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In this project, you’ll design and build a small house with an automatic nightlight.
During the day, the light stays off—but when it gets dark, the light turns on by itself!
You’ll explore basic electronics using a light-dependent resistor (LDR), and combine this with design and construction skills to make a practical and creative product.
You’ll learn how sensors work, how to solder components, and how to plan and build a housing that looks great and works well.
Parts Required
Parts Required
This Template
5mm adhesive copper tape
Components:
LDR
47k or 100k resistor (47k can be problematic)
CR2032 x 2 batteries
CR2032 twin battery holder
BC547 Transistor
LED (standard 5mm coloured - note: green can be problematic)
Glue (hot melt is best)
Colouring pencils / crayons / spare card
Safety First
Safety First
Before we get building, here are some important safety rules:
💧 Burns – what to do
Know where the nearest running water is. If you burn yourself, go straight there—no need to ask first.
If it’s a bad burn (very rare!), we’ll head to the school nurse.
🚨 Fire safety
Soldering + cardboard = smoke. Be smart. No one wants to test the smoke alarm.
🔥 Soldering irons
Only two places for a hot soldering iron:
In your hand (when you’re soldering), or
In the holder. Never leave it on the bench. Ever.
💸 Don't waste solder
Solder is expensive. Don’t melt it into puddles. Don’t melt anything else either.
🦺 Wear safety glasses
Always wear safety glasses when soldering, trimming component legs, or if you’re near someone doing it. Your eyes are squishy. Parents prefer them to stay squishy and intact.
If you wear glasses, use safety goggles over them—solder can melt plastic lenses, and that’s not fun (or cheap) to fix.
Step 1: Laying down Copper Tape
Step 1: Laying down Copper Tape
Fix Copper Tape on Green Lines
Stick the copper tape along the marked lines on your template.
Always overlap the ends of the tape – don’t just line them up edge-to-edge.
If a piece is cut too short, overlap the new piece so it connects properly.
Press the Tape Firmly
Use the back of your fingernail or another smooth tool to press the tape down flat.
This makes sure it sticks well and carries electricity properly.
Solder Every Joint
Even if the tape overlaps, you must solder the joints.
The sticky layer on the tape can stop electricity from flowing unless solder is added.
Use the Correct Soldering Technique
Place a small amount of solder on the joint.
Hold the side of the soldering iron tip on top of the solder until it melts.
Move the tip in a small circle to make a neat, shiny “puddle.”
This should only take a couple of seconds per joint.
If you heat it for too long, the tape can burn or lift off.
Avoid “Seagull Poop” Soldering
Do not poke the soldering iron up and down like a sewing machine.
This makes messy, weak joints.
Instead, keep the tip still and swirl gently.
Do Not Fold the Template Yet
Keep the template flat until you are ready to glue it at the very end.
Folding it too soon can crack the copper tape and cause connection problems.
Step 2: Adding the Resistor
Step 2: Adding the Resistor
Choose the Correct Resistor
Start with a 100kΩ resistor (standard choice).
You can try a 47kΩ resistor later if you want the LED to be brighter.
Sometimes, 47kΩ can make the LED turn on too early. You can swap it at the end to test this.
Learn the Resistor Colour Code
Use a resistor colour chart (handout or online) to check what value your resistor is.
Understand that:
k = kilo = 1,000 (three zeros)
M = mega = 1,000,000 (six zeros)
Example: 47kΩ = 47,000 ohms.
Check the tolerance band (e.g., brown = ±1%).
A 47kΩ ±1% resistor should measure between 46,530Ω and 47,470Ω.
3. Prepare the Resistor for Mounting
Bend the legs slightly so the resistor lies flat on the card.
Trim the extra length off both ends into the bin (so the pieces don’t end up in the carpet or someone’s shoe).
4. Confirm the Value of Your Resistor
Read the colour bands and write down the value.
Use a multimeter to measure the resistance:
Hold the probes on the resistor legs.
Note the actual value and write it beside your resistor on your template.
Bonus Tasks
Bonus Tasks
Bonus activity: measure your own body resistance between two hands.
This shows why electricity can flow through you if the voltage is high enough.
Keep hands away from the circuit when testing – your body can change the reading.
Understand Tolerances and Real-World Factors
Notice if your resistor isn’t exactly the printed value.
Discuss why resistors vary (manufacturing, cheap parts, temperature).
Learn that some circuits need precise parts, but in this simple circuit, small differences are fine.
Optional Extension Task
Practice calculating:
The value of resistors from their colour bands.
The colour bands needed for specific resistor values.
You can do this now or save it for extra practice.
Step 3: Adding the LDR
Step 3: Adding the LDR
An LDR is a special resistor that changes its resistance depending on how much light hits it.
Bright light → low resistance → electricity flows easily.
Darkness → high resistance → electricity flows less easily.
You can think of it like a light-controlled tap for electricity — more light means the tap opens wider.
Mount the LDR
Poke two holes in the card with a compass or something similar
(if the laser cutter didn’t do it already),Feed the LDR in from the back (plain) side,
Bend the legs down flat, trimming them off to length.
Tin the ends of the legs and copper tape.
Then solder them down.
Top
Bottom
6. Now draw a table in the blank square of the template. This table will be the basis for the next few lessons of work.
Calibrating the LDR
Calibrating the LDR
Measure in room light:
Put the multimeter probes on the copper tape further down the template.
Ask a partner to curl the template so the head of the LDR is facing the room.
Read the resistance and write it in your table. Include the units (Ω, kΩ, or MΩ) — a number without units is meaningless!
Measure in darkness:
Cover the LDR completely with a pencil case or book so no light gets in.
Read and record the resistance.
Measure in bright light:
Shine a phone torch directly under the head of the LDR.
Read and record the resistance.
Checking the fixed resistor (100 kΩ)
Look at the tolerance band on the resistor.
Gold = ±5% → could be between 95 kΩ and 105 kΩ and still be correct.
Brown = ±1% → could be between 99 kΩ and 101 kΩ.
Compare your measured value to the tolerance range.
Cheap resistors (e.g. bulk packs from AliExpress) might be slightly off — that’s fine for a simple circuit like this.
Step 4: Voltage Divider
Step 4: Voltage Divider
A voltage divider is a simple way to take a bigger voltage and make it smaller.
Think of it like turning down the volume on a speaker – you don’t want the full blast, just a lower level.
Everyday Examples of Voltage Dividers
Arduino vs. Raspberry Pi (classic electronics example):
The Arduino runs at 5V, but the Raspberry Pi only handles 3.3V. If you connect 5V straight to the Pi, it can break. A voltage divider “steps down” the voltage to a safe level.Turning down a garden hose (analogy):
Imagine a garden hose with too much water pressure. You partly close the tap to reduce the flow. A voltage divider does the same with electricity – it reduces the voltage.Using the right charger for a phone:
A phone needs 5V to charge. If you plug it into 12V, it will fry! Inside chargers there are circuits (like voltage dividers and regulators) that bring the voltage down to the safe level.Night-light sensor (your project):
An LDR changes resistance with light. In bright light, the divider output is low (so the lamp stays off). In the dark, the divider output is high (so the lamp switches on).
Volume knob on a speaker:
A volume control is really just a type of voltage divider. Turning the knob changes the resistance and lowers the signal going to the speaker, so the sound is softer.
The Voltage Divider in Our Circuit
In this circuit we are using a voltage divider made from:
a 100kΩ resistor (fixed)
an LDR (light dependent resistor)
The battery voltage goes across both of them. The output voltage comes from the middle, between the two parts.
⚡ Important: This output voltage is not fixed. It changes depending on the light level, because the LDR’s resistance changes with light.
Add the Battery Pack
Solder the battery pack in place. Don’t cut the wires short – leave them long enough so the pack can be mounted later.
Put the batteries in.
You should measure about 6V (or 6.4V with new batteries).
If you see –6V, both batteries are backwards.
If you see 0V, one battery is backwards, or the switch is off.
Very occasionally, the battery pack itself can be faulty.
👉 Always check with a multimeter in DC mode to make sure you’ve got the right voltage before going further.
Step-by-step: Measure → Calculate → Test
Step-by-step: Measure → Calculate → Test
Goal: Work out and check the voltage from our voltage divider (100 kΩ resistor = R2, LDR = R1) in three light levels: bright, room, dark.
Use the formula:
Measure the battery voltage
Set your multimeter to DC volts (V⎓), use an appropriate range.
Turn the battery pack ON.
Red probe to the battery +, black probe to – (0 V).
Read the value (about 6.0–6.4 V if new).
If the reading is negative, swap the probes.
If it’s 0 V, check a battery is not backwards and the switch is on.
Record 𝑉𝑖𝑛 in volts (V) in your table.
Calculate Vout for each light level
Do each calculation on paper in these steps:
First: S=R1+R2
Divide: F=R2÷S
Multiply: Vout=Vin×F
Write the unit: volts (V). If it’s very small, also write in mV.
Worked example (Bright):
Given Vin=6.4 V, R1=98,300 Ω, R2=86 Ω,
S=98,300+86=98,386 Ω
F=86÷98,386≈0.00087
Vout=6.4×0.00087≈0.0056 V=5.6 mV
Repeat for Room and Dark using your R2 values.
Measure the actual Vout
Keep the meter on DC volts (20 V).
Black probe to circuit 0 V (–).
Red probe to the middle node between the 100 kΩ and the LDR.
Measure VoutV_{out}Vout in Bright, Room, and Dark.
Record the readings (note the unit—your meter may show mV).
Quick “does this make sense?” check
This is a night-light: in bright light we expect low Vout (lamp off).
In the dark we expect higher Vout (lamp on).
If your numbers follow that pattern, they’re likely sensible.
Step 5: Adding Transistor
Step 5: Adding Transistor
🧠 What’s Happening So Far?
Your voltage divider gives:
Almost 0V in bright light
A small voltage (e.g. 300–600mV) in room light
Close to full battery voltage in the dark
Your night light should turn on in the dark, so these voltage changes make sense. That’s called a "sanity check"—does the result match what you expect?
❓ But Why Won’t the LED Light Up Yet?
An LED needs 2.5–3V to turn on—but also needs enough current.
The voltage divider gives enough voltage, but not enough current to power the LED.
You need a switch to help – something that uses the small signal to control a bigger one.
⚡ Enter: The Transistor!
A transistor is like a magic switch.
The small signal from your voltage divider goes into the transistor and lets more current flow to the LED.
It's like your finger on a light switch – small effort, big result.
✅ Step-by-Step Instructions
✅ Step-by-Step Instructions
1️⃣ Learn What a Transistor Does
A transistor can do two things:
Amplify (like sound in a speaker)
Switch (like a light switch)
In this project, we use it as a switch.
2️⃣ Identify the Pins
The transistor we use is a BC547.
It has three pins:
Collector (C) – high power in
Base (B) – control pin
Emitter (E) – Connected to ground to provide current through the LED
Check the diagram on the right to ensure you know which pin is which.
3️⃣ Work Out How It Fits
The template does have the pins labelled—Make sure you connect the transistor the right way around!
Look at your transistor and compare with the circuit diagram or pinout.
Turn the transistor the right way so each leg lines up with the right trace.
If unsure, ask your teacher to check before soldering.
4️⃣ Solder It On Carefully
Lay the transistor flat against the card.
Solder each pin where it touches the copper tape.
Laying it flat helps prevent damage if it gets bumped later.
🧪 Bonus Learning (Optional)
Use the light switch analogy:
Your finger = base pin (low-power control)
Switch contacts = collector & emitter (high-power path to the LED)
Discuss how transistors control large currents with small ones – like your night light needs.
Step 6: Add LED
Step 6: Add LED
✨ What’s an LED?
LED = Light Emitting Diode.
It only works in one direction – so it matters which way around you place it.
✅ Step-by-Step Instructions
✅ Step-by-Step Instructions
1️⃣ Choose Your LED Colour
Pick a colour you like!
Red, orange, yellow, or blue work well.
⚠️ Avoid green – it sometimes blows in this circuit.
2️⃣ Identify the LED Legs
Cathode (–) = negative leg
Shorter leg
Flat edge on the plastic side
Cup shape inside the LED
Anode (+) = positive leg
Longer leg
3️⃣ Trim the Legs Carefully
Bend the legs carefully with a plier
Cut the legs shorter so they don’t touch other tracks.
If the leg touches the wrong part (like the base track), it can short the circuit and damage your LED or transistor.
4️⃣ Place It in the Circuit
Match the short leg (–) to the negative side of the circuit.
The long leg (+) should connect to the positive output from the transistor.
5️⃣ Solder the LED In Place
Double-check the direction!
Pre-tin copper and LED legs
Solder the LED legs to the copper tape securely.
Step 7: Test the Circuit
Step 7: Test the Circuit
Test the Circuit
Try it out!
Cover the light sensor to make the LED turn on.
If it doesn’t work:
Check LED direction
Check for short circuits (legs touching the wrong parts)
Ask your teacher to help troubleshoot
Not Working!
Not Working!
Faults to look for
Component legs not trimmed, so extending into other parts of the circuit
Copper track not properly joined with solder puddles
Transistor around the wrong way
Battery orientation in the holder wrong, or no batteries fitted at all.
LED around the wrong way - or possibly blown up
Broken track - particularly beside the door at the fold line - these can be fixed with solder normally - or worst case, a new copper tape bridge soldered in. These breaks often happen at the fold lines, particularly if a student has not listened, and folded their template prematurely, meaning the copper flexes a lot more at that point than it can handle.
Step 8: Completing the House
Step 8: Completing the House
Glue-Up
Glue-Up
1️⃣ Set Up Your Workspace
Choose a glue station – there should be 3–4 glue guns available.
Make sure your circuit is working before you start folding.
2️⃣ Add a Tiny Dot of Glue to Each Tab
Use only a small dot of glue—that’s all you need.
Too much glue makes it hard to fix mistakes later.
3️⃣ Glue One Wall and Half the Roof First
Start with just one wall and half of the roof.
Press gently and let it set.
4️⃣ Test the Circuit Again
Important! After gluing one wall and half the roof, test your circuit.
Folding the copper tape can sometimes cause cracks—you want to catch this early!
5️⃣ Continue Gluing If It Still Works
If the LED still works, continue gluing the rest of the walls and roof.
Keep using tiny dots of glue.
6️⃣ Fixing a Broken Track (If Needed)
If the circuit stops working, tell your teacher.
It’s easier to fix now while most of the housing is still open.
7️⃣ If You Need to Fix It Later
Don’t worry!
The small glue dots make it easier to cut the joints open with a Stanley knife if needed.
Decoration and Marking - Bringing Your Night Light to Life
Decoration and Marking - Bringing Your Night Light to Life
This is your chance to be creative, have fun, and show pride in your work. Make it personal, detailed, and something you’re proud to show off.
🎨 1️⃣ Gather Your Materials
Use:
Colouring pencils or pens
Extra card or paper
Glue guns (shared at the glue station)
🏠 2️⃣ Add Decorative Details
Think about what makes a house feel real or interesting. Add things like:
Window boxes or flower pots
A front yard, garage, or fence
Curtains or chimney
Roof tiles, door handles, paths, mailboxes
🌈 3️⃣ Colour It Nicely
Take your time! Use shading, patterns, or bold colour to make it stand out.
Be neat – attention to detail shows pride in your work.
🧠 4️⃣ Create a Backstory (Optional but Fun!)
Imagine this is a real house:
Who built it?
Who lived in it?
What happened there over the years?
You can write this on the back or on a small name card if you like.
📝 5️⃣ Self-Marking Time
After decorating, think about how well you’ve done:
Did you add nice details?
Did you take care and pride in how you decorated it?
What would YOU give your prject out of 10 for effort and creativity?
🧑🏫 6️⃣ Final Marking
Your teacher will mark your project generously based on:
Attention to detail
Pride in your work
Creativity and effort
✅ Bonus: Most students will get an "Excellence" just for completing their project and putting in solid effort.
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