Worksheet

Room Codes for the Delivery Robot: Voltage Levels or Pulses?

Grade 8 practice: a robotics team's delivery robot decodes room numbers, uses a check pulse and runs hallway noise tests that show why digital signals are more reliable.

Grade 8ScienceInteractive · Printable

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1 NGSS standard
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11 questions
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Details

Format: Interactive · Printable
Grade: Grade 8
Subject: Science
Question types: Fill in the blank, Multiple choice, Circle the answer, Short answer

About this worksheet

What students practice

Students decode digital pulses using a threshold and explain why small noise does not change them.
Students use a check pulse to tell when a digital code was damaged on the way.
Students use test data to argue that digital signals carry information more reliably than analog signals.

How to use

Work through the room 9 examples in paragraphs 2 to 4 together before students start. Part 1 practices the codes; Part 2 uses the test data.

Curriculum

NGSS standard covered

MS-PS4-3

Explain why digital signals carry information more reliably than analog signals.

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Room Codes for the Delivery Robot: Voltage Levels or Pulses?

Decode a robot's room codes and use hallway test data to compare analog and digital signals.

Part 1: Two ways to send a room number

Read the team's notes, then use them to answer the questions.

Team Notes: Teaching the Robot Where to Go

1The robotics team at Hollow Creek Middle School is building a delivery robot for the school. It will carry printer paper, notes and lost-and-found items from the main office to 15 rooms, numbered 1 to 15. For each delivery, the office computer sends the room number to the robot by radio, and the robot's receiver turns the radio signal into a voltage. Team members Ximena Achebe and Pavel Lindqvist soon found a problem. Motors in the building, such as the cafeteria freezers, the gym's big ceiling fans and the elevator motor, add electrical noise: random extra voltage, up or down, on top of the voltage in the receiver. The team built two versions of the robot's code and tested both.

2In the analog version, the office sends a voltage of 0.5 V for each room number, so room 1 is 0.5 V, room 9 is 4.5 V and room 15 is 7.5 V. The robot measures the voltage that arrives and drives to the room whose voltage is closest to it.

3In the digital version, the office sends the room number as four pulses. Each pulse is 0 V, which stands for 0, or 5 V, which stands for 1. The robot reads any pulse of 2.5 V or more as a 1 and any pulse below 2.5 V as a 0. The four pulses stand for 8, 4, 2 and 1, in that order, and the robot adds up the values of the pulses that are 1. Room 9 is sent as 1, 0, 0, 1, because 8 + 1 = 9.

4Coach Rosalind Okafor showed the team one more trick, a check pulse. After the four room pulses, the office sends a fifth pulse, chosen so that the total number of 1s in all five pulses is even. Room 9 already has two 1s, so its check pulse is 0, and the full code is 1, 0, 0, 1, 0. The robot counts the 1s it receives in all five pulses. If the count is odd, it knows that noise changed a pulse, so it asks the office to send the code again. This is called a resend.

5To test both versions, the team chose four places along the robot's route. In each place, they measured the largest noise voltage with a meter, then sent 20 room codes with each version and counted how often the robot chose the right room. For the digital version, they also counted the resends. Every resent code arrived without damage.

Use paragraph 2. The office sends room 9 the analog way, as 4.5 V. In the gym hallway, noise adds 0.4 V to the signal.

The robot drives to room .

Use paragraphs 3 and 4. Near the elevator, the robot receives these five pulses, in order: 4.6 V, 0.8 V, 3.1 V, 2.2 V, 0.3 V. The count of 1s is even, so the robot accepts the code.

The robot drives to room .

The office sends room 9 the digital way: 5 V, 0 V, 0 V, 5 V and a check pulse of 0 V. In the gym hallway, noise adds 0.4 V to every pulse. What does the robot do?

A. It drives to room 9, because each pulse stays on the same side of 2.5 V as before.
B. It asks for a resend, because the pulses did not arrive at exactly 0 V and 5 V.
C. It drives to room 13, because the noise turned the 4 pulse from a 0 into a 1.
D. It drives to room 10, because the pulses arrived 0.4 V higher than they were sent.

Use paragraphs 3 and 4. Room 7 is sent as 0, 1, 1, 1 before the check pulse. Write 0 or 1.

The check pulse for room 7 is .

Each code below shows the five pulses as the robot read them. Circle every code that the robot would reject and ask the office to resend.

1, 0, 0, 1, 00, 1, 1, 0, 11, 1, 1, 1, 00, 0, 1, 0, 01, 0, 1, 1, 1

Part 2: The hallway test

Use paragraph 5 and the test table to answer the questions. The right-room counts show the final result after any resends.

Hallway Test: 20 Codes With Each Version in Each Place
Place	Largest noise (V)	Analog: right room	Digital: right room	Digital: resends
Library hallway	0.1	20	20	0
Cafeteria hallway	0.3	14	20	0
Gym hallway	0.6	5	20	0
Next to the elevator	3	1	19	5

Use the test table. Look at the gym hallway.

The analog version sent the robot to the right room for % of the codes there.

Which statement best describes the first three rows of the test table?

A. As the largest noise grew from 0.1 V to 0.6 V, both versions got fewer rooms right, but the digital version dropped more slowly.
B. As the largest noise grew from 0.1 V to 0.6 V, the analog version got fewer rooms right, while the digital version got all 20 right.
C. As the largest noise grew from 0.1 V to 0.6 V, the analog version stayed at 20 rooms right, while the digital version dropped to 5.
D. As the largest noise grew from 0.1 V to 0.6 V, the analog version got more rooms right, while the digital version needed more resends.

Next to the elevator, the digital version needed 5 resends and sent the robot to the wrong room once. Which explanation fits paragraphs 3 and 4 best?

A. The check pulse caught the changed codes, but the office typed in the wrong room number once.
B. Noise there raised the pulses by the same amount, so the robot read the codes as higher room numbers.
C. Noise over 2.5 V flipped some pulses; one flip made the count odd, but in one code two flips kept it even.
D. The elevator's 3.0 V noise was too small to change a pulse, so the wrong room came from a weak robot battery.

The team wants to stop wrong deliveries next to the elevator. Which change would most likely help?

A. Read any pulse above 1.0 V as a 1 instead of using 2.5 V.
B. Send each code twice and act only if both copies match.
C. Drop the check pulse so that each code is quicker to send.
D. Switch to the analog version whenever it is near the elevator.

10.

Use the test table. Think about all 80 codes sent with the analog version in the four places.

Of all 80 analog codes, % sent the robot to the right room.

11.

Pavel says, "Let's keep the analog version. It was perfect in the library hallway, and that hallway is quiet." The robot's route from the office passes the cafeteria, the gym hallway and the elevator. Which version should the team use? Write a claim, give evidence from the test table, and explain your reasoning using what noise does to each kind of signal.