Mentor Sheet
2nd meeting
Agenda for October11, 2007
1. Why sensors?
2. Touch and light sensors
3. Forks and loops
4. Touch sensor bumper car
5. Introduce Sumo Challenge
Equipment required:
 Completed taskbot
 Computer with ROBOLAB 2.9
 Touch, light, distance, and sound sensors
 Worksheets for your student
Concepts introduced:
 Importance of sensors
 Forks and loops
 Design planning
New icons:
NXT Wait
for Push
NXT Wait for
LetGo
NXT Wait for
Light
NXT Wait
for Dark
NXT Wait for
Brighter
NXT Wait
for Darker
NXT Touch
Sensor Fork
NXT Light
Sensor Fork
Fork Merge
Start of Loop
End of Loop
Input 1
“Structures”
menu
“Forks”
Submenu
“Loops”
Submenu
All of the “Wait for” icons are found in the “Wait for” menu. The forks are found in the
Forks submenu of the Structures menu. The loops icons are found in the loops submenu
of the structures menu.
Please remember to have your robot charged!
1. Why use sensors? (5 minutes)
a. Ask your group what a sensor is. Ans: Allows you to take in some sort of
data from the environment. An easy way to think about it is that sensors
are similar to the way humans have 5 senses that they can use.
b. Why use sensors? Activity
i. Select two students and ask them to stand up facing the same
direction and walk to some landmark (i.e., wall, desk, trash can,
etc.). They should do it without any difficulty.
ii. Now have the same two students repeat the activity with their eyes
closed and change the directions from walk to a certain landmark
to walk a certain number of steps or for a certain length of time.
They should end up in different places and not at the landmark.
iii. Part ii highlights 2 problems involved with hard coding values
instead of using sensors. First, the same commands can produce
different results for relatively similar robots. Second, in order to
ensure perfect performance, the command must be continually
fine-tuned. Using sensors (part i), allows for a robot to operate in a
dynamic, changing environment.
2. Introduction to the NXT sensors
a. Each NXT kit comes with 2 touch sensors, a light sensor, an ultrasonic
distance sensor, and a sound level (dB) sensor.
b. These sensors work by taking information from the environment, turning
that information into an electric signal, and turning that signal into a set of
numbers that the computer can understand and a set of numbers that make
sense to humans.
c. The NXT’s view menu provides a good general introduction to the
sensors.
i. Hook up the Distance sensor (must be in Port 4) and use the view
menu to get an idea of the readings you get.
ii. Repeat with the sound level and light sensors (Can be in ports 1-4)
1. Take note of how light values change on different colors, in
different environments (i.e. shade), and at different heights.
Explain that the sensor reads from 0-100, where 0 is the
darkest reading possible and 100 is the brightest reading
possible.
2. BE SURE TO USE REFLECTED LIGHT WHEN
TAKING READINGS FROM THE LIGHT SENSOR
iii. Because the touch sensor can only be pressed or not pressed, we’ll
introduce it in our first programming example of the day.
3. Introducing loops and forks
a. You want your robot to go forward until the touch sensor is pressed, stop
for 2 seconds, and back up for two seconds. What do you do? The
following code assumes that the touch sensor is in port 3.
b. What if you want the program to repeat 2 (or any number) of times?
i. You could continue to repeat the same code, but after a few times
that gets messy and confusing.
ii. This is where loops come in handy. They repeat the code
contained inside of the loop for the number of times specified. The
following code will cause the same program above to run 4 times.
The numerical constant is located in the Modifiers menu.
iii. There are many different types of loops, several of which may be
helpful including the continual loop (the purple one). Use this as
an opportunity to show context help (Apple + H or select Help,
Show Context Help from the menu). Mouse over a few
conditional loops using sensors to show how they work.
c. Forks
i. Use the context help function to let students figure out how the
touch sensor fork functions. Then ask them to complete the
following problem.
ii. Suppose you want to make some sort of controller that will allow
the robot to travel forward for 2 seconds and then turn left or right
depending on your desire at that point in time. Develop a code
using a fork sensor and continual loop. Note: There are several
ways to turn, and the wait fors could be changed to a time or
something else. This setup allows for complete control of the
length of the turn.
4. Touch sensor bumper cars – similar to avoider, but much simpler…
a. Car should explore an enclosed area
b. Upon hitting an object it should back up and turn
5. Sumo Challenge – End of year contest, more details to follow