Week 4: Helping Robots Sense

Session length: 70-85 minutes

Learning purpose

Now that the robot moves and follows instructions, students give it senses. They meet touch, distance, light, and color sensors and learn that a sensor reading is a number the robot can measure. They discover that a threshold is a cutoff that turns numbers into 'near or far' and 'light or dark', that every sensor has detection limits, and that readings wobble a little (noise), so you take several and calibrate them for this room and this robot. After reading and calibrating, they program one sensor-based stop - the robot drives and uses its distance sensor to halt right before a wall - so a threshold finally controls a real action. Fuller automatic behavior with loops and conditions across a whole mission comes next week.

Expected student outcomes

By the end of this week, students can:

Name the touch, distance, light, and color sensors and what each one measures
Read a sensor value and explain that a reading is a number, not a yes/no
Find a threshold that separates near from far or light from dark
Explain detection limits, noise, and why you take several readings
Calibrate a sensor so its readings are reliable for this room and robot

Suggested pacing

About 70-85 minutes. Adjust to your group - these are guides, not limits.

Step	Focus	Minutes
Four senses and what a reading is	Touch, distance, light, and color sensors; a reading is a number, not a yes/no.	15 min
Predict the readings	Guess how a reading changes with distance, and whether a still wall gives the same number twice.	5 min
Sensor Investigation Lab	Read a sensor across conditions and find a threshold.	18 min
Calibration & Threshold Challenge	Handle noise, then calibrate a reliable threshold for this room.	12 min
Sensor-based stopping challenge	Program the robot to drive and use the distance sensor to stop before the wall; run three trials and tune the threshold.	15 min
Knowledge check	Five questions on readings, thresholds, noise, and calibration.	8 min
Reflection	Write about thresholds, noise, and why calibration matters.	7 min

Before you start

Set up

Print the Sensor Reading Log for each student or pair.
Set up a measured spot with a tape measure marked at 10, 20, 40, and 80 cm and a wall or box to place there.
If using kits, attach a sensor and pre-load a short read-and-report program; if using the simulator, open it on each device; for unplugged, prepare a blindfold and a set of light/dark cards.

Prepare ahead

Try the sensor lab yourself first so you know the real readings and detection limits of your sensor.
Take five readings of a still object ahead of time so you can show students what noise looks like.
Decide the two clear conditions (dark vs light, or near vs far) you'll use for the calibration challenge.

Materials

Sensor Reading Log worksheet (printable)(Kit, Simulator, Unplugged)
Tape measure or ruler for setting known distances(Kit, Simulator, Unplugged)
Pencil and paper for recording readings(Kit, Simulator, Unplugged)
A programmable robot with a touch, distance, light, or color sensor(Kit)
A wall, book, or box to place at measured distances(Kit)
A flashlight and colored cards for light and color testsOptional(Kit)
Computer or tablet with the browser simulator(Simulator)
A blindfold or scarf for the human-sensor activity(Unplugged)
Cards in light and dark shades (or gray-scale strips) to sort(Unplugged)

Safety

cautionKeep the robot on a stable surface and mind the wheels when moving it between test spots.(Kit)
cautionGuide any blindfolded 'human sensor' and clear the floor so no one trips.(Unplugged)
cautionDon't shine a flashlight directly into anyone's eyes when testing light sensors.(Kit)
infoSave your reading log often so a browser refresh doesn't lose your data.(Simulator)

Full safety briefing

Review these once with your group. They apply across the whole course; the notes above are what matters most this week.

Batteries and circuitsKit

Use only appropriate low-voltage educational equipment - no wall outlets and no household batteries wired by hand.
Never connect a battery's two terminals directly to each other.
Stop right away if a motor, wire, or battery becomes hot, and tell an adult.
Disconnect the power before changing wheels, motors, or other mechanical parts.

Motors and gearsKit

Keep fingers, hair, jewelry, sleeves, and loose clothing away from moving gears and wheels.
Do not force a stalled motor that has stopped turning - switch it off and find out why.
Make sure moving parts are secured before you run a test.

Moving robots

Test on the floor, not on a table where the robot could drive off an edge.
Keep robots away from stairs, roads, water, pets, and people's feet.
Use a clear, open test area.
Always include a safe-stop behavior so the robot halts when the job is done or something is in the way.

Tools and materialsKit, Unplugged

Ask an adult for help with cutting or any sharp tools.
Use safe classroom materials - no sharp, toxic, or breakable items.
Never launch or swing an attachment toward a person.

Running the session

1.Start with the four sensors and the big idea that a reading is a number, not a yes/no, before any measuring.
2.Have students predict readings first, then run the Sensor Investigation Lab and record every value.
3.Stress that this week the robot only reads and reports - students, not the robot, decide what the numbers mean; automatic reactions come next week.
4.Run the Calibration & Threshold Challenge, showing noise with repeated readings and setting the threshold between two clear conditions.

Common misconceptions

'A sensor gives a yes or no' - most give a number that changes smoothly with the world.
'One reading is enough' - noise means you should take several and use the middle or average.
'The same threshold works everywhere' - light and surfaces change by room, so you calibrate for where you are.
'The sensor is broken because the number wobbles' - small wobble is normal noise, not a fault.

Questions to ask

What number did you read, and what does it mean - near or far, light or dark?
Why did you take more than one reading at the same spot?
Where did you set your threshold, and how did you decide?
Would your threshold still work in a brighter room? How would you check?

Classroom & group adaptations

Make it easier

Use only one sensor and two clear conditions (a near wall and a far wall), and set the threshold together as a group.

Make it harder

Have students compare two sensors, quantify the noise as a range, and calibrate a threshold that works across two different rooms.

Groups & whole class

In pairs or small groups, give each student a role that rotates - driver (builds or types), navigator (reads the plan), and recorder (fills the worksheet) - so everyone participates. For a whole-class demo, run one shared robot or simulator on the board, have students predict together, then let groups repeat it on their own path. Groups can also mix paths: one builds on the kit while another checks the same idea in the simulator or unplugged, then they compare results.

Hardware and no-hardware notes

Every activity this week runs three ways - all three teach the same core idea, so pick whichever fits your room. No specific product is required.

Kit

Sensor Reading Log worksheet (printable)
Tape measure or ruler for setting known distances
Pencil and paper for recording readings
A programmable robot with a touch, distance, light, or color sensor
A wall, book, or box to place at measured distances
A flashlight and colored cards for light and color tests

Simulator

Sensor Reading Log worksheet (printable)
Tape measure or ruler for setting known distances
Pencil and paper for recording readings
Computer or tablet with the browser simulator

Unplugged

Sensor Reading Log worksheet (printable)
Tape measure or ruler for setting known distances
Pencil and paper for recording readings
A blindfold or scarf for the human-sensor activity
Cards in light and dark shades (or gray-scale strips) to sort

Troubleshooting

Common problems from this week's activities and what to try.

The reading jumps around and won't settleKitTry: That is noise - take three readings at each distance and use the middle one.
The distance reading is stuck at a big number no matter whatKitTry: You may be past the sensor's detection limit or aimed at nothing; point it straight at a flat wall within about 1 meter.
The sim reading changes by a little each time even when the robot is stillSimulatorTry: That is simulated noise on purpose - take a few readings and use the middle value.
Not sure which number on screen is the sensorSimulatorTry: Match the read-out that changes when you move the wall closer - that is the distance value.
Two students give different numbers for the same cardUnpluggedTry: That is like noise between sensors - agree on a shared scale and re-read, which is a kind of calibration.
Everything gets the same numberUnpluggedTry: Spread the conditions further apart (a much closer wall, a much darker card) so the readings clearly differ.
A surface sometimes lands on the wrong sideKitTry: The two conditions may be too close together, or noise is large; move the threshold or use more contrasting surfaces.
The whole set of readings shifted since earlierKitTry: The room light changed - re-calibrate now, which is exactly why calibration matters.
Tiles keep sorting wrong even after setting a middle thresholdSimulatorTry: Raise the contrast between tiles or turn the simulated noise down, then re-calibrate.
The average is hard to computeSimulatorTry: Add the three readings and divide by three, or just use the middle reading of the three.
Two people set different thresholdsUnpluggedTry: That is why calibration matters - agree on one shared scale and threshold for the group.
The middle cards are hard to sortUnpluggedTry: Middle values are near the threshold; that is normal, note them as the hardest cases.

Knowledge-check answer key

Answers are shown here for the adult only - the student worksheet keeps them hidden.

1. Match each sensor to what it measures.
Correct answer: Distance sensor -> How far away something is; Light sensor -> How bright it is; Touch sensor -> Whether something is pressed; Color sensor -> What color a surface is
Why: Each sensor measures one thing: distance, light level, touch, or color.
2. In your own words, what is a sensor threshold?
Correct answer: A threshold is a cutoff number. If the reading is on one side of it the robot decides one thing, and on the other side it decides another - like 'closer than 15 cm means a wall is near.'
Why: A threshold is a cutoff value that turns a sensor number into a yes/no decision.
3. What is a sensor reading?
Correct answer: The number a sensor gives you at one moment
Why: A sensor reading is the number a sensor reports at one moment, and it changes smoothly as the world changes.
4. A distance sensor reads 30 cm at one wall and 12 cm at a closer wall. What does this tell you about how the reading works?
Correct answer: The reading gets smaller as things get closer
Why: A distance sensor's reading shrinks as the object gets closer, which is how you can turn it into a near/far decision.
5. You want the robot to treat anything closer than 15 cm as 'near'. What is the number 15 called?
Correct answer: A threshold
Why: A threshold is a cutoff value you choose that separates two cases, like near versus far or light versus dark.
6. You read the same still wall five times and get 30, 31, 30, 29, 31. Why do the numbers wobble?
Correct answer: Because of noise, so you take several readings
Why: Noise is the small, normal wobble in readings even when nothing changes, so roboticists take several readings and use the middle or average.
7. Your light-or-dark threshold worked in the classroom but fails in a sunny room. What should you do?
Correct answer: Calibrate the sensor for the new room and set a new threshold
Why: The same threshold won't work in every room, so you calibrate the sensor to the new light and choose a new threshold that reliably separates light from dark.