1. Making of Micromouse www.amitraj.webs.com Amit Raj 2nd Yr ECE
SASTRA University

2. INTRODUCTION
Micromouse is an autonomous robot designed to reach the center of an unknown maze in shortest possible time and distance .

3. www.amitraj.webs.com M I C R O LEFT MOTOR MOTOR N DRIVER T L SESNSORS
SENSOR
ELECTRONICS
SESNSORS
RIGHT
MOTOR

4. Basic components of Micromouse:
Sensors
Motors
Microcontroller
Batteries

5. SENSORS www.amitraj.webs.com
Your mouse is going to need sensors to tell it about itself and its environment.
These are used to detect the presence or absence of walls and to verify your position in the maze.
They will also be important in ensuring that the mouse maintains an appropriate path without hitting any walls

6. Sensors www.amitraj.webs.com
Commonly used sensors in the field of robotics
IR Digital sensors
IR analog sensors

7. IR Digital sensors Transmitter Receiver Advantages
IR led connected to 38KHz oscillator
Receiver
TSOP1738
Advantages
Detects an obstacle at a distance more than 1meter if tuned perfectly.
No ambient light effect.
Easy to use.

8. Designing a transmitter :
Use IC 555 in Astable mode
For approximate 50% duty cycle take Ra = 1 k ohm

9. Receiver :

10. IR Analog sensors Transmitter Receiver www.amitraj.webs.com IR LED
IR Photodiode
Advantages:
Can measure distance up to 15 cm.
Disadvantages:
Responds to IR rays present in ambient light.
Intensity of reflected rays is non-linear with respect to distance of obstacle

11. IR Analog sensor

12. www.amitraj.webs.com Modulate IR rays to avoid Ambient light effect :
Astable oscillator at frequency greater than 1KHz
Transmitter
IR led
ADC
of Micro-controller
High pass filter , Cut-off freq more than 300Hz
Peak Detector
Receiver
IR Photodiode
obstacle

13. High-Pass filter :

14. Peak Detector:

15. Errors involved in mouse movement :
Forward error:
Forward errors begins when a mouse is either too close or too far from the wall ahead

16. Errors involved in mouse movement :
Offset error :
Offset errors, which happens often, is caused by being too far to the left or to the right as you pass through a cell

17. Errors involved in mouse movement :
Heading error:
Heading error is known as pointing at walls rather than down the middle of the cell

18. SENSORS Commonly used Sensor arrangement : www.amitraj.webs.com
Top Down
Side Looking
SENSORS

19. Top Down

21. Side looking sensors :

22. ADC conversion complete
Initialize ADC
Select ADC channel
Start ADC
ADC conversion complete N0
Yes
Read ADC value
Stop

23. www.amitraj.webs.com Side looking
Sample code for ADC conversion in AVR controllers :
Unsigned int left_adc;
left_adc = adc(0xE0);
unsigned int adc(unsigned int temp) {
ADMUX = temp; //selects ADC channel
ADCSRA |= 0x40; //starts ADC
while(conversion_not_over()); //waits till ADC conversion completes
ADCSRA |= 0x10; // clears ADIF flag
return(ADCH); // returns ADC result }
int conversion_not_over(void) {
unsigned int temp;
temp = ADCSRA;
temp = temp & 0x10; // checks for ADIF flag
return(!temp); }

24. Reducing error using PD controller :
Motors

25. Error calculating: www.amitraj.webs.com If wall is on both sides
err = left_adc – right_adc;
If err is +ve
Mouse is near to left wall and as a correction it has to move towards right wall
If wall is only on leftside
err = left_adc – reff_value;
If wall is only on rightside
err = right_adc – reff_value;
Mouse is near to right wall and as a correction it has to move towards left wall

26. Implementing PD controller:
err_d = err – err_past;
adj = err * kp + err_d * kd ;
kp is proportional controller constant
kd is derivative controller constant
The value of adj is used to either speed up or speed down one of the wheel .

27. DC Motor www.amitraj.webs.com
DC Motors are small, inexpensive and powerful motors used widely.
These are widely used in robotics for their small size and high energy out.
A typical DC motor operates at speeds that are far too high speed to be useful, and torque that are far too low.
Gear reduction is the standard method by which a motor is made useful .
Gear’s reduce the speed of motor and increases the torque

28. Choosing a DC Motor www.amitraj.webs.com DC Motor with Gear head
Operating voltage 12V
Speed
Depends on our application
Some available speeds in market
30 RPM
60 RPM
100 RPM
150 RPM
350 RPM
1000 RPM

29. Drive basics of DC Motor
Red wire
Black wire
Direction of rotation
Positive
Negative
Clock wise
Anti clock wise
Logic
Direction 1
Clock
Anti clock

30. Bi-Direction control of DC Motor
H-Bridge Ckt using transistors for bidirectional driving of DC motor
Direction
Pulse to
Clock wise
A and C
Anti Clock wise
B and D

31. H-Bridges in IC’s to reduce the drive circuit complexity
The most commonly used H-Bridges are L293D and
L298
L293D has maximum current rating of 600ma
L298 has maximum current rating of 2A
Both has 2 H-Bridges in them
These are designed to drive inductive loads such as
relays, solenoids
Can be used to drive 2 DC motors or 1 stepper motor

32. PWM

34. STEPPER MOTOR www.amitraj.webs.com
STEPPER MOTOR is a brushless DC motor whose rotor rotates in discrete angular increments when its stator windings are energized in a programmed manner.
Rotation occurs because of magnetic interaction between rotor poles and poles of sequentially energized stator windings.
The rotor has no electrical windings, but has salient and/or magnetized poles.

35. www.amitraj.webs.com 5 – Lead stepper 4 – Lead stepper

36. Full Step driving of Stepper Motor
Full step wave drive 4 3 2 1

37. Full Step driving of Stepper Motor
Full step 2 phases active 4 3 2 1

38. Half Step driving of stepper motor4 3 2 1

40. Choosing a Stepper motor
12 V or 5 V operating voltage
1.8 degree step
6 Lead
250 to 500 ma of current or
Coil resistance of 20 ohms to 40 ohms
Size and shape depends on application
In most of the robotics cube shaped motors are preferred with frame size of 3.9 to 4 cm

41. www.amitraj.webs.com Commonly used IC’s for driving Stepper motor
ULN2803
It has 8 channels
It channel has maximum current rating of 500ma
can be used to drive 2 unipolar stepper motors
L293d
L297 & L298
UDN2916

42. ULN2803

44. Bi – Polar driving of Stepper MotorC D 1

45. www.amitraj.webs.com 5 – Lead stepper 4 – Lead stepper

46. Sample program www.amitraj.webs.com for(p=0;p<=20;p++) {
PORTD=0xA9;
delay(65);
PORTD=0x65;
PORTD=0x56;
PORTD=0x9A; }
void delay(unsigned int m) {
unsigned int n;
while(m--)
for(n=0;n<=100;n++); }
With this SW Steppers can’t be controlled individually

47. www.amitraj.webs.com SW for steppers : Use timers to create delay.
Use Clear Timer on Compare match or
Normal Mode

48. www.amitraj.webs.com Initialize timer Interrupt routine
Give Pulse to stepper
Start Timer
Is Stepper target reached
Update Output compare register No
Wait
Reti
Yes
Stop timer

49. Chopper Driving: www.amitraj.webs.com
For better performance of Steppers they should be over driven and current should be limited .
For example a 5 V 500ma motor can be driven at more than 15V but current in the coil should be limited to approximately 500ma .

50. www.amitraj.webs.com Methods of current limiting :
Traditional method of using a resistor of appropriate power in series with common terminal.
This method is not recommended as there will be huge power wasted in the series resistor.

51. Best method of current limiting :
Pulse Width Modulation
Motors should be driven at 3 to 4 times the rated voltage.
Measure the current in the coil if it raises to 10% more than the limit switch off the supply to motors .
If it falls to 10% below the limit switch on the supply to motors .
Few IC’s that can do the current chopping
1. L297 & L298
2. UDN 2916
3. UCN 5804

52. www.amitraj.webs.com Microcontroller:
Choose the controller that has sufficient
Amount of FLASH memory to store your program
Amount of RAM memory for variables
Number of Timers
Min of TWO 16 bit timers or ONE 16 bit timer with TWO output compare channels and ONE 8 bit timer
Number of ADC channels
Good operating speed
ATMEGA32 of Amtel made is one that is suitable

53. www.amitraj.webs.com Batteries:
Choose batteries that can provide high voltage and high power with low weight
Should have current capacity more than 700 mah
Ni-MH & Ni-Cds
Can provides high current at 1.2 V
Can be charged by Constant Current or Constant Voltage chargers
Li – Ion
Can provide high current at 3.6v
Should be charged using CCCV charger .

54. You can download this presentation at www.amitraj.webs.com