Week 7: September 12 to September 18, 2011

Methodology

The design and development stage of the Micromouse will be divided into two stages beginning with the design and development of hardware and followed by the development of software.

The hardware consists of several sensors as the input to capture data from the environment, a microcontroller as the brain to process the data and sending signals to the output. The output comprises of a few motors which will move the robot accordingly. The development of hardware will be divided into five subsystems: the microcontroller, power supply module, sensors, drive system and chassis.

The block diagram below illustrates the Micromouse operation: 

Microcontroller

The main controller consists of 40-pin Enhanced Flash Microcontroller with operating speed up to 20 MHz clock input. It contains 8192 words of Flash Program Memory, 368 bytes of Data Memory (RAM) and 256 bytes of EEPROM Data Memory. It’s peripheral features comprises of of 5 I/O ports from port A up to port E, 3 types of timer/counter consist of Timer0, Timer1 and Timer2, two capture, compare and PWM modules, Synchronous Serial Port (SSP), Universal Synchronous Asynchronous Receiver Transmitter (USART/SCI), Parallel Slave Port (PSP) and 8 channels of 10-bit Analog-to-Digital Converter (ADC). This microcontroller is an enhanced version from PIC 16F877 which equipped with CMOS Technology which is low power, high speed Flash/EEPROM technology, wide operating voltage range around 2.0V to 5.5V and low power consumption. 

PIC 16F877A from Cytron Technologies

Pin diagram of 40-pin PDIP PIC 16F877A Microcontroller

The PIC 16F877A needs a proper connection to make it alive. Basically, a pull-up resistor is connected to 5V power supply and reset button on the MCLR to enable MCLR function as a reset. A 20 MHz crystal oscillator with 2 capacitors (30 pF) and 5V power supply are needed to ensure that the PIC works successfully.

The function of a microcontroller is to process data received from sensors, calculate a path for the Micromouse to navigate in the maze and control the drive motors to move the Micromouse. The microcontroller board must be low power and the entire board must be smaller than 18 cm x 18 cm. Therefore, for this project, PIC 16F877A was chosen due to its features consist of low-power, high speed Flash/ EEPROM technology with low power consumption which definitely fulfil the requirement. A built-in Analog to Digital Converter (ADC) is an added advantage where the analog input such as data from the sensor can be directly digitize, thus external circuitry for ADC can be eliminated. The IC also has 33 I/O ports which is more than enough to be utilized with the sensors and motors. Below are the special features of PIC 16F877A:

• 100,000 erase/write cycle Enhanced Flash program memory typical 
• 1,000,000 erase/write cycle Data EEPROM memory typical 
• Data EEPROM Retention > 40 years 
• Self-reprogrammable under software control 
• In-Circuit Serial Programming™ (ICSP™) via two pins 
• Single-supply 5V In-Circuit Serial Programming 
• Watchdog Timer (WDT) with its own on-chip RC oscillator for reliable operation 
• Programmable code protection 
• Power saving Sleep mode 
• Selectable oscillator options 
• In-Circuit Debug (ICD) via two pins