Logic Tables and Flowcharts
Dr. Jianna J. Zhang
© copyright 2014
Department of Computer Science, Western Washington University
Logic Tables
Logic Tables are graphic representation that
show the relationship between motors, sensors,
and actions.
Action
Motor A
(left wheel)
Motor B
(arms)
Motor C
(right wheel)
Motor A
(left wheel)
Motor B
(right wheel)
Touch Sensor
(objects)
Action
Example 1: Logic Table
1.
2.
The main goal:
1) Make a robot to dance on a
stage
The sub-goals:
1) Walk to the stage
2) Turn towards the audiences
3) Walk left and right
4) Walk back and forth
5) Turn 180 and raise arms up
and down
6) Turn 180 again
7) Repeat step 2) to 6) for 3
times
8) Leave the stage
What do we need?
1. NXT controller
2. Two motors for two wheels
3. One motor for both arms
Action
Motor A
(left wheel)
Motor B
(arms)
Motor C
(right wheel)
Forward
Forward
Off
Forward
Backward
Reverse
Off
Reverse
Left Turn
Off
Off
Forward
Right
Turn
Forward
Off
Off
Raise
Arms
Off
Forward
Off
Lower
Arms
Off
Reverse
Off
Example 2: Logic Table
1.
2.
The main goal:
1) Following a black line on a
flat white surface
The sub-goals:
1) Go forward on the black line
2) Turn left if the robot is on
the right side of the black
line
3) Turn right if the robot is on
the left side of the black line
What do we need?
1. NXT controller
2. Two motors for two wheels
3. A light sensor
The Logic between the light sensor and
motors:
1. (black+white)/2=grey
2. If the light sensor is less than grey, the
robot is close to white surface. It
needs to turn towards black surface.
3. If the light sensor is greater than grey,
the robot is on the black surface. It
needs to turn towards the white
surface.
4. The Logic Table
Action
Motor A
(left wheel)
Motor B
(right wheel)
Light Sensor
(black line)
Forward
Forward
Forward
= grey
Left Turn
Forward
Reverse
> grey
Right Turn
Reverse
Forward
< grey
Basic Types of Flowcharts
Used in this Class
1. Process Flowchart
• show higher level steps with plain English
2. Program Flowchart
• show detailed steps using abstract variables
Elements of Flowcharts
Terminal
On-page
Off-page
Example: start, end, or branch
Conectors
Example: internal/external input or
initializations
Input/output
Process
Action
Pre-defined
Process
Example: “Turn 25” or “go forward”
Example: data file, knowledge base
A File
Files
Decision
Entity
Processing Direction
Example: if touch the wall, go back
else, go forward
Example: sensors, RCX, or motor usually
used in data flowcharts
Example: after turn left, go forward
Why bother?
Start
1. Make plan clear
Walk Forward
• Visual representation
• Good organizing tool
2. Correct logic
Turn 90
• Efficient plan
• Clearly display the logic
B
Walk Right
3. Improve programming
• Quickly pinpoint problems
• Identify bottle necks
Walk Left
4. Example:
make a robot to dance:
Walk Backward
1) Walk to the stage
2) Turn towards the audiences
Walk Forward
3) Walk left and right
4) Walk back and forth
5) Turn 180 and raise arms up and down
A
6) Turn 180 again
7) Repeat step 3) to 6) for 3 times
8) Leave the stage
A
Turn 180
Arms up
Arms down
Turn 180
No
3 times?
Yes
Walk Off
Stage
End
B
Off Page Flowchart
A
Start
Turn 180
B
Come in
from
different
page(s)
Come in
from
different
page(s)
Flowchart for a
Predefined Function
Walk Off Stage
Walk Forward
Arms up
Start
Arms down
Raise Arms Up
Turn 90
Walk Right
Turn 180
Walk Left
Goes to a
different
page.
No
3 times?
B
Lower Arms
Turn right 90
Walk Backward
Walk Forward
Goes to a
different
page.
A
Yes
Walk Off
Stage
Walk Forward
End
End
Page 1
Page 2
Page 3
Examples to Avoid Mistakes
≠
Wrong place to
connect arrows
Arrows must
be connected
with symbols
Loops must go clock
wise direction
Start
Is the touch
sensor
pressed?
Yes
Stop
motors
End
No
Run both
motors forward
Can we do better?
Start
Is the touch
sensor
pressed?
Yes
Stop
motors
End
Start
No
Run both
motors forward
Is the touch
sensor
pressed?
No
Run both
motors forward
Yes
Stop
motors
End
An Example of Process Flowchart
Start
A
Read
Light Sensor
Display
Command
Is
value<40?
Yes
Turn Left
End
Read
Touch Sensor
No
Is
Value=40?
Yes
A
Sing and
Turn 360
No
Turn Right
Yes
Is
value=1?
No
B
B
An Example of Program Flowchart
Variables: L1 = light sensor on port 1
Functions:
1. TurnLeft( ) makes left turns
2. TurnRight( ) makes right turns
3. Display( ) shows message on the LED panel
4. Dance(degree) make several “degree” circles
Start
A
L1=?
Display( )
L1<40
Yes
TurnLeft( )
T1=?
No
L1=40
N
o
TurnRight( )
End
Yes
A
Dance(360)
Yes
T1=1
No
B
B