Download A Mobile Robot

A Mobile Robot
THE ROBOT CIRCUITS
The mobile robot consists of two units. The first one is the interface & control
unit and the other one the robot itself.
The interface and control unit is plugged directly to the Centronic port of the
computer and manages the interfacing between the computer and the robot,
and controls the movements, the sounds and lights of the robot.
The robot has two drive wheels which are independently controlled by two
motors. Lights and sounder are installed on the board to give simple light and
sound effects. The robot and the interface & control unit are connected by a
transmission cable.
The circuit diagram of the interface & control unit is shown below:
and the the circuit on the robot consisting of motors, lights and sounders is as
follows:
The interface unit is connected to the PC's Centronic port via five wires, four of
which are data lines and the other one is the ground.
Each of the four lines has a dedicated function. The first line (P1: POWER
ON/OFF) controls the ON or OFF of the power supply to the motors. A logic 1
on the line will supply the power to the motors. A logic 0 will switch off the
power. The second (P2: MOTOR-1) and third (P3: MOTOR-2) lines control the
directions of the motors. A logic 1 on the lines will make the motor to turn
clockwise and a logic low will make the motor to turn anti-clockwise. The two
lines are therefore used for controlling the movements of the robot. The forth
line (P4: SOUNDER) controls the sounder on the robot. These four lines are
connected to Pin 2 through Pin 5 of the 25-pin D-type male connector which is
plugged into the Centronic port of the computer.
Those four data lines are fed into IC, an opto-isolator. The data lines are
connected to the Light Emitting Diodes inside IC1. Resistors R1 through R4 are
resistors for limiting the electric current passing through these LEDs. When a
line is in logic low, (note: a logic low corresponds to a voltage swing from 0V to
0.8V. It is often referred to as '0'). the LEDs will not be lit and subsequently the
photo-transistor is turned off. When the line is in logic high (i.e. a voltage swing
from 2V DC to 5V DC. It is often referred to as '1'). The LED will be lit and turn
on the corresponding photo-transistor. An opto-isolator provides electric
isolation between two sides and the maximum isolation voltage is well over
4000V. Using such a device in the circuit ensures that in case of any circuit
malfunction on the robot side, your computer is always safe.
MOTOR POWER ON/OFF
The POWER ON/OFF line controls the on/off via the first opto-transistor switch.
When the line is high, the emitter of the photo-transistor goes high. The emitter
signal is feed to a transistor switch based on TR1. The control signal is fed to
the base of the transistor via a resistor R5. The 12V DC power supply is
connected to the collector of the transistor and the controlled voltage is from the
emitter of the transistor. When the base is in high state. the transistor is turned
on. It just behaves like an ordinary switch which makes the 12V DC power
supply to appear on the emitter. On the other hand if the base control signal is
in low state, the transistor is turned off. The controlled DC power supply from
the emitter of the transistor is fed into a voltage regulator IC, 7805 which
converts the 12V DC into a stable 5V DC power supply. This 5V power supply is
then used for driving the two motors which are connected in series. R6 is a
small resistor connected in series with the motors for limiting the current through
the 7805 in case of short circuit in the transmission cable or on the circuit board
on the robot.
DIRECTION OF MOTORS
The turning directions of the motor are controlled by a DTDP relay. In the circuit,
the second and third data lines from the Centronic port control the On/Off via
the 2nd and 3rd opto-transistors, which in turn controls whether the relays are
energized or not. When the relay changes its status, the polarity of the power
supply to the motor is changed thus reversing the turning direction of the motor.
D1 and D2 are diodes which are connected in parallel to the coils of the relays
to protect the opto-isolators, since when the relay is de-energized a reverse
high voltage will be generated in the coils.
A red LED, and a green LED with a reversed polarity, are connected in parallel
to the terminals of the motor, showing the motor's turning direction. When the
motor turns clockwise, the red LED will be lit; counterclockwise and the green
LED will be on.
SOUNDER
The sounder is controlled by the fourth data line from the Centronic port. This
circuit works in the similar manner as the POWER ON/OFF circuit. The status of
the line controls the On/Off of the second transistor TR2. A voltage oscillation is
therefore produced across resistor R10. The piezo sounder on the robot is
connected in parallel with R10 and produces sound. The data line has to
change its status fast enough to produce a continuous sound.
A Mobile Robot
PARTS LIST
Resistors
R1-4 100ohm 0.25W metal film
R6,7,10,11 1Kohm 0.25W metal film
R5,9 47ohm 0.25W metal film
R8 4.7ohm 0.25W metal film
Capacitors
C1 10uF 16V
Semiconductors
IC1 ILQ1 quad opto isolator
IC2 7805 +5V 1A voltage regulator
TR1,2 C338 NPN transistors
D1,2 1N4148
LED1,2,3 Red 5mm LED
LED4,5 Green 5mm LED
Miscellaneous
RL1,2 12V coil DPDT relays
J1 25pin D type male connector
J2 180 degree DIN socket
SK1 2.5mm power socket
Motor1,2 3.6V DC motors
Sounder Pizero sounder
P1-5 PCB pins
A complete kit for this robot is available from IIE