This document describes a PC controlled robot that uses a microcontroller, USB to TTL converter, motor driver IC, DC motor, and wheels. The PC sends commands to the microcontroller via USB and UART using X-CTU software. The microcontroller controls the motor driver IC which controls the DC motor direction and movement based on the received commands.

1. PC Controlled ROBOT
This is the robot whose actions are controlled by pressing
predefined keys over PC.
The controlling signals are passed to robot via USB port of PC and
are received at the serial UART port of the microcontroller
mounted on the robot. For this a USB2TTL converter is used and
serial port drivers (X-CTU, TTL driver software) are installed over
PC.
Overview
PC Controlled Robot

2. Hardware components required and their purpose:
1. Microcontroller (ATMega8) development board
2. PC with a free USB port and X-CTU software
3. USB2TTL converter
4. DC motor
5. Motor driver IC (L293D)
6. Wheels
7. Power adopter
 Microcontroller (ATMega8) development board: This is the
brain of this robot in which the program is loaded to do the
required functioning and is interfaced with Bluetooth module
and the motor driver to make the system work as required.
 PC with a free USB port and X-CTU
software: This software is used to
send the commands to robot using PC
over its USB Port in ASCII format.
These commands are defined in the
program burnt into microcontroller.
Commands are first operated by
USB2TTL converter which then
passes the commands in serial form
over the microcontroller’s UART
port.
X-CTU Software

3.  USB2TTL converter: This USB-to-Serial converter module
converts USB signals (3.3 or 5V depending on the jumper
setting) to serial TTL level signals (RX,TX, RTS, CTS, RI,
DTR, DSR and DCD).The TTL signals are available on a
single-row, 0.1" spaced, though-hole solder pads. The TX and
RX signals can also be accessed via a mounted male header.
Please note that this module converts the signals to TTL level
and not to RS232 level.
The intended usage of this module is to directly connect it to
microcontroller’s Rx-Tx lines to interface it with the USB port
of a PC.
USB2TTL Converter
 DC Motor: This motor is controlled with DC voltages and can
move in forward and backward direction according to the
polarity of the voltage applied.
 Motor driver IC (L293D): Microcontrollers can’t supply the
current required by DC motor to run. So, to fulfill this
requirement these motor driver ICs are used.

4. DC motors with Driver IC
 Power adopter: This is used to give appropriate dc power
supply to microcontroller, driver IC sensors and the other
passive components of the robot.
 Wheels: In it three wheels are employed, two at rear end and one
at front end. Rear wheels are attached with the motors and also
control the steering of robot. Front wheel is the loose steered
wheel which moves in the direction of the pressure applied to it.

5. Block Diagram:
PC Controlled Robot
Description
For designing this robot, PC is first made to be equipped with
required software (X-CTU, TTL driver, AVR compiler and
burner). X-CTU sends commands in ASCII format which are
received at UART port of microcontroller.

6. The commands are defined in the program burnt into
microcontroller and on getting the specified command; the
microcontroller sends the appropriate signals to the motor driver
IC which in turn make the motor run in forward or backward
direction or take a turn or to stop.
Programming I/O port of ATMega8:
Each port has three i/o registers associated with it which are
designated as DDRx, PORTx, PINx.
Port Registers in ATMega8

7. DDRx register:
It stands for data direction register. This register is of 8 bits. Value of this
register decides whether the port will act as input port or as output port.
To make any port as input port, the contents of the associated DDRx
register are made 0x00 and to make any port as output port, the contents
of the associated DDRx register are made 0xff.
PORTx register:
This register is responsible for outputting any data to the port. Data to be
outputted to any port is loaded to the corresponding PORTx register after
making the direction of that port as output.
For example:
To send 0x14 to PORTA:-
DDRA=0xFF;
PORTA=0x14;
PINx register:
This register is responsible for inputting data from any port. Data to be
inputted from any port is taken from the corresponding PINx register
after making the direction of that port as input.
For example:
To get data from PORTB:-
DDRA=0x00;
var=PINB; //’var’ is a character type variable