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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:
🦺 Wear safety glasses
Wear safety glasses when soldering, trimming component legs, or working near someone doing these tasks. Wear safety goggles over prescription glasses.
🚨 Fire safety
Keep the hot iron away from cardboard. If the cardboard starts smoking or scorching, put the iron in its holder and tell your teacher immediately.
💧 Burns – what to do
Know where the nearest running water is.
If you burn yourself, start cooling it immediately under cool running water for 20 minutes—don’t wait for permission.
Tell your teacher straight away, or ask someone to tell them while you cool the burn.
Your teacher will arrange further help if needed.
🔥 Soldering irons
A hot soldering iron belongs in your hand while soldering or in its holder. Never leave it on the bench.
💸 Use solder carefully
Use only enough solder to make a secure joint. Don’t make unnecessary puddles or use the iron to melt other materials.
Step 1: Adding the Copper Tape
Step 1: Adding the Copper Tape
1. Follow the marked lines
Stick the copper tape along the light green lines on your template. Keep it flat and follow the layout carefully.
Where pieces join, overlap their ends. If a piece is too short, overlap another piece to complete the track. Keep separate tracks apart—tape touching across a gap can cause a short circuit.
2. Press the tape down
Use the back of your fingernail or a smooth tool to press the tape firmly onto the template. Smooth out any raised edges.
3. Solder every overlap
The adhesive between overlapping pieces can prevent a reliable electrical connection. Solder every overlap, even if the pieces appear to be touching.
Place the side of the soldering iron tip against the copper at the overlap.
Hold it steady for about 2–3 seconds to heat the copper.
Feed a small amount of solder onto the heated joint, close to the tip.
Let the solder spread across the overlap, then remove the solder wire before the iron.
Aim for a smooth joint that joins both pieces of tape. Do not poke the iron up and down or leave a large blob of solder. Heating for too long can damage the template or lift the tape.
4. Check your work
Check that the tape is firmly attached, every overlap is soldered, and no solder bridges the gaps between separate tracks.
Keep the template flat. Fold it only when instructed later—folding too early can damage the copper tracks.
Teacher checkpoint
Show your teacher your copper tape layout and soldered joints.
Get teacher approval before collecting your resistor.
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.
Measuring resistance accurately
Hold the probes against the component legs. Avoid touching both metal legs or probe tips with your fingers while measuring—your body can provide another path for current and change the reading.
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.
Step 3: Adding the LDR
Step 3: Adding the LDR
An LDR responds to light: When more light reaches its sensing face, its resistance decreases. When the light is blocked, its resistance increases.
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.
Draw your results table
In the blank square on your template, use a pencil and ruler to copy the table shown below.
Teacher checkpoint: Show your teacher your completed table layout before collecting your LDR.
Measure the LDR’s resistance in bright light, room light and darkness. 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.
Before soldering the LDR:
Show your teacher your measured fixed-resistor value and your LDR readings for bright light, room light and darkness.
Get teacher approval before soldering the LDR in place.
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: Predict and Test Voltage Divider
Step 4: Predict 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 as a result of Ohm's Law.
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.
What happens to the output voltage when more light falls on the LDR?
Explain what happens to the LDR's resistance.
⚡ Important: This output voltage is not fixed. It changes depending on the light level, because the LDR’s resistance changes with light.
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.
You have to measure the actual voltage of your battery first. See below.
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.
Turn the battery pack OFF.
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.
Now calculate your own expected voltages for bright light, room light, and darkness. Show each calculation. Add the results to your table.
Worked example: The battery measures 6.2 V. The fixed resistor measures 98 kΩ, and the LDR measures 2 kΩ in bright light.
After the voltage-divider calculations:
Show your teacher your battery voltage and all three calculations.
Get teacher approval before measuring the voltage across the LDR
Measure and Compare
Turn on the battery pack
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 across the LDR in each light condition:
Room light: Lift the template so the LDR underneath is exposed to the room light.
Bright light: Keep the template lifted and shine a torch directly onto the LDR from underneath.
Darkness: Cover the LDR completely so no light reaches it.
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.
TEACHER CHECKPOINT
Show your teacher your calculated and measured LDR voltages for bright light, room light and darkness.
Get teacher approval before collecting and adding your LED.
Step 5: Add LED
Step 5: Add LED
What’s an LED?
The LED provides the light for your nightlight. Fit and check it before adding the transistor.
✅ Step-by-Step Instructions
✅ Step-by-Step Instructions
1️⃣ Choose Your LED Colour
Choose red, orange, yellow, or blue.
For this project, avoid the green LEDs supplied—they have sometimes failed in this circuit.
2️⃣ Identify the LED Legs
An LED must be connected the correct way around.
Long leg = positive (+), called the anode.
Short leg = negative (−), called the cathode.
The flat edge on the LED body also marks the negative side.
3️⃣ Fit and Solder the LED
Turn the battery switch OFF.
Double-check the LED’s direction against the template.
Use pliers to bend the legs carefully onto the correct copper tape tracks.
Trim the legs so they don’t touch other tracks or each other.
Pre-tin the copper tape and LED legs.
Solder the LED legs securely to the copper tape.
⚠️ A leg touching the wrong track, such as the base track, can cause a short circuit and damage the LED or transistor.
🛑 Teacher Check
Ask your teacher to check that your LED is correctly soldered before adding the transistor.
Once approved, move on to fitting the transistor.
Step 6: Adding Transistor
Step 6: Adding Transistor
What’s happening so far?
Your voltage divider produces a changing voltage:
Bright light: the LDR’s resistance is low, so the voltage across it is low.
Room light: the voltage is somewhere between your bright and dark readings.
Darkness: the LDR’s resistance is high, so the voltage across it is higher.
Check your results: does the voltage increase as the LDR gets darker? This is a sanity check—checking whether the results make sense.
Why do we need another component?
The voltage divider gives us a signal that changes with the light level. However, its high resistance limits the current it can supply, so it cannot directly power the LED properly.
We need an electronic switch that uses this signal to control the LED.
Enter the transistor
A transistor can work as an electronic switch.
In your circuit, the voltage divider connects to the transistor’s base. When it gets dark, the signal allows a small base current to flow. This switches the transistor on, allowing a larger current to flow through the LED.
Transistors Explained
The LDR senses the light level. The transistor switches the LED on.
Watch the first 5 minutes of the video.
Focus on how a transistor works as an electronic switch, using a small signal to control the current through a light. You do not need to watch the rest for this project.
✅ Step-by-Step Instructions
✅ Step-by-Step Instructions
1️⃣ Remember What the Transistor Does
In this project, the transistor acts as an electronic switch.
A small current into its base, controls a larger current through the LED.
Make sure you have watched the first 5 minutes of the video above.
2️⃣ Identify the Pins
Our BC547 transistor has three pins:
Collector (C) – connects to the LED.
Base (B) – connects to the voltage divider.
Emitter (E) – connects to battery negative (ground).
Use the pin diagram to identify each leg.
BC 547 - Pin Diagram
3️⃣ Fit the Transistor
Turn the battery switch OFF.
Match the transistor’s direction and C, B and E legs to the template.
Carefully bend the legs so the body lies flat against the card as shown in the image.
Make sure the legs don’t touch each other or the wrong tracks.
4️⃣ Solder the Transistor
Pre-tin the copper tape and transistor legs.
Solder each leg to its correct track.
Use a small amount of solder and heat only as long as needed.
Step 7: Test the Circuit
Step 7: Test the Circuit
Turn the battery switch ON.
Shine a torch on the LDR—the LED should turn off.
Cover the LDR—the LED should turn on.
Not working? Turn the switch OFF and check:
Component legs: Are long legs touching other tracks? Trim them.
Solder joints: Are the copper tape overlaps properly joined with solder?
Transistor: Is it the correct way around, with C, B and E on the correct tracks?
Batteries: Are both fitted the correct way around?
LED: Is it the correct way around? It may need replacing if damaged.
Broken tracks: Look closely at fold lines, especially beside the door. Repair a break with solder, or add a copper tape bridge and solder both ends.
Fix any mistakes, then turn the switch ON and test again.
🛑 Checkpoint: Final Circuit and Soldering Assessment
Keep your template flat. Ask your teacher to assess your working circuit and soldering for your final grades.
Only fold the template after your teacher has approved it.
Step 8: Complete your House: Glue-Up
Step 8: Complete your House: Glue-Up
1️⃣ Get Ready
Complete your final circuit and soldering assessment before folding.
Colour the walls and roof before folding—it’s easier while the template is flat.
Choose a glue station.
Turn the battery switch OFF before folding and gluing.
2️⃣ Glue One Wall and Half the Roof
Carefully fold the template.
Use a tiny dot of glue on each tab.
Glue just one wall and half the roof first.
Press gently and let the glue set. Keep fingers away from hot glue.
3️⃣ Test Again
Turn the switch ON and test the nightlight in light and darkness.
Folding can crack the copper tracks.
If it stops working, turn the switch OFF and check the tracks while the house is still open. Ask for help if needed.
4️⃣ Finish Gluing
If the circuit works, turn the switch OFF and glue the remaining walls and roof.
Keep using tiny dots of glue.
Test once more when finished.
Step 9: Decoration and Marking – Bringing Your Night Light House to Life
Step 9: Decoration and Marking – Bringing Your Night Light House to Life
Add Your Finishing Touches
Use colouring pencils, pens, extra card or paper.
Add details such as curtains, roof tiles, flower pots, a chimney or a fence.
Keep the LDR uncovered and the battery switch accessible.
Be neat and take care with your finished circuit.
Optional: Give your house a name and write a short backstory on a separate card.
Self-Marking
Look at your finished house:
Have you added thoughtful details?
Is your decorating neat and carefully finished?
Give yourself a mark out of 10 for effort and creativity. Explain your mark in one sentence.
Final Marking
Your teacher will assess your decoration based on:
Function: Does it turn on in darkness and off in bright light?
Attention to detail
Care in the finished work
Creativity and effort
Aim for Excellence: Make sure your nightlight works, add creative details, and finish your house with care.
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