The leading vehicle senses the path on a given track. Its function is to keep the vehicle itself and the guided vehicle within the boundaries of the track. The track, as shown in figure 2.1, is a 3x3 meter track defined by black boundary lines. The width of this track is 40 cm. In this project, the leading vehicle uses Infrared sensors on a sensor panel to help detect the black lines. It uses an RF antenna to communicate with the guided vehicle, an H-Bridge to run theDC Motors, and a 11 volt battery which provides the power for the vehicle. The figure 3.1 and Table 3.1 describe how the Leading Vehicle shall move under changing conditions.
3.2 CONSTRUCTION OF THE LEADING VEHICLE
Components used for the Leading Vehicle are listed below in table 3.2.
The construction of the leading vehicle is as follows:
•There is a 23 cm metallic sensor panel constructed to give provision for the two IR sensors at the ends of the panel to sense the boundary lines.
• Components were affixed to the chassis with the help of double sided tape. This was done to increase the ease with which the components had to be tested at will rather than using nuts and bolts.
•In order to help the Guided Vehicle sense the Leading Vehicle, a rectangular cardboard was designed and attached at the back acting as the bumper of the vehicle.
• The distance between the motors was fixed by the chassis to be: 4 cm.
• There was no level constructed in order to maintain the balance of the vehicle, and all the four components, namely the Arduino Uno Micro-controller, H-Bridge motor driver, the RF-Antenna and the battery were mounted on the same level.
• The weight was kept to a minimum and was measured to be: 0.740 kg.
• On the sensor panel, provision to keep four IR-Sensors was kept.
• Care was taken to keep the width of the leading vehicle to a minimum.
• The Schematic to the circuit found on the Leading Vehicle is shown in figure 3.2.
3.2.1 Printed Circuit Board Implementation For The Leading Vehicle
To make the design more dynamic, a printed circuit board was designed, fabricated and implemented. Its main purpose was to serve as a power-grid to the leading vehicle and also supply the Arduino Uno with signals from the IR sensors.
Creating a PCB provides a sturdy and reliable backbone for the circuit and gives the project a professional finished quality.
Using PCBs can even help reduce the time spent on building circuits, especially if you are producing multiple units, as you only need to follow a parts placement diagram (there's no longer any need to worry about specific interconnections).
This PCB, after fabrication, was mounted on top of the motors at a level for convenient accessibility to all the required components.
The PCB Design Process
The PCB was designed using Proteus ISIS 7 professional software. These along with EagleEditor are the two mainstream software’s that are used to design printed circuit boards.
The steps in designing the PCB using ISIS professional were:
1. Designing the circuit using Schematic Entry Package (Capture) as shown in figure 3.3.
2. Generating the Netlist for the PCB package.
3. Importing the Netlist into the PCB package (Layout).
4. Placing the components, routing traces, adjusting copper pour and track thickness. Figure 3.4 shows the layout after this step.
5. Generating machining files that contain the plan for the PCB layout that can be etched.
Printing Machining Files
The mirrored image, as shown in Figure 3.5, of the PCB layout was then printed on glossy paper using a Laser Printer. The reason for these choices are explained later (see appendix sub-chapter 6.11 Laser Printer and Glossy Paper) .
Transferring The Image
• First, a single PCB image from the glossy paper was cut out. Next we proceeded with a very clean copper board and a clothes iron. To do so, it was washed with hot water and dish soap. Care was taken to make sure that the copper was dry and that no soap or chemical residue remains as well as to avoid touching the the copper with with fingers as it may keep the toner from sticking.
• The board was then gently rubbed with sand paper. Steel wool was not used as minuscule particles of iron get lodged in the board and eventually rust. When the copper looked clean, shiny and new, this process had concluded and the next step was carried out.
•The PCB mirror image was then placed face down on the copper, ensuring it is correctly positioned. A few pieces of tape were used to secure the glossy paper to the board.
•The hot preheated iron was then placed on top of the paper and copper board. Initial ironing motion is from the center outward towards the sides. On the glossy paper, the back of the paper melts and spreads off the paper to the adjacent portions of the copper board .This helped to to keep the paper in place.
•The entire area of paper was ironed, pressing firmly and staying long enough to ensure the toner melted a bit and binded to the copper. After careful observation it was found that about 10-15 seconds per spot was good and a PCB of this size will take around 1 minute to 90 seconds.
•As the ironing was done, and the paper was subsequently stuck on the board, the board was hot. The board and paper were then immersed in hot water for a few 10 minutes (up to 10 to 20 minutes). This process softened the paper making it easier for it to be gently scratched off.
•Missing toner areas in the board were bolstered, with a line to make the connection, using a permanent black marker.
Etching The Board To remove unwanted copper from the board, the copper board is etched. This process is explained in the appendix (see sub-chapter 6.12 The Etching Process). Finishing The PCB To ensure that the PCB has been fully completed, holes have to be drilled to allow for provisions of the electronic components and making them part of the circuit. A power drill was used to complete this final step of the PCB process, before soldering the components (male headers, DIP switch and 5 volt regulator ) in their respective places. The 5 volt regulator supplies 5 volts to loads connected to its output and 12 volts from the battery goes to its input.