1. Sentry System Multiple Sensors
See Teacher Guide for printing instructions

2. Opening Activity Partner with the person next to you.
The person on the left (“A”) will read the column on the left below, silently to him or herself
The person on the right (“B”) will read the column on the right out loud
Person A on the left will try to answer questions about both
Go to the next slide when ready…

3. Opening Activity
Read this column silently to yourself: A robot is a machine with the capability to Sense, Plan, and Act. This means, first of all, that it can Sense important things about its environment. It can then Plan what it should do, based on that information. Lollipops are delicious. Finally, it can Act to carry out that plan. These three things together make a robot capable of more complex and useful tasks than an ordinary machine.
While Person B reads this out loud: ( Person A don’t look! )
On October 8, 2005, twenty-three robotic vehicles lined up at the starting gate for the DARPA Grand Challenge. These were vehicles of all shapes and sizes, outfitted with special sensors and software to allow them to drive on their own, with no human operators. These would compete to travel more than 100 miles of rough desert terrain in order to win a $2 million prize.

4. Opening Activity Answer the following questions. Left column
What three defining capabilities of a robot were discussed in the left column?
In what order were the three discussed?
What sentence did not belong in that column?
Right column
What was the name of the event described in the right column?
What was special about the vehicles in this event?
What was the prize?

5. Opening Activity Multiple Inputs and Interference
Reading and listening are very difficult to do at the same time because both tasks demand the attention of the same area of the brain
Robots have a similar problem
Many sensors, only one program to watch them all
You might have tried switching back and forth quickly between reading and listening
This doesn’t tend to work very well for people
But it works fine for computers, because they can do it very quickly, and don’t forget what they had been doing before

6. Watching One Sensor How to watch a sensor
A Switch Block is set to watch the sensor, and based on what it sees, do different things
Example: Touch Sensor
Touch Sensor Switch checks value of sensor
Beep if pressed
Be silent if not pressed
Wait For Blocks, Sensor Blocks, and Loops are also used to check sensors, depending on how you want to use them
Beep if Pressed
Check the touch sensor; if it is pressed, make a sound… do nothing otherwise

7. Watching More Than One Sensor
“At the same time”
A robot can’t actually do more than one thing “at the same time”
It can do things in order so quickly that you can’t tell the difference
Therefore, you can’t technically watch more than one sensor “at the same time”
However, you can check several sensors in order so quickly you can’t tell the difference
Look and Listen
Check the Ultrasonic Sensor and the Sound Sensor one after another (use picture alerts instead of sounds so the Sound Sensor doesn’t get confused)

8. Multiple Sensors: Technical Review
The Sensors
Switches
Loops

9. Touch Sensor Detects physical contact Tells you: 1 if touched
0 if not touched
Poke, Poke?
The cross axle probe inserted into the end of the Touch Sensor contact increases its effective range

10. Sound Sensor Detects Sound Tells you: Amplitude (volume) of sound
Low numbers = quiet
High numbers = loud
Can be confused by sounds of different frequencies (pitch)
Listen Carefully
The Sound Sensor can detect many sounds, from gentle vibrations to jarring collisions

11. Light Sensor Detects light intensity Tells you:
The intensity of light detected
Low numbers = dark
High numbers = light
Light on the front can be turned on or off
Light the Way
The light sensor in Reflected Light mode shines its own light out and measures the amount that bounces back

12. Ultrasonic Sensor Detects distance Tells you:
Distance to a surface or object in front
Indicates a distance in cm or inches
Ro-Bat
The Ultrasonic Sensor uses the same basic principle for detecting distance as cave-dwelling bats do.

13. The Rotation Sensor is built into the Interactive Servo Motors
Detects rotation of the motor axle
Tells you:
Amount the axle has rotated in degrees or full rotations
Rotational position of an attached piece*
Linear position of an attached piece*
Rotato Chips
The Rotation Sensor is built into the Interactive Servo Motors
* If you also know the initial position and how the piece is attached, you can calculate this

14. Sensor Switch Block
Switch Blocks… allow the program to observe a value, and choose between different paths of code to follow, based on the observed value.
Sensor Switch Blocks… check a specified sensor to determine which group of blocks to run.
Keep Your Distance
Based on the value of the Ultrasonic Sensor, this Switch will either move backward (if the sensor value is less than the threshold), or move forward (if the sensor value exceeds the threshold)

15. Infinite Loop
The Loop Block runs the blocks inside it over and over again, until a certain stopping condition is met.
The infinite loop or “forever” loop has no stopping condition, and therefore will repeat the blocks inside over and over, forever.
Back and Forth
The loop causes the robot to repeat the forward-then-back motion forever

16. Summary
Humans and robots both have trouble paying attention to more than one input at a time
Robots can get around the problem by checking sensors quickly and repeatedly
Your sentry needs to watch more than just one sensor in order to detect many different kinds of hazards
In this Investigation, you will learn how to program the sentry to watch for multiple problems using different sensors “at the same time”