Power-on Reminder with LED Lamp
The majority of the time, the equipment at workstations is left on without anyone noticing it. In this situation, these might get too hot and break. Here is an add-on for the workbench po…
Know the mission before touching a wire.
Understand what you are making, prepare the right tools, and make the workbench safe.
Project details
Power-on Reminder with LED Lamp is a electronics project. The majority of the time, the equipment at workstations is left on without anyone noticing it. In this situation, these might get too hot and break. Here is an add-on for the workbench po…
- Source pages
- 55-56
- Named parts
- 26
- 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
PWR1 - regulated +12V DC workbench-supply input with 0V return
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 PWR1 - regulated +12V DC workbench-supply input with 0V return; 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
SEMICONDUCTOR LEARNING VIEWIC1 - NE555 astable timer (DIP-8)
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 IC1 - NE555 astable timer (DIP-8); 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
SEMICONDUCTOR LEARNING VIEWIC2 - CD4017 decade counter (DIP-16)
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 IC2 - CD4017 decade counter (DIP-16); 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
PART LEARNING VIEWPZ1 - polarized 9V active buzzer
An output component turns an electrical control signal into light, sound, motion, switching, or displayed information.
What it does hereIt presents the circuit result or acts on the physical world.
Buy / compare this part ↗Advantages
- Makes system state visible
- Can be tested separately
- Supports clear troubleshooting
Limitations
- Loads may exceed controller current
- Polarity or driver direction can matter
- Inductive loads create voltage spikes
Handling
- Use the documented driver stage
- Check polarity and load current
- Add flyback protection for inductive loads
Specifications to verify
- Use the exact model, value, package, and rating listed for PZ1 - polarized 9V active buzzer; similar-looking parts are not always interchangeable.
- Confirm voltage, current, polarity, interface, driver requirements, and duty cycle.
What's this?Image, role, pros, cons, handling & specifications
POWER LEARNING VIEWBAT1 - 9V rechargeable PP3 backup battery
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 BAT1 - 9V rechargeable PP3 backup battery; 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
POWER LEARNING VIEWS1 - SPST on/off switch for the backup-battery branch
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 S1 - SPST on/off switch for the backup-battery branch; 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
PASSIVE LEARNING VIEWLDR1 - two-terminal light-dependent resistor
A passive component sets current, voltage, timing, filtering, or signal behaviour without adding gain.
What it does hereIts exact value and tolerance determine how the surrounding stage behaves.
Buy / compare this part ↗Advantages
- Simple and dependable
- Low cost
- Easy to measure before installation
Limitations
- A wrong value can stop or damage the circuit
- Ratings must not be exceeded
- Polarized parts require correct orientation
Handling
- Measure unclear values
- Observe capacitor polarity
- Avoid overheating leads while soldering
Specifications to verify
- Use the exact model, value, package, and rating listed for LDR1 - two-terminal light-dependent resistor; similar-looking parts are not always interchangeable.
- Confirm value, tolerance, power or voltage rating, polarity, and package size.
What's this?Image, role, pros, cons, handling & specifications
SEMICONDUCTOR LEARNING VIEWT1 - BC548 NPN ambient-light threshold transistor
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 - BC548 NPN ambient-light threshold transistor; 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
PART LEARNING VIEWT2 - BC548 NPN white-LED driver transistor
An output component turns an electrical control signal into light, sound, motion, switching, or displayed information.
What it does hereIt presents the circuit result or acts on the physical world.
Buy / compare this part ↗Advantages
- Makes system state visible
- Can be tested separately
- Supports clear troubleshooting
Limitations
- Loads may exceed controller current
- Polarity or driver direction can matter
- Inductive loads create voltage spikes
Handling
- Use the documented driver stage
- Check polarity and load current
- Add flyback protection for inductive loads
Specifications to verify
- Use the exact model, value, package, and rating listed for T2 - BC548 NPN white-LED driver transistor; similar-looking parts are not always interchangeable.
- Confirm voltage, current, polarity, interface, driver requirements, and duty cycle.
What's this?Image, role, pros, cons, handling & specifications
POWER LEARNING VIEWD5 - 1N4001 battery-discharge steering diode
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 D5 - 1N4001 battery-discharge steering diode; 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
PASSIVE LEARNING VIEWD6 - 1N4001 +12V-to-backup-rail isolation diode
A passive component sets current, voltage, timing, filtering, or signal behaviour without adding gain.
What it does hereIts exact value and tolerance determine how the surrounding stage behaves.
Buy / compare this part ↗Advantages
- Simple and dependable
- Low cost
- Easy to measure before installation
Limitations
- A wrong value can stop or damage the circuit
- Ratings must not be exceeded
- Polarized parts require correct orientation
Handling
- Measure unclear values
- Observe capacitor polarity
- Avoid overheating leads while soldering
Specifications to verify
- Use the exact model, value, package, and rating listed for D6 - 1N4001 +12V-to-backup-rail isolation diode; similar-looking parts are not always interchangeable.
- Confirm value, tolerance, power or voltage rating, polarity, and package size.
What's this?Image, role, pros, cons, handling & specifications
PART LEARNING VIEWLED1 - green 5mm count-zero indicator LED
An output component turns an electrical control signal into light, sound, motion, switching, or displayed information.
What it does hereIt presents the circuit result or acts on the physical world.
Buy / compare this part ↗Advantages
- Makes system state visible
- Can be tested separately
- Supports clear troubleshooting
Limitations
- Loads may exceed controller current
- Polarity or driver direction can matter
- Inductive loads create voltage spikes
Handling
- Use the documented driver stage
- Check polarity and load current
- Add flyback protection for inductive loads
Specifications to verify
- Use the exact model, value, package, and rating listed for LED1 - green 5mm count-zero indicator LED; similar-looking parts are not always interchangeable.
- Confirm voltage, current, polarity, interface, driver requirements, and duty cycle.
What's this?Image, role, pros, cons, handling & specifications
PART LEARNING VIEWLED2 - white 5mm emergency-lamp LED
An output component turns an electrical control signal into light, sound, motion, switching, or displayed information.
What it does hereIt presents the circuit result or acts on the physical world.
Buy / compare this part ↗Advantages
- Makes system state visible
- Can be tested separately
- Supports clear troubleshooting
Limitations
- Loads may exceed controller current
- Polarity or driver direction can matter
- Inductive loads create voltage spikes
Handling
- Use the documented driver stage
- Check polarity and load current
- Add flyback protection for inductive loads
Specifications to verify
- Use the exact model, value, package, and rating listed for LED2 - white 5mm emergency-lamp LED; similar-looking parts are not always interchangeable.
- Confirm voltage, current, polarity, interface, driver requirements, and duty cycle.
What's this?Image, role, pros, cons, handling & specifications
PART LEARNING VIEWVR1 - 1MΩ astable-period preset potentiometer
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 VR1 - 1MΩ astable-period preset potentiometer; 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
PART LEARNING VIEWVR2 - 50kΩ darkness-threshold preset potentiometer
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 VR2 - 50kΩ darkness-threshold preset potentiometer; 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
PASSIVE LEARNING VIEWR1 - 10MΩ astable charging resistor
A passive component sets current, voltage, timing, filtering, or signal behaviour without adding gain.
What it does hereIts exact value and tolerance determine how the surrounding stage behaves.
Buy / compare this part ↗Advantages
- Simple and dependable
- Low cost
- Easy to measure before installation
Limitations
- A wrong value can stop or damage the circuit
- Ratings must not be exceeded
- Polarized parts require correct orientation
Handling
- Measure unclear values
- Observe capacitor polarity
- Avoid overheating leads while soldering
Specifications to verify
- Use the exact model, value, package, and rating listed for R1 - 10MΩ astable charging resistor; similar-looking parts are not always interchangeable.
- Confirm value, tolerance, power or voltage rating, polarity, and package size.
What's this?Image, role, pros, cons, handling & specifications
PASSIVE LEARNING VIEWR2 - 6.8MΩ astable charging resistor
A passive component sets current, voltage, timing, filtering, or signal behaviour without adding gain.
What it does hereIts exact value and tolerance determine how the surrounding stage behaves.
Buy / compare this part ↗Advantages
- Simple and dependable
- Low cost
- Easy to measure before installation
Limitations
- A wrong value can stop or damage the circuit
- Ratings must not be exceeded
- Polarized parts require correct orientation
Handling
- Measure unclear values
- Observe capacitor polarity
- Avoid overheating leads while soldering
Specifications to verify
- Use the exact model, value, package, and rating listed for R2 - 6.8MΩ astable charging resistor; similar-looking parts are not always interchangeable.
- Confirm value, tolerance, power or voltage rating, polarity, and package size.
What's this?Image, role, pros, cons, handling & specifications
SEMICONDUCTOR LEARNING VIEWR3 - 10kΩ CD4017 power-on-reset discharge resistor
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 R3 - 10kΩ CD4017 power-on-reset discharge resistor; 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
PASSIVE LEARNING VIEWR4 - 470Ω LED1 current-limiting resistor
A passive component sets current, voltage, timing, filtering, or signal behaviour without adding gain.
What it does hereIts exact value and tolerance determine how the surrounding stage behaves.
Buy / compare this part ↗Advantages
- Simple and dependable
- Low cost
- Easy to measure before installation
Limitations
- A wrong value can stop or damage the circuit
- Ratings must not be exceeded
- Polarized parts require correct orientation
Handling
- Measure unclear values
- Observe capacitor polarity
- Avoid overheating leads while soldering
Specifications to verify
- Use the exact model, value, package, and rating listed for R4 - 470Ω LED1 current-limiting resistor; similar-looking parts are not always interchangeable.
- Confirm value, tolerance, power or voltage rating, polarity, and package size.
What's this?Image, role, pros, cons, handling & specifications
POWER LEARNING VIEWR5 - 1kΩ rechargeable-battery charging resistor
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 R5 - 1kΩ rechargeable-battery charging resistor; 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
PASSIVE LEARNING VIEWR6 - 12kΩ T2 base pull-up resistor
A passive component sets current, voltage, timing, filtering, or signal behaviour without adding gain.
What it does hereIts exact value and tolerance determine how the surrounding stage behaves.
Buy / compare this part ↗Advantages
- Simple and dependable
- Low cost
- Easy to measure before installation
Limitations
- A wrong value can stop or damage the circuit
- Ratings must not be exceeded
- Polarized parts require correct orientation
Handling
- Measure unclear values
- Observe capacitor polarity
- Avoid overheating leads while soldering
Specifications to verify
- Use the exact model, value, package, and rating listed for R6 - 12kΩ T2 base pull-up resistor; similar-looking parts are not always interchangeable.
- Confirm value, tolerance, power or voltage rating, polarity, and package size.
What's this?Image, role, pros, cons, handling & specifications
PASSIVE LEARNING VIEWR7 - 100Ω LED2 current-limiting resistor
A passive component sets current, voltage, timing, filtering, or signal behaviour without adding gain.
What it does hereIts exact value and tolerance determine how the surrounding stage behaves.
Buy / compare this part ↗Advantages
- Simple and dependable
- Low cost
- Easy to measure before installation
Limitations
- A wrong value can stop or damage the circuit
- Ratings must not be exceeded
- Polarized parts require correct orientation
Handling
- Measure unclear values
- Observe capacitor polarity
- Avoid overheating leads while soldering
Specifications to verify
- Use the exact model, value, package, and rating listed for R7 - 100Ω LED2 current-limiting resistor; similar-looking parts are not always interchangeable.
- Confirm value, tolerance, power or voltage rating, polarity, and package size.
What's this?Image, role, pros, cons, handling & specifications
C1 - 10µF 25V polarized astable timing capacitor
A passive component sets current, voltage, timing, filtering, or signal behaviour without adding gain.
What it does hereIts exact value and tolerance determine how the surrounding stage behaves.
Buy / compare this part ↗Advantages
- Simple and dependable
- Low cost
- Easy to measure before installation
Limitations
- A wrong value can stop or damage the circuit
- Ratings must not be exceeded
- Polarized parts require correct orientation
Handling
- Measure unclear values
- Observe capacitor polarity
- Avoid overheating leads while soldering
Specifications to verify
- Use the exact model, value, package, and rating listed for C1 - 10µF 25V polarized astable timing capacitor; similar-looking parts are not always interchangeable.
- Confirm value, tolerance, power or voltage rating, polarity, and package size.
What's this?Image, role, pros, cons, handling & specifications
SEMICONDUCTOR LEARNING VIEWC2 - 0.01µF non-polarized NE555 control-pin bypass capacitor
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 C2 - 0.01µF non-polarized NE555 control-pin bypass capacitor; 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
SEMICONDUCTOR LEARNING VIEWC3 - 4.7µF 25V polarized CD4017 power-on-reset capacitor
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 C3 - 4.7µF 25V polarized CD4017 power-on-reset capacitor; 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
C4 - 2200µF 25V polarized buzzer pulse-length capacitor
An output component turns an electrical control signal into light, sound, motion, switching, or displayed information.
What it does hereIt presents the circuit result or acts on the physical world.
Buy / compare this part ↗Advantages
- Makes system state visible
- Can be tested separately
- Supports clear troubleshooting
Limitations
- Loads may exceed controller current
- Polarity or driver direction can matter
- Inductive loads create voltage spikes
Handling
- Use the documented driver stage
- Check polarity and load current
- Add flyback protection for inductive loads
Specifications to verify
- Use the exact model, value, package, and rating listed for C4 - 2200µF 25V polarized buzzer pulse-length capacitor; similar-looking parts are not always interchangeable.
- Confirm voltage, current, polarity, interface, driver requirements, and duty cycle.
Connect one verified path at a time.
Use the pin-reviewed interactive wiring view to inspect real parts, named terminals, and every connection path.
Trace this circuit.
Power-on Reminder with LED 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 2 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 noteThe majority of the time, the equipment at workstations is left on without anyone noticing it. In this situation, these might get too hot and break. Here is an add-on for the workbench power supply that sounds a buzzer for about 20 seconds every hour or so to let you know if the devices you have plugged in are on or off. It also has a white LED that gives off enough light to find things when the power goes out.
In Fig. 1, the circuit of a power-on reminder with an LED light is shown. Here, IC NE555 (IC1) is wired as an astable multivibrator. With resistors R1 and R2, preset VR1, and capacitor C1, the time period is set to about six minutes so that the buzzer goes off every hour. IC1's output is connected to IC CD4017's clock input (IC2). IC2 gets a power-on reset pulse from capacitor C3 and resistor R3. When the power is turned on to the circuit, pin 3 of IC2 goes high. After about an hour, pin 11 (Q9) goes high, and the buzzer goes off. This cycle keeps going until the two npn transistors are reached. In the dark, when no light hits it, the LDR has a very high resistance. So, when the power goes out, the white LED (LED2) lights up because transistor T1 is driven in the wrong direction. The circuit for the lamp is powered by a 9V rechargeable battery, which is charged when mains is present by the resistor R5. So, when it's dark, the LED stays off because the power to the circuit is turned off.
You built Power-on Reminder with LED Lamp.
You followed the full workflow from understanding the mission to testing the finished project. That is a real engineering achievement - well done.
Quality FM Transmitter
Ready to reuse what you learned in another project from the same track?
Start this project →