an ac voltage is applied across a resistor there is no phase shift between the applied voltage and the current flowing through the resistor.

As with resistors these devices come in a variety of values and voltages to suit the application. The units used to denote the capacitance is the farad. The capacitors we may use will be between Pico farads to approximately 1000 microfarads. The smaller capacitors are used within filter networks and provide suppression and the larger counterparts are used for 'smoothing' of power supplies. When an ac voltage is applied across a capacitor the current flowing through the capacitor leads the voltage by 90 electrical degrees making this device ideal for filter networks.

Although not used so much nowadays there formally called 'chokes' because they restricted ac current flow in a circuit whilst low resistance to dc. Used mainly in filter circuits either at audio levels or within thyristor circuitry to reduce voltage 'spikes' caused by switching of the thyristor. When an ac voltage is applied across an inductor the current flowing through the capacitor lags the voltage by 90 electrical degrees making this device ideal for filter networks.

The remaining components we are likely to be involved with within NBTV are called semiconductors. These are refered to as active components as unlike their passive counterparts they have the ability to amplify signals. We can break down the semiconductors further to include digital devices such as logic chips, microprocessors, memory devices etc and analogue components including a wide range of amplifiers. The simple transistor is a semiconductor device although many thousand of these devices may be found within a single Integrated circuit package. Please find several sites offering further insight to the world of electronics.

  General electronics

General electronics