Velocity measurements using LDR Sensor Khairurrijal Khairurrijal (a,b), Dian Ahmad Hapidin (a), Abas Syahbana (a), Fery Krisnanto (a), Muhamad Zia Pratama Hernawan (a), Muhammad Isro Fiordi (a)
a) Department of Physics, Faculty of Mathematics and Natural Sciences, Institut Teknologi Bandung, Jalan Ganesa 10, Bandung 40132, Indonesia
b) Research Center for Bioscience and Biotechnology, Institut Teknologi Bandung, Jalan Ganesa 10, Bandung 40132, Indonesia
Abstract
Velocity is a physical quantity that is widely used in everyday life. The adverse utilization of the quantity makes the methods and measurement devices are necessary. The most common methods to obtain velocity is by measuring distance traveled by an object in a spesific interval of time. Another way to do this, one could take an advantage from any material that could interact with light in such way there exist a change of physical quantity when the intensity of light modified. This velocity measuring devices work by utilizing the sensor response when an objects pass through it. The commonly used sensors are infrared sensors. By observing the start and end times, at least two such sensors are required in the speed measurement. One sensor that can substitute infrared sensors also rarely used in the velocity measurement is the LDR. LDR is an electric component which its resistance value rises if the intensity of the light on it decreases. This means that the resistance will increase if any object passes through a light-illuminated LDR. In this paper, we discuss velocity measurement using single LDR sensor. To observe the start-finish response, the light sensitive part of LDR sensor will be partially covered (1 x 2.1 cm2), allowing single LDR sensor to detect the velocity of an object. The response of the sensor design will be seen in the graph of the voltage-time graph reading from the bridge circuit and the signal conditioning. In the experiments that performed, the sensor is passed by an objects of different sizes (3.5 x 5.1 cm2 and 3.5 x 0.35 cm2). This size differences produce different outputs. So that the effect of the object size to the device responses can be analyzed. In addition, by placing the cover that unequally divided the LDR light-sensitive part, the object motion direction could be predicted from the time-voltage graph pattern. By applying graph pattern analysis algorithms to the processing unit, the device can be used to measure both speed and motion direction of the object. The resulting output signal depended on the size of the object passing through the sensor, the size of the LDR, and the LDR cover size.
