Seven-segment LED displays and Interfacing logic families.

Seven-segment LED displays

Interfacing logic families

Standard digital circuits

Decibel table

The decibel figures are in the centre column: figures to the left represent decibel loss, and those to the right decibel gain. The voltage and current figures are given on the assumption that there is no change in impedance.

Laws

Ampere's Rule Refers to the deflection direction of a magnetic pointer that is influenced by a current; an analogy being that if a person is assumed to be swimming with the current and facing the indicator, the north-seeking pole is deflected towards the left hand, the south pole being deflected in an opposite direction.

Ampere's Theorem The magnetic field from current flowing in a circuit is equivalent to that due to a simple magnetic shell, the outer edge coinciding with the electrical conductor with such strength

that it equals that current strength.

Baur's Constant That voltage necessary to cause a discharge through a determined insulating material! mm thick. The law of dielectric strength is that breakdown voltage necessary to cause a discharge through a substance proportional to a 213 power of its thickness.

Coulomb's Law Implies that the mechanical force between two charged bodies is directly proportionate to the charges and inversely so to the squares of the distance separating them.

Faraday's Laws That of induction is that the e.m.f. induced in a circuit is proportional to the rate of change in the lines of force linking it. That of electrolysis is (1) That the quantity of a substance deposited in defined time is proportional to the current. (2) That different substances and quantities deposited by a single current in a similar time are proportional to the electro-chemical equivalents. The Faraday Effect states that when a light beam passes through a strong magnetic field the plane of polarisation is rotated.

Fleming's Rules By placing the thumb and first two fingers at right-angles respectively. the forefinger can represent the direction of magnetic field; the second finger. current direction; the thumb, motion direction. Use of the right hand in this way represents the relation in a dynamo: use of the left hand represents the relation in a motor.

Hall Effect If an electric current flows across the lines of flux of a magnetic field, an e.m.f. is observed at right-angles to the primary current and to the magnetic field. When a steady current flows in a magnetic field, e.m.f. tendencies develop at rigbt-anlles to the magnetic force and to the current, proponionately to tbe product of the current strength, the magnetie force and the sine of tbe anJie between the direction of quantities.

Joule's Law As a formula this is PRt joules. It refen to that beat developed by the current (I) which is proportional to the square of I

multiplied by Rand t,letting R = resistanee and t =time. Iftbe formula is seen as JH = RPt it equals Elt,lettingJ = joules equivalent of heat, and H = the number of heat units.

Kerr Effect Illustrates that an angle of rotation is proponionai to a magnetisation intensity and applies to the rotation of polarisation plane of plain polarised light as reflected from tbe pole of a magnet. The number (a constant) varies for different wavelengths and materials, making necessary the multiplication of magnetisation intensity in order to find the angle of rotation forming tbe effect.

Lambert's Cosine Law For a surface receiving light obliquely, the illumination is proportional to the cosine of the angle which the light makes with the normal to the surface.

Lenz's Law That induced currents have such a direction that the reaction forces generated have a tendency to oppose the motion or action producing them.

Maxwell's Law (a) Any two circuits carrying current tend so to dispose themselves as to include the largest possible number of lines offorce common to the two. (b) Every electro-magnetic system tends to change its configuration so that the exciting circuit embraces the largest number of lines of force in a positive direction.

Maxwell's Rule Maxwell's unit tubes of electric or magnetic induction are such that a unit pole delivers 411 unit tubes of force.

Miller Circuit A form of circuit in which the time-constant of a resistance-capacitance combination is multiplied by means of the Miller effect on the capacitance. Named after John M. Miller.

MOler Effect Implies that the grid input impedance of a valve with a load in the anode circuit is different from its input impedance with a zero anode load. Should the load in the anode be resistance, the input impedance is purely capacitive. If the load impedance has a reactive component, the input impedance will have a resistive component. In pre-detector amplification, with a.v .c. to signal grids, the capacity across the tuned grid circuits tends to vary with the signal strength, evidencing detuning, the effect causing a charge (electrostatic) to be induced by the anode on the grid.

Planck's Constant Quanta of energy radiated when atomic electrons transfer from one state to another, assuming both to be energy states with electro-magnetic radiation. The constant (h) is given the value of 6·626 x to-34 joule second. his usually coupled to the symbol (v) to represent the frequency of the radiated energy in hertz. That is, the frequency of the radiated energy is determinable by the relation W1 - W2 , this equalling hv. W1 and W2 equal the values of the internal energy of the atom in initial and final stages. This constant is also known as the Quantum Theory.

Sabine's Relation For an auditorium whose boundaries comprise areas A 1, A 2, A 3 •.• etc., of absorption coefficient"'" a2 , a3 ••• etc., the reverberation time, t, is given by

where Vis the auditorium's volume, and l:aA =a 1A 1 +a 1A 1 + ... etc.

Snell's Law For light incident on the boundary between two media, the ratio of the sine of the angle of incidence to the sine of the angle of refraction is a constant; equal to the inverse ratio of the refractive indices of the two media.

Thevenin's Theorem The current through a resistance R connected across any two points A and B of an active network (i.e. a network containing one or more sources of e.m.f.) is obtained by dividing the p.d. between A and B, with R disconnected, by (R+r), where r is the resistance of the network measured between points A and B with R disconnected and the sources of e.m.f. replaced by their internal resistances.

CCITT recommendations

Connectors and connections

Data interchange by modems

When transmitting and receiving data across telephone or other circuits, the equipment which actually generates and uses the data (e.g., a computer or VDU terminal) is known as data terminating equipment (DTE). The equipment which terminates the telephone line and converts the basic data signals into signals which can be transmitted is known as data circuit-terminating equipment (DCE). As far as the user is concerned the interface between DTE and DCE is the most important. CCITT recommendation V24 defines the signal interchanges and functions between DTE and DCE; these are commonly known as the 100 series intercnange circuits:

Modem connector pin numbers

The connectors used with 100 series interchange circuits and its pin assignments are defined by international standard ISO 2110 and are (for modems following the CCITT recommendations V21, V23, V26, V26bis, V27 and V27bis) as follows:

Automatic calling

A similar series of interchange circuits is defined in CCITT recommendation V25 for automatic calling answering between modems over the telephone network. This is the 200 series interchange circuits:

RS   232C

The EIA equivalent of CCITT V24 interface is the RS 232C specification, which similarly defines the electrical interface between DTE and DCE. Although the two have different designations, they are to all practical purposes equivalent. The RS 232C interchange circuits are:

RS449

The EIA RS 232C standard, although the most common, is by no means perfect. One of its main limitations is the maximum data rate 18·2 Kbaud. Various improved interchange circuits (RS 422, RS 423) have been developed. The RS 449 standard is capable of very fast data rates (up to 2 Mbaud):

Centronics interface

Most personal computers use the Centronics parallel data transfer to a printer. The pin connections of the connector, abbreviations and signal descriptions are shown.

All signals are standard TTL, although not all signals necessarily exist in any given interface.

Audio connedors

The DIN standards devised by the German Industrial Standards Board are widely used for the connection of audio equipment. The connectors arc shown below. The 3-way and 5-way 45 are the most common, and connections for those are listed.

Coaxial connectors

A number of connectors are available for use with coaxial cables.
The most common are:

Videorecorder (televisions/camera connectors

Standard pin configurations for video recorders, televisions and video cameras are shown below. Many follow standard DIN connector pinouts, but video camera and SCART connectors differ significantly.

SCART (BS 6552)

SCART connectors, also known as Peri television or Euroconnector connectors, feature two control systems which allow remote control over the television's or videorecorder's functions.

The simplest is a source switching input (pin 8) in which an external source (videorecorder, computer, etc.) can, by issuing a 12 volt signal, cause the television to switch to baseband inputs.

A more complex control system, called domestic data bus (D2 B), is given through pins 10 and 12, in which serial data can be passed between controlling microprocessors in the television and external equipment. No standard yet exists for D2 B.