Wirral & District Amateur Radio Club

Resistor Colour Code


set entirely by the feedback network. They are widely used when a closely controlled amount of gain or some form of signal processing is necessary in an electronic system.

The branch of electronics dealing with devices that generate, transform, transmit, or sense optical, infrared, or ultraviolet radiation, as cathode-ray tubes, electroluminescent and liquid crystal displays, lasers and solar cells.

A light-emitting diode is a semiconductor diode that converts electrical energy into light when an alternating current is applied.
Note: This does not apply to flashing LEDs. Flashing LEDs can be driven from a voltage source, i.e. without a resistor

A liquid crystal display is a screen in which a liquid crystal material

sandwiched between two sheets of glass exhibits computer data when a voltage appears across leads that are connected to character-forming segments etched onto its inner glass surface.

An optocoupler, also known as an optoisolator, is a semiconductor device that allows signals to be transferred between circuits or systems, while keeping those circuits or systems electrically isolated from each other.


Fuses provide reliable and low cost protection against excessive currents, which occur during overloads. There are many different types and styles of fuses and selecting a fuse for a particular application can be difficult.
When replacing a blown fuse, try to obtain a fuse with a rating as close as possible to the original. If it is not possible to locate an exact replacement, remember this a higher current fuse will offer less protection to the equipment, increasing the risk of damage and fire. A lower current fuse will offer more protection, but will be more prone to nuisance blowing. Therefore, it is better to substitute a lower value fuse until the correct type is obtained.

This indicates the current carrying capacity of a fuse under a particular set of test conditions, at 25 o C. Fuses operated at a higher temperature need to be de-rated and allowance must be made for any surge that occurs during switch-on. It is generally recommended that fuses be specified at 125% of normal load current in order to avoid nuisance blowing.

This is the maximum circuit voltage at which a fuse can be relied upon to safely interrupt an over-current. At voltages higher than the rating, a fuse may not be able to suppress the internal arcing that occurs after the fuse link melts. In electronic circuits, where limiting impedances ensure that the fault current is kept low so that a destructive arc cannot occur, fuses may sometimes be used beyond their specified voltage rating.

Standard fast acting fuses are designed to open very quickly during an overload. They are not designed to withstand the inrush current or switch-on surge that occurs in some equipment.
Time delay or slow blow fuses are designed to tolerate the temporary overloads that occur during switch-on, but they still blow quickly if subjected to gross overloads during faults. Slow blow fuses are commonly used in the primary circuits of electronic equipment, where the initial surge can be many times the normal load current. Slow blow fuses and fast acting fuses are not interchangeable due to their different time characteristics.

It should be understood that the overload needed to cause even a fast acting fuse to open quickly must be of the order of 200% or more. An overload of only 35% (ie. a 4A through 3A fuse) could take an hour to open a fuse.


  Reproduced here by kind permission of Click for Maplin website

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