S5 ICT | The Internet of Things and Embedded Systems: Tutor Prep Guide (45-minute flow, script, common errors)

2026-11-15

Tutor lesson-prep guides · Secondary ICT

Students can say a fridge goes online, then cannot say how much data a month costs or how long a battery lasts. This lesson reduces IoT to three countables: samples, bytes and milliamps.

Objectives — By the end of the lesson students can: (1) explain that sensors input, a microcontroller decides and actuators output, with one example each; (2) get 600 samples from 10 Hz over 60 seconds and 1.2 KB at 2 bytes per sample; (3) get 20 hours from a 500 mAh battery at 25 mA, then an average of 0.99 mA at a 2 per cent duty cycle, about 505 hours or 21 days; (4) add 30, 150 and 20 milliseconds of latency to 200 milliseconds and name the hardest segment to shorten.

01 Prerequisites (3-minute check)

If any of these fails, fix it before the lesson starts.

Skill	Quick check	Pass mark
Multiplication and units	10 Hz sampling for 60 seconds: how many samples	600 samples
Byte conversion	How many kilobytes is 1,200 bytes	1.2 KB
Division	A 500 mAh battery at 25 mA lasts how long	20 hours
Percentages	What is 2 per cent of 25 mA	0.5 mA

02 Lesson flow (45 minutes)

Time	Stage	Tutor does	Student does
0-6 min	Entry check	Ask the sample count, 1,200 bytes, 500 over 25 and 2 per cent of 25; keep answers on the board	Spoken answers, working on paper
6-15 min	Act one: three roles, one loop	A sensor reads temperature, a microcontroller decides whether to start a fan, the fan is the actuator, then read again	Students describe the loop in their own example
15-25 min	Act two: the sampling rate sets the data volume	10 Hz is ten samples a second, so 600 in a minute; 2 bytes each gives 1.2 KB a minute and 1,728 KB a day	Students compute a month of data
25-35 min	Act three: the battery is division, the duty cycle is a weighted mean	500 over 25 gives 20 hours; two per cent working and 98 per cent asleep averages 0.99 mA for 505 hours, about 21 days	Students compute the average current and life
35-42 min	Question types: data, battery, latency, roles	The same chain with new numbers, four phrasings	Students do one and read out the unit
42-45 min	Exit check	Three spoken questions; note which act each error comes from	All three correct

03 Teaching script (read it out)

Scene 1: Act one: three roles, and sensing without acting is not control

An IoT device is not a sensor. A sensor only reads: temperature, light, humidity, motion. It produces a voltage, the microcontroller turns that voltage into a number and decides in software, for example switching a fan on above 28 degrees. Fans, lamps and locks are actuators, and they change the physical world. So the loop is read, decide, act, read again. Asked which part decides, the answer is the microcontroller; asked which part makes something happen, it is the actuator. An embedded system is those three on one small board doing one job, unlike a computer that runs whatever software you install.

Does a device with only a temperature sensor and no fan or lock count as a complete control system, and why not?

Scene 2: Act two: the sampling rate is a multiplication, not an adjective

A rate of 10 Hz means ten samples every second. Sample for 60 seconds and 10 times 60 gives 600 samples. At 2 bytes a sample the total is 1,200 bytes, or 1.2 KB. One minute is 1.2 KB, an hour is 72 KB, a day is 1,728 KB, roughly 1.7 MB, and a month is about 51.84 MB. So whether a data plan is needed depends first on the rate and the bytes per sample. Raise the rate to 100 Hz and every figure multiplies by ten, so a month becomes 518.4 MB and costs ten times as much. Higher is not better: one reading a minute is plenty for body temperature, while vibration needs 100 Hz.

If the device sampled every 5 seconds instead, what fraction of the monthly data would it use?

Scene 3: Act three: the battery is division, the duty cycle is a weighted mean

The easy version: 500 mAh at 25 mA gives 20 hours. Real devices sleep most of the time, working only 2 per cent of it. The 25 mA working current counts for 2 per cent, so 0.5 mA; the 0.5 mA sleep current counts for 98 per cent, so 0.49 mA; together the average is 0.99 mA. Divide 500 by 0.99 to get 505 hours, about 21 days. So one sleep mode takes the same battery from 20 hours to 21 days, a factor of 25. Latency comes last: 30 milliseconds from sensor to gateway, 150 from gateway to cloud and 20 for processing gives 200 milliseconds end to end. The hardest to shorten is the 150-millisecond cloud hop, which is why anything needing instant reaction, such as braking, keeps the decision local.

To cut total latency from 200 to 50 milliseconds, which segment must change, and why not the sensor?

04 Question types and worked steps

Type	Example	Steps	Answer
Classify the roles	A watering device with a soil moisture sensor, a microcontroller and a pump	Sensor reads, controller decides, actuator acts	The pump is an actuator and the sensor is the input
Data volume	10 Hz, 2 bytes a sample, 60 seconds	Rate times time gives samples, times bytes per sample	600 samples, 1,200 bytes or 1.2 KB
Battery life	500 mAh, 25 mA for 2 per cent of the time, 0.5 mA asleep	Compute the average current, then divide the capacity	Average 0.99 mA, about 505 hours or 21 days
Total latency	30 milliseconds sensing, 150 to the cloud, 20 processing	Add the segments and name the largest	200 milliseconds, the cloud hop is longest

Sanity check (teach this): Four checks: (1) a sample count is a whole number with no unit, so half a sample means the reasoning slipped; (2) converting bytes to kilobytes divides by 1,000 or 1,024, and the question states which, so never mix them; (3) an average current must sit between the sleep and working values, so 0.99 is sensible while anything above 25 is impossible; (4) hours must be divided by 24 to give days, and both units must not appear in one answer.

05 Independent practice (3 questions)

Question	Answer	What to watch
A sensor samples 10 times a second for 60 seconds: how many samples	600	Check the multiplication, not a division
600 samples at 2 bytes each: how many kilobytes	1,200 bytes, that is 1.2 KB	Ask for both units rather than the bare 1.2
A 500 mAh battery at an average 0.99 mA: how many days	505 hours, about 21 days	Check that hours are divided by 24

06 Common mistakes and what to say

Mistake	Student writes	Say this
Reading Hz as seconds per reading	Treating 10 Hz as one sample every 10 seconds, so 6 samples	Hz counts per second, so 10 Hz is ten per second and 60 seconds multiplies by 60 rather than dividing.
Mixing bytes and bits	Writing 1,200 bits as 1.2 KB	One byte is eight bits, so 1,200 bits is only 150 bytes, an eightfold error that ruins every data plan estimate.
Dividing capacity by the working current alone	Stopping at 500 over 25, so 20 hours	Only a device that never sleeps lasts 20 hours. With sleep the average comes first, otherwise the life is underestimated by 25 times.
Counting only the cloud hop	Answering 150 milliseconds and losing the sensing and processing	End to end adds every segment, and naming the longest matters because that is where improvement starts.

07 Homework (paper, section and question numbers)

S5 ICT Practice Paper 1, IoT and embedded systems section — Section B, questions 5 to 8

08 Exit check (last 5 minutes)

Question	Answer	Decision
10 Hz for 60 seconds: how many samples	600	Wrong: reteach act two, rate times time
500 mAh at an average 0.99 mA: how many days	About 21 days, that is 505 hours	Wrong: reteach act three, hours must be divided by 24
Latency of 30, 150 and 20 milliseconds: total	200 milliseconds	Wrong: reteach act three, end to end adds the segments

09 Tutor FAQ

Which year level is this for?

Hong Kong S5 ICT uses IoT as a context in the computer systems and networking unit, testing device composition and simple arithmetic. The S3 work on unit conversion and percentages is the prerequisite, so revise what KB and mA mean first.

Is 45 minutes enough?

Yes, provided act three gets ten minutes. The duty cycle is the most abstract step, so explain two per cent working twice and then write the weighted mean as one line.

Do students need real product specifications?

No. The numbers in the question are the whole story, and the four relationships are what count: samples are rate times time, bytes times eight give bits, the average current is weighted, and latency adds up.

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A TutorZone lesson-prep guide. Written by the TutorZone team; questions and lesson flow are original and are not taken from any school or publisher material.