DESIGN AND CONSTRUCTION OF DIGITAL DISTANCE MEASURING INSTRUMENT

ABSTRACT
Distance measurement plays a vital role in engineering, science and business. The distance is always measured between two points. Generally distance measurement is possible only by making contact with the target whose distance is to be measured, but this project discusses the measurement of distance by digital measuring instrument. This is done by providing a circular object (wheel) of about one meter in circumference. Here the distance is calculated by the number of revolution or circulation of the wheel multiplied by the total circumference of the wheel. This device also makes the use of microcontroller for calculating the distance and displaying it on a seven segment display. The digital measuring distance instrument can measure a distance up to 1000 meter. The result obtained from practical distance measurement showed that compared to the use of tape rule, this digital distance measuring instrument is faster and easier. However it has higher error rate since fraction of revolutions are not detected. It is recommended that improvement of the efficiency of this device be made by employing a software that can directly convert number of revolutions to distance.

CHAPTER ONE
INTRODUCTION
1.0         BACKGROUND TO THE STUDY
Taking of measurements has been necessary since human beings first began trading with their neighbors. In addition to trading, early societies also needed to be able to measure to perform many other tasks. When people turned from leading a nomadic life to settling in one place, other measurements such as measurement of land and building materials became important (Crease, 2011). Our knowledge about early measurement comes from historians and archaeologists, leading us to realize that although the roots of many of the early units of measurement were the same, actual values and their application differed from country to country. As our societies become increasingly technology oriented, the quality of measurements has improved over time because of the need for higher measurement accuracy in many fields.
A measuring instrument is a device for measuring a physical quantity. In the physical sciences, quality assurance and engineering, measurement is the activity of obtaining and comparing physical quantities of real-world objects and events (Kirch and Wilhelm,2008). Established standard objects and events are used as units, and the process of measurement gives a number relating the item under study and the referenced unit of measurement (Kirch and Wilhelm, 2008). Measuring instruments, and formal test methods which define the instrument's use, they are the means by which these relations of numbers are obtained. All measuring instruments are subject to varying degrees of instrument error and measurement uncertainty (Creased, 2011).
There are two main types of the measuring instruments: analogue and digital. The analogue instruments indicate the magnitude of the quantity in the form of the pointer movement. One has to learn reading such instruments since there are certain markings on the scale. They usually indicate the values in the whole numbers, though one can get the readings up to one or two decimal places also. The readings taken in decimals places may not always be entirely correct, since some human error is always involved in reading. (B.H. engineers, 2012). The digital measuring instruments indicate the values of the quantity in digital format that is in numbers, which can be read easily. One doesn't needs any prior training to read these instruments since they indicate the values directly in the numerical form. They can give the readings in one or more decimal places. Since there is no human error involved in reading these instruments they are more accurate than the analogue measuring instruments. (B.H. engineers, 2012)
In the construction field, electronic measuring devices are still not widely used due to the high cost of this equipment. Hence there is need to develop designs for accurate measuring device with low cost. Nowadays, measuring distance is considered tedious task in construction field or indoor measuring activities because this task is made by using measuring tape in which at least 2 persons are needed to measure between two distances. Besides, it does not have a perfect accuracy due to parallax and in some cases, presence of some obstacles such as trees hamper linear measurements in the field.
Improvement had been done where some products have infrared light emitters and receivers to determine an object's distance. Other devices have laser-based systems which have improved accuracy and precision. Presently, the detection techniques of laser, radar, and infrared ray have been widely applied in the aspect of obstruction detection and distance measurement. Due to high cost of design and use of laser and radar based measuring instruments, they are not commonly employed. For infrared sensor, the range of the distance that can be measured is very short with only a range of 4-30cm (Crease, 2011). Therefore, a design that can enhance speedy and accurate measurement of distance at low cost is necessary.