1. Building Automated
Robots
Sagar N
&
Sanjay R
III year ECE

2. What is an automated robot?
A machine which can
accomplish a predefined task
without external control.
It must possess sufficient
intelligence to take decisions.
It must not receive any kind
of aid from an external agent.
It should have an on-board
power source.
Micromouse video.

3. Structure Of a Simple Robot
A robot designed to accomplish a fairly difficult task must necessarily
have a microcontroller.
Input devices are interfaced to microcontroller through circuit elements
which convert analog signals to digital signals.
Output of the microcontroller is interfaced to actuators through buffers
and drivers.
Feedback can be used for efficient control.
Power unit is essential to supply power to the various blocks.

4. A line follower…
Sensors act as inputs to the microcontroller.
Sensor outputs are given to the microcontroller after analog
to digital conversion.
Microcontroller is the basic intelligence unit which
processes the input and controls the actuators – motors in
this case.
Motor drivers are either current amplifiers or pulse
sequencers or both. They are used to drive the motors and
prevent the microcontroller from getting burnt.
A power supply unit is designed so as to provide proper
voltage levels to microcontrollers, drivers and motors.
Stabilized power to the microcontroller is an absolute
necessity.

5. Sensors
A LED is diode which emits light when forward
biased by sufficient voltage.
LDR: Its resistance varies with incident light intensity.
Phototransistor is a transistor in which, the base
current is proportional to IR Rays and, to a certain extent, visible
light incident on it.
IR LED: This emits infrared rays when forward biased.
Commonly used reflective sensors:
-LDR and LED pair
-Phototransistor and IR LED pair

6. LDR and LED pair
LDR has two terminals similar to a normal resistor but the
resistance varies inversely with the light intensity.
Its response is most significant in the visible region of
spectrum.
White LEDs give better performance as compared to other
types.
A small bulb can be used instead of LED but it consumes
more power and dissipates a lot of heat.
This sensor pair is better suited for light sensing bots and
not for reflective sensing.

7. Phototransistor and IR LED Pair
IR LED is similar to normal LED except that it
emits IR Rays.
Phototransistor generally has two terminals-
collector and emitter –base drive is proportional
to light intensity.
IR LED emission strength increases by decreasing
the series resistance and phototransistor
sensitivity increases by increasing the collector
resistance.
Phototransistor response is best for IR radiation.

8. Spectral distribution of IR LED and
phototransistor sensitivities

9. Circuit Connections

10. Interface to microcontroller
Microcontrollers do not recognize voltages
other than standard TTL levels.
Comparators are used to convert the input
analog signals to digital.
Op amps LM324 can be used as
comparators; LM339 is an IC designed as
a comparator-they can be used for higher
frequency operations.

11. Complete circuit diagram for IR LED -
phototransistor sensor

12. Power Supply to Microcontrollers (µC)
For proper functioning of µC a constant
power supply is necessary.
A Voltage regulator is used to give a
constant 5V to the microcontroller.
IC 7805 is generally used as a voltage
regulator.

13. Circuit Connections

14. Motors
Two types of motors are generally used :
-DC Motors
-Stepper Motors
DC Motors:-Advantages: Small and light, cheap, consumes
less power.
Disadvantages: Inaccurate, Complicated closed loop
control, needs gear boxes.
Stepper Motors:- Advantages: Very easy to control (Open
loop), very accurate.
Disadvantages: Heavy, costly setup, consumes more power.

15. DC Motors-General
It has two terminals. Voltage is applied to
the terminals and the motor begins to
rotate.
Induced voltage opposes the current.
Applying more load to the dc motors drops
the speed & increases current, thus
increasing the power consumption.
Stall torque- A load just sufficient to stop
the dc motor from turning.

16. DC Motors-Working
Structure:
Rotating armature-electromagnet.
Armature enclosed between a set of permanent
magnets.
Commuter – Rotary switch
which reverses the direction
of electric current twice
every cycle.

17. DC Motors-Torque and R.P.M
Two important parameters-Torque, R.P.M.
Torque is the amount of turning force.
T=Kt*I I: Current through armature.
R.P.M is rotations per minute and is proportional
to the voltage applied.
E=Ke*w w: Angular velocity
• V=Rin*I + Ke*w

18. DC Motors-Gear Box
DC Motors generally have thousands of R.P.M.
Torque is very less without gears.
Gears are used to decrease the R.P.M and in
effect increase the torque.
No gears and don’t expect your robot to move.
Choose gears appropriately.

19. DC Motors– Speed Control
Speed is proportional to the voltage applied
across the motor terminals.
Pulse Width Modulation is used.
Pulses of definite frequency is applied whose ‘ON’
Time and ‘OFF’ Time decide the average voltage
applied.
PWM is easy to achieve using a micro-controller.

20. DC Motors-Speed Measurement
PWM varies the speed but exact speed control
requires speed measurement.
Some DC Motors come with built in encoders.
For DC Motors without such a setup, sensors
must be used to measure the R.P.M and thus the
speed.
!idea! –Make some notches on the wheel and
keep track of number of notches per second.

21. DC Motors- Motor Drivers
Microcontrollers can supply 5V but not the
enormous current required by motors.
DC Motor Drivers act as buffer and in this case –
current amplifiers.
H –Bridge.
Motor Driver IC-L293D.
Different voltage can be given to motors.

22. L293D Circuit Connections

23. Stepper Motors-General
Stepper is used for its accurate and easy control.
Stepper motor has 4 control wires.
4 independent pulse trains to each of the 4
control wires.
Two types of stepper motors:
- Unipolar, Bipolar.

24. Stepper Motors-Working
Shaft is a permanent magnet.
Imagine a compass needle
surrounded by four electro-
magnets.
Magnetising the coils one after
the other makes the shaft
to rotate.
Here the step angle is 90 deg.

25. Stepper Motors-Working
If the number of electro-
magnets are more, then step
angle reduces.
In commercial stepper motors
step angle will be approx 1.8
to 7.2 deg.
Computers are great at
switching things on and off.
Thus with 4 pins dedicated to a
stepper, speed can be easily
controlled without feedback.

26. Stepper Motors-Control Sequences
Full Step Sequence –Type 1
A B C D comment
1 0 0 0 take a step clockwise
0 1 0 0 another step clockwise
0 0 1 0 another step clockwise
0 0 0 1 another step clockwise
0 0 0 1 Wait right here!
0 0 1 0 Take a step back.
Winding A 1000100010001000100010001
Winding B 0100010001000100010001000
Winding C 0010001000100010001000100
Winding D 0001000100010001000100010

27. Stepper Motors-Control Sequences
Full Step Sequence-Type 2:More torque
A B C D comment
1 1 0 0 take a step clockwise
0 1 1 0 another step clockwise
0 0 1 1 another step clockwise
1 0 0 1 another step clockwise
1 0 0 1 Wait right here!
0 0 1 1 Take a step back.
Winding A 1100110011001100110011001
Winding B 0110011001100110011001100
Winding C 0011001100110011001100110
Winding D 1001100110011001100110011
time --->

28. Stepper Motors-Control Sequences
Half Step Sequence: More accuracy
A B C D comment
1 0 0 0 start here
1 1 0 0 half a step clockwise
0 1 0 0 complete the first full step
clockwise
0 1 1 0 another half step
0 0 1 0 complete that step
0 0 1 1 another half step
0 0 0 1 complete that step
1 0 0 1 final half step
1 0 0 0 back to the starting
position

29. Stepper Motors-Types
Two types: Unipolar and Bipolar.
Unipolar was discussed till now.
Bipolar gives more torque and size is less.
Drivers are expensive.

30. Interface to Microcontrollers
(Uni-Polar)
Unipolar stepper has 5 or 6 terminals.
4 control terminals and two power terminals.
To drive Unipolar steppers, current amplifiers
which amplify current in only one direction will
suffice.
ULN2803 is an IC designed as a current
amplifier.L293D can also be used.

31. ULN 2803

32. Interface to Microcontrollers
(Bi-Polar)
Current flows from one terminal to other.
H-bridge must be used.
Driver ICs:L293D,UCN5804B,SLA7024.
Sequencing ICs which generate pulses are
available(e.g.L297) but are costly.
Sequencing can be done by microcontrollers.

33. Block Diagram Of L293D

34. Inside a microcontroller