In electronics and electrical engineering a fuse (from the Latin “fusus” meaning to melt) is a type of sacrificial overcurrent protection device. Its essential component is a metal wire or strip that melts when too much current flows, which interrupts the circuit in which it is connected. Short circuit, overload or device failure is often the reason for excessive current.

A fuse interrupts excessive current (blows) so that further damage by overheating or fire is prevented. Wiring regulations often define a maximum fuse current rating for particular circuits. Overcurrent protection devices are essential in electrical systems to limit threats to human life and property damage. Fuses are selected to allow passage of normal current and of excessive current only for short periods.

A fuse was patented by Thomas Edison in 1890 as part of his successful electric distribution system.

Fuse Operation

A fuse consists of a metal strip or wire fuse element, of small cross-section compared to the circuit conductors, mounted between a pair of electrical terminals, and (usually) enclosed by a non-conducting and non-combustible housing. The fuse is arranged in series to carry all the current passing through the protected circuit. The resistance of the element generates heat due to the current flow. The size and construction of the element is (empirically) determined so that the heat produced for a normal current does not cause the element to attain a high temperature. If too high a current flows, the element rises to a higher temperature and either directly melts, or else melts a soldered joint within the fuse, opening the circuit.

When the metal conductor parts, an electric arc forms between the un-melted ends of the element. The arc grows in length until the voltage required to sustain the arc is higher than the available voltage in the circuit, terminating current flow. In alternating current circuits the current naturally reverses direction on each cycle, greatly enhancing the speed of fuse interruption. In the case of a current-limiting fuse, the arc voltage builds up quickly enough to essentially stop the fault current before the first peak of the ac waveform. This effect significantly limits damage to downstream protected devices.

The fuse element is made of zinc, copper, silver, aluminum, or alloys to provide stable and predictable characteristics. The fuse ideally would carry its rated current indefinitely, and melt quickly on a small excess. The element must not be damaged by minor harmless surges of current, and must not oxidize or change its behavior after possibly years of service.

The fuse elements may be shaped to increase heating effect. In large fuses, current may be divided between multiple strips of metal. A dual-element fuse may contain a metal strip that melts instantly on a short-circuit, and also contain a low-melting solder joint that responds to long-term overload of low values compared to a short-circuit. Fuse elements may be supported by steel or nichrome wires, so that no strain is placed on the element, but a spring may be included to increase the speed of parting of the element fragments.

The fuse element may be surrounded by air, or by materials intended to speed the quenching of the arc. Silica sand or non-conducting liquids may be used.

This operation mode is obtained by a triangular wave generator formed by two op-amps contained in a very cheap 8 pin DIL case IC. Q1 ensures current buffering, in order to obtain a better load drive. R4 and C1 are the timing components: using the values shown in the parts list, the total period is about 4 seconds.

R1,R2 _________4K7 ohm
R3    _________22K ohm
R4    _________2M2 ohm  (See Notes)
R5    _________10K ohm
R6    _________47R ohm  (See Notes)
C1    _________1µF/ 63V Polyester Capacitor
D1    _________5mm. LED (See Notes)
IC1   _________LM358  Low Power Dual Op-amp
Q1    _________BC337  NPN Transistor

Notes:

• The most satisfying results are obtained adopting for R4 a value ranging from 220K to 4M7.
• Adopting for R4 a value below 220K, the pulsing effect will be indistinguishable from a normal blinking effect.
• The LED can be any type and color.
• You can use a filament lamp bulb instead of the LED, provided it is rated in the range 3.2 to 6V, 200mA max.
• Using a bulb as a load, R6 must be omitted.
• Power supply range can be 4 to 6V: 4.5V is the best compromise.
• Do not supply the circuit with voltages exceeding 6V: it will work less good and Q1 could be damaged when a bulb will be used as the load.
• At 6V supply, increase R6 value to 100 Ohm.

Original page of this LED Pulse Effect circuit:
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You can add some resistors in parallel connection for more audio input. To adjust the volume for each input channel, add linear trimmer or potentiometer with configuration: pin1> ground; pin2>output; pin 3>input.

Transistors T1 and T2 (BC548) form a 50Hz multivibrator. For obtaining correct frequency, the values of resistors R3 and R4 may have to be changed after testing. The complementary outputs from collectors of transistors T1 and T2 are given to PNP darlington driver stages formed by transistor pairs T3-T4 and T6-T7 (utilising transistors BD140 and 2N6107).

The outputs from the drivers are fed to transistors T5 and T8 (2N3055) connected for push-pull operation.

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Component list:

R1, R3_________ 1K2 ohm
R2, R4_________ 18 ohm
R5, R6_________ 1 ohm
C1, C2_________ 3u3 50V mini
C3_____________ 22uF 16V
C5_____________ 100uF 35V
C6, C7_________ 220uF 10V
C10, C11_______ 2200uF 35V
C4, C8, C9_____ 100nF
IC_____________ TDA2009A
Heat sink

You can download the 10 Watt Amplifier with TDA2009A in PDF version schematic diagram from HERE

A trimmer or preset is a miniatur adjustable electrical component. It is meant to be ordered aright when installed in whatever device, and never seen or keyed by the device’s user. Trimmers can be potentiometers or varco (variable capacitors – trimmable inductors subsist but are rattling uncommon). They are ordinary in exactitude circuitry similar to  A/V components, and may need to be adjusted when the equipment is serviced. Unlike some another variable controls, trimmers are mounted direct on circuit boards, overturned with a small screwdriver and rated for some less adjustments over their lifetime.

Trimmers become in a difference of sizes and levels of precision; for example, multi-turn cut potentiometers exist, in which it takes individual turns of the fitting propellor to accomplish the modify value, allowing for rattling broad degrees of accuracy.

In 1952, Marlan Bourns patented the world’s prototypal cut potentiometer, trademarked “Trimpot”, a study today commonly consumed to intend to some cut potentiometer.

Voltage is commonly used as a short name for electrical potential difference. Its corresponding SI unit is the volt (not italicized). Electric potential is a hypothetically measurable physical dimension, and is denoted by the algebraic variable V (italicized )

The voltage between two (electron) positions “A” and “B”, inside a solid electrical conductor (or inside two electrically-connected, solid electrical conductors), is denoted by (V_A − V_B). This voltage is the electrical driving force that drives a conventional electric current in the direction A to B. Voltage can be directly measured by an “ideal voltmeter”. Well-constructed, correctly used, real voltmeters approximate very well to ideal voltmeters. For non-scientists, an analogy involving the flow of water is sometimes helpful in understanding the concept of voltage (see below).

Precise modern and historic definitions of voltage exist, but (due to the development of the electron theory of metal conduction in the period 1897 to 1933, and to developments in theoretical surface science from about 1910 to about 1950, particularly the theory of local work function) some older definitions are not now regarded as strictly correct. This is because they neglect the existence of “chemical” effects and surface effects. A particular lesson from surface science is that, to get consistency and universality, formal definitions must relate to positions or (better) electron states inside conductors.

In conduction processes occurring in metals and most other solids, electric currents consist almost exclusively of the flow of electrons in the direction B to A. This movement of electrons is controlled by differences in a so-called “total local thermodynamic potential” often denoted by the symbol µ (”mu”). This parameter is often called the “local Fermi level” or sometimes the “(local) electrochemical potential of an electron” or the “total (local) chemical potential of an electron”. The modern electron-based definition of voltage (V_A − V_B) is in terms of differences in µ:

,

where e is the elementary positive charge. It is sometimes convenient to put µ_B=0 and V_B=0, and choose position “B” so that it can be a convenient reference zero for V. It is common to choose position “B” to be inside a good electrical conductor solidly connected (by a very-low-electrical-resistance path) to the local “Earth” or “Ground”. In the analysis of electrical circuit diagrams, it is common to show the point in the circuit that is being taken as the reference position B, by attaching a “Ground” (”Earth”) symbol to this point.

A common misapprehension is to assume that difference in voltage is always equal to difference in electric potential (i.e. electrostatic potential). This is often untrue, because differences in “chemical effects” (e.g., as between conductors made from different materials) also contribute to differences in µ, and hence to differences in voltage. Some textbooks (especially old physics textbooks) give historic definitions of voltage that are not strictly equivalent to the modern definition. However, the difference in value between a “voltage difference” and the related “electric potential difference” is always small (at most a few volts, often less), and in many contexts it is commonplace (and acceptable) to disregard the distinction. Nonetheless, in some contexts, such as the theory of contact potential differences, the distinction is vital.

Simple applications

Common usage (that “voltage” usually means “voltage difference”) is now resumed. Obviously, when using the term “voltage” in the shorthand sense, one must be clear about the two points between which the voltage is specified or measured. When using a voltmeter to measure voltage difference, one electrical lead of the voltmeter must be connected to the first point, one to the second point.

Voltage between two stated points

A common use of the term “voltage” is in specifying how many volts are dropped across an electrical device (such as a resistor). In this case, the “voltage,” or, more accurately, the “voltage drop across the device,” can usefully be understood as the difference between two measurements. The first measurement uses one electrical lead of the voltmeter on the first terminal of the device, with the other voltmeter lead connected to ground. The second measurement is similar, but with the first voltmeter lead on the second terminal of the device. The voltage drop is the difference between the two readings. In practice, the voltage drop across a device can be measured directly and safely using a voltmeter that is isolated from ground, provided that the maximum voltage capability of the voltmeter is not exceeded.

Two points in an electric circuit that are connected by an “ideal conductor,” that is, a conductor without resistance and not within a changing magnetic field, have a voltage difference of zero. However, other pairs of points may also have a voltage difference of zero. If two such points are connected with a conductor, no current will flow through the connection.

Addition of voltages

Voltage is additive in the following sense: the voltage between A and C is the sum of the voltage between A and B and the voltage between B and C. The various voltages in a circuit can be computed using Kirchhoff’s circuit laws.

When talking about alternating current (AC) there is a difference between instantaneous voltage and average voltage. Instantaneous voltages can be added as for direct current (DC), but average voltages can be meaningfully added only when they apply to signals that all have the same frequency and phase.

Useful formulas

DC (Direct current) circuits

where V = voltage difference (SI unit: volt), I = electric current (SI unit: ampere), R = resistance (SI unit: ohm), P = power (SI unit: watt).

AC (Alternating current) circuits

Where V=voltage, I=current, R=resistance, P=true power, Z=impedance, φ=phase difference between I and V.

AC conversions

Where V_pk=peak voltage, V_ppk=peak-to-peak voltage, V_avg=average voltage over a half-cycle, V_rms=effective (root mean square) voltage, and we assumed a sinusoidal wave of the form V_pksin(ωt − kx), with a period T = 2π / ω, and where the angle brackets (in the root-mean-square equation) denote a time average over an entire period.

Total voltage

Voltage sources and drops in series:

Voltage sources and drops in parallel:

Where is the nth voltage source or drop

Voltage drops

Across a resistor (Resistor R):

Across a capacitor (Capacitor C):

Across an inductor (Inductor L):

Where V=voltage, I=current, R=resistance, X=reactance.

Measuring instruments

A multimeter set to measure voltage.

Instruments for measuring voltage differences include the voltmeter, the potentiometer (measurement device), and the oscilloscope. The voltmeter works by measuring the current through a fixed resistor, which, according to Ohm’s Law, is proportional to the voltage difference across the resistor. The potentiometer works by balancing the unknown voltage against a known voltage in a bridge circuit. The cathode-ray oscilloscope works by amplifying the voltage difference and using it to deflect an electron beam from a straight path, so that the deflection of the beam is proportional to the voltage difference.

Parts List :

Capacitors :
C1, C5 2.2 uF / 50Vecap _________2
C2, C9 10 uF / 25V ecap _________2
C3, C7 100 nF mono (104) ________2
C4 100 uF / 16V ecap ____________1
C6, C8 470 uF / 16V ecap ________2
C10, C11 47 nF mylar (473) ______2

Resistors :
R1, R2 10 ohm ___________________2
Pot 1 10k ohm stereo pot ________1

Misc. :
IC 1, 2 LM386N __________________2
8 pin IC socket _________________2

Download the complete explanation of 1W amplifier circuitHERE

The electronic component, Light Dependent Resistor (LDR) or often called photoresistor or cadmium sulfide (CdS) cell is a resistor whose resistance decreases with increasing incident light intensity. It can also be referenced as a photoconductor.

A Light Dependent Resistor (LDR) is made of a high resistance semiconductor. If light falling on the device is of high enough frequency, photons absorbed by the semiconductor give bound electrons enough energy to jump into the conduction band. The resulting free electron (and its hole partner) conduct electricity, thereby lowering resistance.

A LDR device can be either intrinsic or extrinsic. An intrinsic semiconductor has its own charge carriers and is not an efficient semiconductor, e.g. silicon. In intrinsic devices the only available electrons are in the valence band, and hence the photon must have enough energy to excite the electron across the entire bandgap. Extrinsic devices have impurities, also called dopants, added whose ground state energy is closer to the conduction band; since the electrons do not have as far to jump, lower energy photons (i.e., longer wavelengths and lower frequencies) are sufficient to trigger the device. If a sample of silicon has some of its atoms replaced by phosphorus atoms (impurities), there will be extra electrons available for conduction. This is an example of an extrinsic semiconductor.

Applications

LDR come in many different types. Inexpensive cadmium sulfide cells can be found in many consumer items such as camera light meters, street lights, clock radios, alarms, and outdoor clocks.

They are also used in some dynamic compressors together with a small incandescent lamp or light emitting diode to control gain reduction.

Lead sulfide and indium antimonide LDRs are used for the mid infrared spectral region. Ge:Cu photoconductors are among the best far-infrared detectors available, and are used for infrared astronomy and infrared spectroscopy.
Transducers are used for changing energy types.