Low-cost Night Lamp
This straightforward and inexpensive night light turns on by itself as it gets dark and turns off when the sun comes up. It has a battery charging circuit that offers safety against overc…
Know the mission before touching a wire.
Understand what you are making, prepare the right tools, and make the workbench safe.
Project details
Low-cost Night Lamp is a electronics project. This straightforward and inexpensive night light turns on by itself as it gets dark and turns off when the sun comes up. It has a battery charging circuit that offers safety against overc…
- Source pages
- 200-202
- Named parts
- 6
- Build goal
- Working, tested prototype
Tools you need
- Digital multimeter
- Wire stripper and side cutters
- Soldering iron with a fine tip
- Current-limited bench supply
Use eye protection, good lighting, and a clean insulated surface throughout the build.
Safety precautions
- Disconnect every power source before changing a connection.
- Check component polarity, pinout, and supply voltage twice.
- Use a current limit for the first power-up.
- This project may involve hazardous voltage. Work only with qualified supervision and proper isolation.
Gather, identify, and understand every part.
Use the standardized inventory, then open What's this? to learn each part's role, advantages, limitations, handling, and specifications.
What's this?Image, role, pros, cons, handling & specifications
Power supply
A power component supplies, converts, stores, or regulates energy for the project.
What it does hereIt must provide the documented voltage, polarity, isolation, and sufficient current safely.
Buy / compare this part ↗Advantages
- Stable power improves reliability
- Current limiting protects first tests
- Regulation reduces resets and noise
Limitations
- Wrong polarity can cause immediate damage
- Underrated parts overheat
- Mains circuits require qualified supervision
Handling
- Measure output before connection
- Use a fuse or current limit
- Insulate exposed conductors
Specifications to verify
- Use the exact model, value, package, and rating listed for Power supply; similar-looking parts are not always interchangeable.
- Confirm input/output voltage, current, polarity, connector, isolation, and thermal rating.
What's this?Image, role, pros, cons, handling & specifications
Transformer
A power component supplies, converts, stores, or regulates energy for the project.
What it does hereIt must provide the documented voltage, polarity, isolation, and sufficient current safely.
Buy / compare this part ↗Advantages
- Stable power improves reliability
- Current limiting protects first tests
- Regulation reduces resets and noise
Limitations
- Wrong polarity can cause immediate damage
- Underrated parts overheat
- Mains circuits require qualified supervision
Handling
- Measure output before connection
- Use a fuse or current limit
- Insulate exposed conductors
Specifications to verify
- Use the exact model, value, package, and rating listed for Transformer; similar-looking parts are not always interchangeable.
- Confirm input/output voltage, current, polarity, connector, isolation, and thermal rating.
What's this?Image, role, pros, cons, handling & specifications
Operational amplifier
A named project component whose exact role is defined by the source circuit and build guide.
What it does hereIt performs a documented electrical, control, interface, or construction function in this project.
Buy / compare this part ↗Advantages
- Selected for this project
- Can be checked independently
- Supports modular troubleshooting
Limitations
- Substitutes may differ
- Generic names can hide variants
- Pinouts and ratings vary
Handling
- Compare the received part with the source
- Keep it labelled
- Do not force connectors or adjusters
Specifications to verify
- Use the exact model, value, package, and rating listed for Operational amplifier; similar-looking parts are not always interchangeable.
- Confirm dimensions, ratings, connection method, polarity, and environmental limits.
What's this?Image, role, pros, cons, handling & specifications
7812 - integrated circuit
A power component supplies, converts, stores, or regulates energy for the project.
What it does hereIt must provide the documented voltage, polarity, isolation, and sufficient current safely.
Buy / compare this part ↗Advantages
- Stable power improves reliability
- Current limiting protects first tests
- Regulation reduces resets and noise
Limitations
- Wrong polarity can cause immediate damage
- Underrated parts overheat
- Mains circuits require qualified supervision
Handling
- Measure output before connection
- Use a fuse or current limit
- Insulate exposed conductors
Specifications to verify
- Use the exact model, value, package, and rating listed for 7812 - integrated circuit; similar-looking parts are not always interchangeable.
- Confirm input/output voltage, current, polarity, connector, isolation, and thermal rating.
What's this?Image, role, pros, cons, handling & specifications
T1, T2, T3, T4 - transistor stages identified in the circuit
A semiconductor stage performs switching, amplification, regulation, rectification, or logic.
What it does hereIt controls current or signal flow at a defined point in the circuit.
Buy / compare this part ↗Advantages
- Fast and efficient
- Compact
- Can control larger loads from smaller signals
Limitations
- Pin order varies
- Sensitive to overvoltage and reverse polarity
- May need cooling or bias components
Handling
- Verify the datasheet pinout
- Avoid static and soldering heat
- Check notch, stripe, or flat-face orientation
Specifications to verify
- Use the exact model, value, package, and rating listed for T1, T2, T3, T4 - transistor stages identified in the circuit; similar-looking parts are not always interchangeable.
- Confirm pinout, maximum voltage/current, dissipation, gain or forward voltage, and package.
What's this?Image, role, pros, cons, handling & specifications
LED1, LED2, LED9 - indicator LEDs identified in the circuit
A named project component whose exact role is defined by the source circuit and build guide.
What it does hereIt performs a documented electrical, control, interface, or construction function in this project.
Buy / compare this part ↗Advantages
- Selected for this project
- Can be checked independently
- Supports modular troubleshooting
Limitations
- Substitutes may differ
- Generic names can hide variants
- Pinouts and ratings vary
Handling
- Compare the received part with the source
- Keep it labelled
- Do not force connectors or adjusters
Specifications to verify
- Use the exact model, value, package, and rating listed for LED1, LED2, LED9 - indicator LEDs identified in the circuit; similar-looking parts are not always interchangeable.
- Confirm dimensions, ratings, connection method, polarity, and environmental limits.
Connect one verified path at a time.
Explore the named components and standardized signal flow, then use Source Check to verify exact physical pins, values, and topology before applying power.
Trace this circuit.
Low-cost Night Lamp: interactive parts, standardized terminals, responsive anchored wires, student explanations, and the original circuit reference in one shared system.
Trace before wiring
Follow power, ground, inputs, processing, and outputs in that order. Never guess a pin from package shape alone.
Connect with power off
Make short, labelled connections and share a common ground only where the schematic requires it.
Inspect every joint
Check continuity, polarity, adjacent shorts, and loose connections before the first power-up.
Open all source diagrams and build views 1 visuals
Confirm the hardware-only control path.
This project does not include firmware in the source. The circuit itself provides the required behaviour.
How to connect
- Match every controller label to the circuit view and source pin map.
- Join grounds before signal wires when separate low-voltage supplies are used.
- Keep motors, relays, pumps, and other loads on a suitable driver and external supply.
Common mistakes
Reversed VCC/GND, board-label versus GPIO-number confusion, missing common ground, and charge-only USB cables.
Troubleshoot
Disconnect loads, continuity-test one path at a time, then test with a current limit.
Software preparation
No IDE, board package, library, or firmware upload is required for this project.
If you add a programmable controller as an extension, document its pin map separately.
How to upload code
The original design is implemented entirely in hardware, so proceed after verifying the circuit and supply.
Assemble, deploy, test, and troubleshoot.
Use the complete source notes in build order, then pass the final checks before calling the project finished.
Build in functional stages
- Power and regulation
- Controller or processing stage
- Inputs and sensors
- Outputs and loads
- Enclosure and strain relief
Power up safely
- Inspect unpowered continuity first
- Apply the lowest safe current limit
- Measure supply rails before signals
- Add one load at a time
- Record expected and actual results
Work from simple to complex
- Confirm power, ground, polarity, and orientation
- Compare each pin with the source
- Test inputs separately from outputs
- Replace only one variable at a time
- Power off before every correction
Follow the documented instructions.
These notes come from this project's source and remain in their original order.
Project overview
Project build noteThis straightforward and inexpensive night light turns on by itself as it gets dark and turns off when the sun comes up. It has a battery charging circuit that offers safety against overcharging as well as deep discharging the battery. The circuit can be broken down into three distinct parts: the power supply, the control for overcharging and undercharging, and the lamp control. A low-cost night lamp circuit The power supply section consists of the bridge rectifier BR1, regulator IC3, and regulator IC4 as well as the transformer X1. The mains voltage of 230 volts AC is reduced to 12 volts AC by transformer X1, which is then rectified by bridge rectifier BR1 and filtered by capacitor C4. Regulators 7809 and 7812 are responsible for bringing the output of the rectifier down to 9V and 12V, respectively. While 9V is utilized to charge the battery and power the lamp control circuit, 12V comes from the supply and is used for the operation of the relay RL1. The overcharging/undercharging
control section is constructed using IC2 and a few discrete components as its primary building blocks. Circuit operation Even when there is power from the mains supply and the battery voltage is between 5.5V and 6.5V, the relay will not become energized. Under these circumstances, the battery is charged by relay RL1's normally-closed contacts, which are denoted with a N/C designation. When the voltage of the battery drops below 5.5 volts, the voltage at the inverting pin 9 of the circuit drops below 3.6 volts. As a consequence of this, the output of the operational amplifier N2 climbs high, and the transistor T4 conducts, which activates the relay RL1 to stop the battery from going into a deep discharge. In a similar manner, if the voltage of the battery rises above 6.5V, then the voltage at the non-inverting pin 12 of the battery rises above 3.6V. As a consequence of this, the output of the operational amplifier N1 swings high, and the transistor T4 conducts, which activates the relay RL1 to stop the battery from being overcharged. When one of these conditions is present—overcharging or deep discharging—LED1 illuminates to alert the user.
Construction & testing
Project build noteIn order to create the control circuit for the light, components IC1, transistors T1 through T3, some resistors, and capacitors were used, and the lamp itself is composed of white LEDs (LED2 through LED9). During the day, the resistance of LDR1 is decreased since light is falling on it. As a consequence of this, transistor T1 conducts, which pulls reset pin 4 of integrated circuit IC1 low to disable it and thus turns off all of the white LEDs. When it is nighttime, also known as when it is dark, the resistance of LDR1 rises, which results in the transistor T1 being turned off. In order to turn on IC1, the reset pin 4 is pulled high, and at the same time, trigger pin 2 is pulled low by means of transistor T2. Through the transistor T3, the high output located at pin 3 of the IC illuminates all of the white LEDs.
You built Low-cost Night Lamp.
You followed the full workflow from understanding the mission to testing the finished project. That is a real engineering achievement - well done.
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