WEEK 6

Date:  21- 25 October 2013

Subject : 1) Research about the components used in Smart Grass Cutter technology.
            

Introduction:

The purpose of this task is to do a research about each components that will be used in this project and sketch a block diagram to show the Input, Process and Output for Smart Grass Cutter.

Objectives: 

1. To find the suitable component that will need used in this projects.

Project Description:

Information is gathered using resources such as the internet, the books and journals available in the library. Supporting components in this case means components such as resistors, capacitors, inductors and amplifiers. Information on these components can be obtained easily from normal component stores and website. One thing to be remembered is the fact that each component picked must match in the system as so to balance it and not disrupt the inner workings of the project.

1.  PIC Microcontroller

• PIC16F877A-I/P microcontroller is used to control the whole system. It is designed using flash technology. So the PIC can read/write program for more than 100,000 times. The PIC can operate using 4.5V to 6.0V DC voltage. In the project is operating at 5.0V (by using 7805). It is DIP layout (dual in line package) and suitable for student project. It has 40 pins but only 33 I/O pins can be set as digital input or digital output. 

• The digital output of the PIC is 5V (for signal 1) and 0V (for signal 0) these signals will be directly connected to actuators for control purpose. When the PIC pin is set as digital input. It will detect input voltage 5V as signal 1 and 0V as signal 0. Any voltage less than 0V or more than 5V will damage PIC. Based on Figure 1, it is the features that have in PIC 16F877.

Figure 1: Key Features for PIC

Figure 2: PIC Diagram

Based on figure 2, it can see that the PIC have 5 port which is can connected with the input or output part. I can used this PIC for the brain for this project. The program will burn on that PIC to controlled the robot. 

2.  Voltage Regulator Module/Power Supply

Figure 3: Power Supply Circuit

The voltage regulator module is used to protect PIC and other connected sensors / actuators from over voltage. This is because PIC and all other connected sensors, actuators all support 5V DC only. Over voltage will cause any of the module burn.

• LM7805 is used to regulate voltage in the system and output 5V DC (max output current: 1000mA). It supports input voltage from 7V DC to 18V DC. If the input voltage is over, the LM7805 will burn or auto shutdown due to overheat.

•  The generated 5V from LM7805 will be noise filtered by 0.1uF ceramic capacitor and a 1000uF electrolytic capacitor. This is to avoid high frequency oscillation on the outputs which may cause system hang or unstable.

•  A diode is connected at the input of the LM7805. This is to avoid voltage connected reversely.

•  An on/off switch is used to turn on/off the system and a LED (5V, 5mA) is used to indicate the system is power on/off. The LED is connected through 1KR resistor to limit current pass through LED is 5mA.
 

 

3.  Infrared Sensor (GP2D12)

The GP2D12 is an analog infrared proximity sensor. It can be used to detect obstacles. This sensor has a LED that emits infrared light. Infrared light has the interesting property that it bounces on obstacles. On the front of the sensor, beside the LED that emits the infrared, there is a photo diode that is sensible to infrared light. It will vary the output voltage based on the amount of infrared light that bounces back to the sensor. The sensor can measure in the range from 10-80 cm. The voltage is approximately 2.4V at 10cm and at 0.52 at 60cm. The sensor draws about 34mA. The maximum is stated to be 50mA.
 

Figure 4: Infrared Sensor Type GP2D12

 

Figure 5: IR Sensor Range Detector

 4. Motor Drive

Motors are high-powered devices in the world of digital electronics. A typical digital output can supply about 10 to 20 milliampere (mA) of current, a small permanent-magnet motor requires anywhere from 500 to 4000 mA of current. Special  circuits are therefore required to drive motors. For this project it must need 3 DC motor drive. It's use 2 motors which is for forward and reverse direction while another motor is for blade cutter. 

       In my research, to make the DC motor become two different direction it must need another component which is transistor.

         A circuit known as the H-bridge (named for its topological similarity to the letter "H") is commonly used to drive motors. In this circuit (depicted in Figure 6), two of four transistors are selectively enabled to control current flow through a motor.

 

Figure 6: The H Bridge Circuit

 

Figure 7: The H-Bridge with Left-to-Right Current Flow

As shown in Figure 7, an opposite pair of transistors (Transistor One and Transistor Three) is enabled, allowing current to flow through the motor. The other pair is disabled, and can be thought of as out of the circuit. By determining which pair of transistors is enabled, current can be made to flow in either of the two directions through the motor. Because permanent-magnet motors reverse their direction of turn when the current flow is reversed, this circuit allows bidirectional control of the motor.

Problem Encountered:

From this research, I have found an idea about the component that I should use in this project. Therefore more research in website or going to Jalan Pudu to find the suitable types of components for Smart Grass Cutter. There have some problems regarding the component such as gearing system and also program that act as a brain to the robot. However the project is still on schedule and will proceed as how the project was planned.

Project Outcome:

More outcome has achieved from this research. Next planning is want to research about types of motor used, relay, gearing system and the design for Smart Grass Cutter. One of my idea is I will used DC motor and some mechanical part and also gearing system to make the robot move. My research project is on schedule and I should encounter no problems finishing it.