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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
1. Choose the Resistor
Start with a 100 kΩ resistor. You can try a 47 kΩ resistor later to see how it changes when the nightlight turns on and how brightly the LED glows. If it turns on too early, change back to 100 kΩ.
2. Check the colour bands
Use a resistor colour chart to identify the value. Your resistor may have four or five bands, so check which type you have.
k means kilo, or 1,000. For example, 47 kΩ = 47,000 Ω.
M means mega, or 1,000,000.
The final band shows the tolerance. Gold means ±5%; brown means ±1%.
3. Measure and record the resistance
Do this before bending or cutting the leads. Check the colour bands, even if the resistor came from a labelled container. Then hold the multimeter probes against the two leads and record the actual reading, including the number, prefix and unit. For example: 99.6 kΩ.
4.Bend, Trim and Solder
Bend the leads as shown in the diagram so the resistor lies flat on the card, with one lead resting on each separate copper foil strip. Leave enough lead on the foil for a solder joint. Trim only the excess with side cutters, catching the offcuts in the bin.
Tin each lead: Heat the part of the lead that will touch the copper foil, then feed in a small amount of solder so it coats the lead.
Add solder to each foil strip: Place the soldering iron tip on the copper foil where the lead will go. Use the 3–3–3 sequence: heat the area for about 3 seconds, feed in solder for about 3 seconds, then remove the solder wire while keeping the iron in place for about 3 seconds. Remove the iron and let the solder cool.
Place each tinned lead on its prepared foil strip. Heat the lead and solder on the foil until they join, then remove the iron and let the joint cool without moving it. Keep the two foil strips separate.
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.
An LDR responds to light: When more light reaches its sensing face, its resistance decreases. When the light is blocked, its resistance increases.
You can think of it like a light-controlled tap for electricity — more light means the tap opens wider.
Draw your results table
In the blank square on your template, use a pencil and ruler to copy the table shown. You will use it again when you study the voltage divider. For now, fill in only the “LDR Resistance” column. Include the number, prefix and unit with every reading, such as 8.2 kΩ.
Measure the LDR in three light conditions
Measure the LDR in three light conditions
Set the multimeter to resistance (Ω). Touch one probe to each LDR lead. You may hold one lead steady with a finger, but do not touch both leads at once—your body could affect the reading.
Room light: Leave the sensing face uncovered. Record the resistance in the Room row.
Darkness: Cover the sensing face completely. Record the resistance in the Dark row.
Bright light: Shine a torch onto the sensing face. Record the resistance in the Bright row.
Include the number, prefix and unit in each reading (Ω, kΩ or MΩ).
The resistance should be highest in darkness and lowest in bright light.
Note: If your multimeter has manual ranges, start on a high resistance range and move down until you get a clear reading.
If the display shows OL or 1, select a higher range.
An auto-ranging meter selects the range for you; wait for the reading to settle. Check whether the display says Ω, kΩ or MΩ before recording the value.
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 as shown below.
Tin the ends of the legs and copper tape before soldering it together.
Then solder them down.
Top
Bottom
Step 4: Redict and Test Voltage Divider
Step 4: Redict and Test Voltage Divider
A voltage divider uses two resistances to produce a voltage that is lower than the battery voltage. The output is measured at the point between them.
Your night-light has a fixed resistor and an LDR. They share the battery voltage. When the light level changes, the LDR’s resistance changes, so the voltage across it changes too.
Bright light: the LDR’s resistance is low, so the voltage across it should be low.
Darkness: the LDR’s resistance is high, so the voltage across it should be higher.
You have already measured your fixed resistor and your LDR in bright light, room light, and darkness. Find those readings from Steps 2 and 3—you’ll use them shortly.
⚡ 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 Holder
If you have not attached your battery holder yet, solder its wires to the correct points on the circuit. Leave the wires long enough to mount the holder inside your house later. Insert the batteries and turn the holder’s switch on.
Measure your battery voltage
Set the multimeter to DC voltage (V⎓).
Turn the battery pack ON.
Put the red probe on battery + and the black probe on battery −.
Record the reading as Vin. Two new CR2032 batteries should measure around 6.0 to 6.3V together. If the reading has a minus sign, first check that the probes are on the correct points. If the reading is close to zero, check the switch, batteries and connections.
Write this in the battery holder outline on your template. Remember the unit (V) as well.
Calculate the expected voltage across the LDR
Calculate the expected voltage across the LDR
Use the values you already recorded for your fixed resistor and LDR, along with your measured battery voltage:
Use the same unit for both resistance values. For example, if you use kΩ for the fixed resistor, convert your LDR reading to kΩ too.
Worked example: The battery measures 6.2 V. The fixed resistor measures 98 kΩ, and the LDR measures 2 kΩ in bright light.
Now calculate your own expected voltages for bright light, room light, and darkness. Show each calculation. Add the results to your table.
Measure and Compare
Keep the batteries connected and set the multimeter to DC voltage (V⎓).
Put the black probe on battery − (0 V).
Put the red probe on the connection between the fixed resistor and the LDR.
Measure the voltage in bright light, room light and darkness. Record each result in the table.
Compare your measured voltages with your calculations.
Does the pattern make sense?
The voltage should be lowest in bright light and highest in darkness.
If your results differ from your predictions, think about whether the light falling on the LDR was the same when you measured its resistance and its voltage.
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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