About Digital Communication Methods for Visible Light Communication

The visible light communication (VLC) by LED is one of the important communication methods because LED can work as high speed and VLC sends the information by high flushing LED. We use the pulse wave modulation for the VLC with LED because LED can be controlled easily by the microcontroller, which has the digital output pins. At the pulse wave modulation, deciding the high and low voltage by the middle voltage when the receiving signal level is amplified is equal to deciding it by the threshold voltage without amplification. In this paper, we proposed two methods that adjust the threshold value using counting the slot number and measuring the signal level. The number of signal slots is constant per one symbol when we use Pulse Position Modulation (PPM). If the number of received signal slots per one symbol time is less than the theoretical value, that means the threshold value is higher than the optimal value. If it is more than the theoretical value, that means the threshold value is lower. So, we can adjust the threshold value using the number of received signal slots. At the second proposed method, the average received signal level is not equal to the signal level because there is a ratio between the number of high slots and low slots. So, we can calculate the threshold value from the average received signal level and the slot ratio. Unfortunately, the first proposed method adjusts the threshold value after receiving the data, once the distance between the sender and the receiver is changed, then the performance becomes worse. And after adjusting the threshold, the performance becomes better. Therefore, this method should be used in stable environments. The second proposed method can change the threshold value during the signal is received. That means this method can work very quickly. So, this method can show good performance for the wide range. We show these performances as real experiments.

Arduino Powered GPS Motor Vehicle

This whole study helps us in implementing and making an obstacle avoidance car. This robot is a mobile platform robot that navigates through each and every designated waypoints while trying to avoid any obstruction which comes in the way of the vehicle. We can move the vehicle from one point to another with the help of designated waypoints. This car is based on commonly used RC cars and are made with some modifications and advancements. We can do potential future enhancements by adding a SD card for logging GPS track. We can also add a camera for taking photos and videos. The arduino board acts as a controller which help us to control the speed and change the speed. It also controls the steering of the car to achieve automatic obstacle avoidance. The vehicle’s speed is controlled with the help of pulse wave modulation (PWM) provided to us by the Motor shield. GPS helps us in providing global coordinates of the current location that where the vehicle is present in real time and it also tell us that where that vehicle is heading towards. With the combination of hardware and software we can easily navigate the vehicle and guide it towards right direction..