A level :: Design and Technology

A level Objective The challenging task that I have finalised and undertaken for this coursework is to build and test a sensor. I decided to build a sensor, which would automatically change the speed of a fan by using a thermistor. The main objective of the experiment was to monitor and record the voltage change as the temperature changes. Specifically, as predicting that when the temperature increases the voltage would increase and thus the fan speed would increase too, thus causing a cooling effect to the environment. Data Information Thermistors are thermally sensitive resistors and have, according to type, a negative (NTC), or positive (PTC) resistance/temperature coefficient. A thermistor is a type of resistor whose resistance changes significantly when its temperature changes. A negative temperature coefficient thermistor has a resistance that decreases with increase of temperature. This is the most common type. This is the type of resistor that I shall be evaluating and will be using in my experiment. A positive temperature coefficient thermistor has a resistance that increases with increase of temperature. The resistance of a semiconductor generally decreases with increase of temperature. Semiconductors are therefore used to manufacture NTC thermistors. When the temperature of a semiconductor is increased, the number of charge carriers increases as more valence electrons gain sufficient energy to break free from atoms to become conduction electrons. The number of charge carriers increases as the temperature is increased so the resistance of the semiconductor falls. Semiconductors are used to make a wide range of electronic devices including electronic chips, light emitting diodes and solid-state lasers. Communications, commerce and entertainment have been revolutionised as a result of semiconductor devices. In electrical terms, materials are classed as either conductors or insulators or semiconductors. Semiconductors are solid materials with conductivities in between the very high conductivity of metals and the very low conductivities of insulators. There are a variety of types of semiconductor, including metal oxides as well as elements like silicon and germanium. In insulators, essentially all the electrons are tightly bound to atoms or ions, and none are free to move under an external electric field. In effect, these materials do not conduct electricity at all. In metallic conductors, essentially all the atoms are ionised, providing free electrons, which move freely through the ions and can move under an external electric field. These conduction electrons 'glue' the ions together, and provide non-directional bonding which holds the material together. They become shared amongst all the atoms in the material instead of remaining attached to one atom. Semiconductors differ from both insulators and metallic conductors. Only a small proportion of atoms are ionised, so that although there are conduction electrons they are relatively small in number and the