RobotC

1
RobotC A Tutorial II
2
Learning from yesterday

• The IDE
• Functions and usage of various panels
• Top Menubar
• Side Functions panel
• Code Window
• Error Window
• Compiling/Downloading the code
• Running the program
• C Programming Syntax
• Capitalization
• Whitespaces
• Comments
• Variables
• Boolean Algebra

REVISION
3
Learning from yesterday

• Control Structures
• Tasks
• Functions
• If-Else/Switch
• While/For
• Today we are going to look at specific commands
  and
• options available in RobotC for controlling the
  NXT

REVISION
4
Section Overview

• Reserved Words
• Motors
• Timers
• LCD Display
• Sensor Configuration
• Debugger Usage
• Tasks
• Functions
• If-Else/Switch
• While/For

SECTION 3
5
Overview

• RobotC has a variety of commands, interfaces and
  options which deal specifically with robots. Some
  of these are
• Reserved words like motor, timers (keywords)
• Sensor interfaces
• Live debugger

ROBOTC FEATURES
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Keywords

• RobotC has a variety of keywords which are used
  for issuing specific commands to the NXT
  controller
• As it is not possible to cover all the commands
  in detail here, only the main ones will be
  discussed.
• Explore the rest of the options by using the
  help available within the programming environment
  or online version (as explained earlier)

ROBOTC FEATURES
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Motors
Motor control Turn on/off at a certain power
level General Syntax motoroutput
power Parameters Output Determine the motor
to affect. This can be motorA, motorB,
motorC This command just gives power to the 3
output ports A, B, C in a certain fashion. This
can also be fed to a circuit to control other
devices Power Determines the power at which
the motor is to be run. This can take any integer
value from -100 (full reverse) to 100 (full
forward) Examples motormotorA 60 //Run
motor A at 60 power motormotorB -50 //Run
motor B in reverse at 50 motormotorC 100
//Run motor C at full power forward
ROBOTC FEATURES
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Motors 5 minute activity
Using the simple motor command, try to write a
program that spins the RoboCar as fast as
possible How fast does it rotate? (RPM)
ROBOTC FEATURES
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Motors 5 minute activity
How did you do? Here is one solution task
main() motormotorA 100
motormotorB -100 while(true) where
you turn both motors at full power, opposite
direction. At this point, just take a moment to
think of all the other factors which may have
affected your spin rate (battery power, weight
imbalance, friction, etc) Robust code accounts
for as many uncertainties as possible
ROBOTC FEATURES
10
Timers Wait Timers

• The wait commands allow you to insert delays into
  your program. Its like starting a stop watch and
  pause the execution of your program.
• The pause in execution means that the next
  command will not be executed till after the timer
  expires. However, the actions due to the commands
  already issued will continue.
• There are two commands related to this
• wait1Msec(wait_time)
• wait10Msec(wait_time)
• Parameters
• wait_time Refers to the time for which the
  program pauses before proceeding to the next
  step. The units are either milliseconds (1/1000
  of sec) or 10s of milliseconds (1/100 of sec)

ROBOTC FEATURES
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Timers Examples
The following examples uses the wait function to
allow the motors to operate for 1 second at a
time.
ROBOTC FEATURES
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Motors 5 minute activity
Using the encoder command, try to write a program
that rolls the car forward a distance of
approximately 2 feet
ROBOTC FEATURES
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Motors 5 minute activity
How did you do? Does your code look something
like this? task main() motormotorA
100 motormotorB -100
wait1Msec(2000) // however long it takes to go
2ft
ROBOTC FEATURES
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LCD Display

• The LCD display on the NXT is a 6 line display
  that can be controlled via functions in RobotC.
• It can support a display of 16 characters per
  line
• The display is an extremely useful resource
  during the debugging phase, for observing the
  values of various inputs and outputs.
• If left unmodified, the LCD will display the
  readings of the input sensors and the output
  power level of the motors.

ROBOTC FEATURES
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LCD Display - Functions
Two functions that may be useful to access the
LCD are nxtDisplayStringAt(xPos,yPos,text,var1,va
r2,var3) print text eraseDisplay() clear the
NXT display Parameters xPos - Number of pixels
away from the left of the display that you want
your string to be printed at. yPos - This
integer value is the number of pixels away from
the bottom of the display that you want your
string to be printed at. text - The text
parameter is what shows up on the screen. This
will be a string enclosed in quotes up to 16
characters. You may also display up to 3
variables in this string by adding d, f
(conversion specifications) up to three times.
var1, var2, var3 - These (optional) parameters
define which variables will be displayed to the
screen and each must correspond to a separate d,
f within the text parameter.
ROBOTC FEATURES
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Motors - Encoder
Each standard Lego motor has an inbuilt encoder
that can be used to measure the amount the motor
has turned by, or turn the motor by a specific
number of degrees General Syntax (to obtain the
reading) myVar nMotorEncoderoutput General
Syntax (set the turning amount) nMotorEncoderTarge
toutput numCounts Parameters output
Determine the motor to affect. numCounts The
number of encoder counts that the motor must turn
before stopping myVar a variable that gets
assigned the current value of the encoder
ROBOTC FEATURES
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Motors - Encoder
Encoder Example (To turn to desired value by
setting) // Set degrees that motor A must turn to
1000 nMotorEncoderTargetmotorA 1000 // Turn
on Motor A. It will automatically stop // after
turning for the desired amount motormotorA 75
ROBOTC FEATURES
Encoder Example (To turn to desired value by
observation) // Turn on motorA until it has
turned 1000 degrees motormotorA
75 while(nMotorEncodermotorA lt 1000)
motormotorA 0 // requires explicit stop
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Motors 10 minute activity
Write a creative programming solution to navigate
the following course without using any
sensors. Based on what you have already learned
ROBOTC FEATURES
2 ft
1 ft
2 ft
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Motors 10 minute activity
Here are a couple of suggestions Go straight for
a fixed time (calculated by trial and error) Then
turn right and go further straight for some more
time (again calculated by trial and error) Then
turn left and go straight OR Measure the
circumference of the wheel to get how much the
car will travel in one revolution. Use this
number and the distances mentioned on the track
to get the desired number of revolutions before
turning Set the encoder accordingly and
GO! OR Mix the above 2 methods
ROBOTC FEATURES
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Sensor Interface

• RobotC has an extremely powerful sensor interface
  which may be used to communicate with Lego and
  other third party sensors.
• Ideally, RobotC sensor interface provides an
  enormous degree of freedom to the programmer.
• It provides several options for configuring the
  sensor ports to
• Read the raw value Mainly used for self
  designed sensors
• Communicate via the I2C interface Mainly used
  by third party providers
• Work using standard protocols and thresholds with
  the standard Lego sensors

ROBOTC FEATURES
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Sensor Interface - Accessing
The sensor interface in RobotC may be accessed
through the Robot Menu on top of the IDE. The
steps for accessing the sensor menu are as follows
ROBOTC FEATURES
Click on the Robot Button on the top menubar and
select the Motors and Sensors Setup box
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Sensor Interface - Accessing
Click on the management tab. This brings up the
options to select the kind of sensors that are
displayed
ROBOTC FEATURES
Tick the bottom 3 boxes. Unless you want to use
old RCX Sensors
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Sensor Interface - Accessing
A popup will occur as depicted. Choose the A/D
sensor tab. A/D stands for Analog to Digital
ROBOTC FEATURES
Type of sensors
You can configure up to 4 sensors
Fields for specifying the names of the sensors
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Sensor Interface - Accessing
Give a name to the sensors you intend to use and
configure it to a certain type from the drop box
ROBOTC FEATURES
Type of sensors This one is being configured as
SONAR
names given to the three sensors
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Sensor Interface - Accessing
Click on OK. This will create some auto-generated
lines of code at the top of the program. This
means that the sensors have been configured for
use in the program.
ROBOTC FEATURES
Observe, No line numbers
Auto-generated code. DO NOT EDIT THIS
Given sensor names
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Sensor Interface - Accessing
After configuration, using the sensor values in
the program is a trivial task two methods of
obtaining the sensor values myVar
SensorValue(sensor_name) myVar
SensorRaw(sensor_name) The first method returns
the configured sensor value. Second one returns
the raw value. Parameters sensor_name This
denotes the name assigned to the sensor in the
configuration step Both may be used to obtain
sensor readings (either raw or calibrated) The
choice of method depends upon intended use
ROBOTC FEATURES
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Sensor Interface
Each sensor after configuration has two types of
values Raw value This is the raw value that
the NXT observes based on the voltage across the
input port. Every sensor has a raw value reading.
Varies between 0-1023 (10 bits) Sensor Value
Obtained after application of thresholds to the
raw value based on the configuration. Range
depends on the configuration. More apt as per
application Example For a sensor configured as
a touch sensor
ROBOTC FEATURES
Raw Value 0-512 512-1023
Sensor Value 0 1
State Released Pressed
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Sensors 10 min activity
Configure the sensor on port 1 to be a light
sensor. Write a snippet of code that looks at
the sensor reading and displays a Light! or
Dark! message on the NXT screen when the light
sensor is over a light or dark surface.
ROBOTC FEATURES
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Sensors 10 min activity
Did your program look like this??
ROBOTC FEATURES
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Debugging
Debugging is one of the most difficult parts of
writing code Fortunately, RobotC has an
extremely powerful debugger, much better than
other languages for similar functions
ROBOTC FEATURES
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Debugger Not Compiler
Debugging generally refers to solving logical
fallacies in the code. The compiler will give
ERROR messages ONLY for syntax errors. You cannot
run a code with syntax errors The compiler does
highlight potential logical flaws in the form of
WARNINGS and INFO messages. But these MAY or MAY
NOT be the source of the logical problems. It
is a good practice to make sure you have fixed
all warning and info messages as well.
ROBOTC FEATURES
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Debugging - Options
Compiling and loading the program on the brick
will enable several new debug options which were
previously disabled or inactive
Each of these windows is significant for a
particular kind of error tracking The most
important ones are 1. Global Variables 2. NXT
Devices 3. Task Status
ROBOTC FEATURES
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Debugging - Example
Consider the example on the next slide for the
purpose of debugging There are intentionally
created errors in that program Lets see if they
can be identified using the debugger
ROBOTC FEATURES
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ROBOTC FEATURES
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Debugging
What errors can be identified from here??
This variable is not being updated, so mustnt be
assigned
ROBOTC FEATURES
These variables have identical values assigned,
but according to sensors they should be different
More clues
36
Lets see how accurate we were
variable light_sensor is not assigned
ROBOTC FEATURES
variable dist_sensor is getting light_sensor
reading
Thus we were correctly able to identify all errors
37
Debugging
Lets see how the debugger looks with the
corrected programs
ROBOTC FEATURES
All seem good and in correspondence
PERFECT!!!
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Lets correct the program
Observe the color of these Xs. Recall from
yesterday. These are simple information
messages. Why do you think they are reported?
The compiler is trying to tell you that though
you have declared and assigned these variables,
you have not used them anywhere in the program.
So it is trying to save your memory and flag
potential errors. Sometimes, you tend to declare
a variable with the intention of using it but end
up using the wrong variable with a similar name.
This can lead to really unpredictable
results. One of the most difficult logical errors
to catch
ROBOTC FEATURES
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Debugging
One of the major sources of problems is
disconnection of an input sensor from the port,
either due to a loose connection, or inadvertent
connection to the wrong port In this example, the
light sensor from port A is connected mistakenly
to port C Observe how the raw value of port A is
saturated at 1023 while there is an undesired
value on port C
ROBOTC FEATURES
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Debugging
One common problem with many codes is missing
timing delays. Such mistakes cause a lot of
confusion and undesirable results These are
difficult to catch by using the debugging
techniques discussed They can be better examined
by using the step by step debugger of RobotC
ROBOTC FEATURES
These commands allow step by step execution,
hence giving more control for analysis
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Debugging - Example
Consider a program that moves the car forward
till the light sensor reading is above a
threshold (i.e. it is bright). If it sees a
shadow, or darkness, i.e. the value of the light
sensor drops, it backs up for some distance and
then tries again
ROBOTC FEATURES
This program has the error that as soon as the
car sees the black line or black shadow, it stops
rather than going back.
42
Debugging - Example
Lets try to use the debugger stepping to solve
the problem. We can see that if we select
continuous update of the values, then the green
line moves extremely fast and we are unable to
understand anything.
ROBOTC FEATURES
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Debugging - Example
The way around this is to suspend the program by
clicking the suspend button. This pauses the
execution of the program leaving all the
variables and sensors intact The sensor readings
and motor tachometer readings keep getting
updated even in the suspend mode
ROBOTC FEATURES
Then click the step into button. This will cause
the green line to be replaced by a yellow one
which will stay on a specific statement You are
now using the stepping mode of the debugger
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Debugging - Example
Each successive pressing of the Step Into button
will advance the program step by step
ROBOTC FEATURES
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Debugging - Example
Going through a few iterations in a stepwise
manner, we can see that reason for the car to not
back up is the lack of delay while running in the
reverse direction This can be rectified by
adding a simple delay command after issuing the
commands for the car to go backward
ROBOTC FEATURES
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Common Errors
What is the error in the code below?
There is no break statement. So all statements
after case 2 will execute! So even though the
motors are supposed to run at 20 power only,
they will instantly cycle through 20, 30 and
finally 100. So you will always see motors
turned on at full power
ROBOTC FEATURES
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Common Errors
What is the error in the code below?
In the if condition, the variable has to be
checked to be equal to 30. So should be used
(binary operator) In the current form, the
variable will be assigned the value 30 inside the
if. This overall operation returns 30, which in
Boolean terms is true. So motors will always run
at 20 power
ROBOTC FEATURES
48
Summary

• In the final section, you learned
• RobotC specific keywords and usage
• Sensor configuration and usage
• Use of the debugger and various methods of
  debugging
• This completes the basic tutorial on RobotC.
• You should now be familiar enough with the basic
  concepts to build sufficiently complex systems

SECTION SUMMARY
49
Help

• In case you need help
• Have a look at http//www.robotc.net/teachingminds
  torms/
• Use the in-built help in the IDE
• Ask Google
• If you are still stuck, ask your TF/TA!!!
• and like mentioned initially, always remember -
  your design and needs should guide the language
  and not the other way around!!

SECTION SUMMARY
50
Questions???
QUESTIONS
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Exercise
Write a program make the RoboCar go around in
circles of a certain fixed radius (say 1 ft)
EXERCISE
52
Exercise
Write a program make the RoboCar go straight for
2 feet, turn around, return to the start
position, and repeat once more.
EXERCISE
53
Exercise
Write a program that will move the RoboCar
forward until it sees a second black line, then
turn around three times and stop.
SECTION SUMMARY
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Backup Slides
BACKUP SLIDES
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Motors - Synchronization
Synchronization Used to ensure movement of both
motors in synchronization (either same speed or
different) When the motors are not perfectly
aligned, the program makes adjustments to their
power to bring them together again. General
Syntax (3 steps) nSyncedMotors
syncPair nSyncedTurnRatio ratio motoroutput
power Parameters syncPair Denotes the pair
of motors to synchronize. This can take values
synchAB, synchAC, synchCB, synchCA and synchBA,
synchNone. The first of these denotes the master
and the second one the slave ratio A value
between 100 to -100 denotes the ratio of the
speeds between the master and the slave. Negative
denotes the opposite direction
ROBOTC FEATURES
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Motors - Synchronization
Synchronization Example // Synchronize motor A
and B with A being the master and B being the
slave nSyncedMotors synchAB // Specify the
turn ratio. nSyncedTurnRatio 50 // This means
that the power of the slave motor (B here) must
be 50 of the power to A // Specify the power of
the master motor (motor A) motormotorA 75
ROBOTC FEATURES
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Motors - Other

• There are a variety of other degrees of control
  which can be implemented in motors.
• May not be useful in the immediate context but
  good to know.
• Use the help menu to get elaborated details
• bFloatDuringInactiveMotorPWM - Indicates whether
  to float the motor inputs or apply immediate
  brakes when attempting to stop
• nMotorRunState - Contains the state (idle,
  ramping up or down, steady state, holding encoder
  position while stopped) of a motor.
• bMotorReflected - Boolean flag to indicate
  whether motor direction should be flipped or
  reflected from the normal.
• nMotorPIDSpeedCtrl - Turn on the PID controller
  for that motor.

ROBOTC FEATURES
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Motors PID Controller
Turn on the PID controller for that motor. The
PID control adjusts the actual amount of power
sent to a motor to match the desired value,
specified in the program. General
Syntax nMotorPIDSpeedCtrloutput
optionValue Parameters Output Determine the
motor to affect. optionValue Enable or
disable PID control for the given motor. This can
take the value mtrNoReg to disable the PID or
mtrSpeedReg to enable to PID Examples nMotorPIDSp
eedCtrlmotorA mtrSpeedReg motormotorA
60 //Run motor A at 60 power level,
regardless of the conditions
ROBOTC FEATURES
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Motors 10 minute activity

• Try the following activities
• Turn on the PID controller for the motors. Run
  the motors at speeds less than 100 (say 50). Try
  varying the weight on the car by adding or
  removing something. Does it still run at the same
  speed? Do you see the PID controller working?
• Repeat the activity done before (of spinning the
  car) by synchronizing the two motors in opposite
  direction

ROBOTC FEATURES
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Sensor Interface - Advanced
In case the type of sensor need to be changed
dynamically, based on some other input
parameters, there are several other methods to
configure sensors, const tSensors sensor_name
sensor_port SensorTypesensor_name
sensor_type Parameters Sensor_port The input
port to which the sensor is connected (S1, S2, S3
or S4) Sensor_type The type of configuration
for the sensor (similar to dropdown menu on the
previous slides) Example const tSensors
myOtherTouchSensor S3 SensorTypemyOtherTouchSe
nsor sensorTouch This command configures
the input from port 3 to behave as a touch sensor
input
ROBOTC FEATURES
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Debugging Sensor values revisited
Recall the previous discussion about the
difference between the raw value and the sensor
value.
In the following example, the same light sensor
was connected to port 1 and under identical
circumstances configured as an active light
sensor and a Sound sensor. It can be clearly
seen that despite the raw value being the same
(as expected, due to the same circumstances), the
sensor value is different, because it is
configured differently
ROBOTC FEATURES
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Exercise
Write a program that has the capability of
navigating the given maze using just a touch
sensor and the internal capability of the Lego
motor to measure the angle. (Hint its not as
complex as it looks)
start
EXERCISE
finish
63
Exercise
Can this navigation be done using just a single
light sensor (no line to follow here)? If yes,
how? If not, then under what conditions or with
what modifications to the maze would it be
possible?
start
EXERCISE
finish
64
Exercise
Write a program that is capable of following a
thin black line (around 1) on a black
background. Your program should be robust enough
to do this task regardless of the shape that the
line makes. The fastest team wins!
SECTION SUMMARY
65
Exercise
If the line was 4 thick instead of 1. How can
you improve your program? Can it go faster now?
Does your logic change?
SECTION SUMMARY