People are sensitive to humidity because the skin relies on air to get rid of moisture. When we sweat, water evaporates through the skin and cools us down. If the air is measured to be at 100% relative humidity, it cannot hold any more moisture. Therefore sweat will not be able to evaporate and air will feel warmer than it actually is and our skin will feel extremely sticky causing us to be hot and bothered. However, if the relative humidity is low, sweat will evaporate very quickly and thus our body will stay cool. For example, if the air is 24º and has a relative humidity of 0% , the air will feel to you like it is 21º. If the relative humidity is at 100%, then the temperature will feel like it is 27º. We feel most comfortable when the relative humidity is around 45% (Discovery Communications, 2014).
Due its geographical location (1 degree north of the equator) and maritime exposure, Singapore is characterised by a hot and humid climate. Instead of having clear-cut seasons like summer, spring, autumn and winter, the weather is warm and humid all year round causing the relative humidity to be in the range of 70% - 80%. It varies from 90% in the morning and falls to around 60% in mid-afternoon, when it is not raining. Often the humidity level touches a whooping 100% on rainy days (Janus Corporate Solutions, 2014).
A hygrometer is an equipment used to measure the water vapour in the atmosphere or the relative humidity. They usually rely on measurements of some other quantity such as temperature, pressure, mass or a mechanical or electrical change in a substance as moisture is absorbed. (Wikipedia, 2008) There are a variety of hygrometers such as, simple psychrometers and hair hygrometers or even more complex ones such as a cooled mirror dew point hygrometer. (Kestrel Meters, 2012).
An Arduino, which consists of two parts, the hardware and software, allows users to build close to anything. It is made to be connected to sensors which in turn feed it physical information to act upon. A diversity of sensors can be used, from something as straightforward as pressing a button or something as complicated as using an ultrasound to detect distance between two objects. When there is a change in readings or information, the Arduino will carry out the instructions it is programmed to do. (Charlie, 2008)