PC Timer
This flexible PC timer with an adjustable time output is designed to be installed in a desktop PC. It controls how long PC peripherals like printers, scanners, and desk lamps stay on. Sin…
Know the mission before touching a wire.
Understand what you are making, prepare the right tools, and make the workbench safe.
Project details
PC Timer is a electronics project. This flexible PC timer with an adjustable time output is designed to be installed in a desktop PC. It controls how long PC peripherals like printers, scanners, and desk lamps stay on. Sin…
- Source pages
- 478-480
- Named parts
- 4
- 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.
- Keep liquids, loose metal, and uninsulated wires away from the bench.
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
CD4060
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 CD4060; 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
CD4093
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 CD4093; 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 - indicator LED identified in the circuit
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 - indicator LED identified in the circuit; similar-looking parts are not always interchangeable.
- Confirm voltage, current, polarity, interface, driver requirements, and duty cycle.
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.
PC Timer: 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 flexible PC timer with an adjustable time output is designed to be installed in a desktop PC. It controls how long PC peripherals like printers, scanners, and desk lamps stay on. Since it is made to work with 12 volts, it might also be useful in your lab. If you plan to use the circuit as a portable timer most of the time, it is best to put it in its own case. If the circuit is going to be used as a PC's internal timer, you could also build it into the PC's case (system box). It is easy to hold the circuit board in place with one of the metal panels that pull out from the back of the PC. What's left to do is drill holes in the metal bracket for the switch (S1), the indicator (LED1), and the connectors for the relay output. PC timer circuit
Connect the circuit's input supply points to the PC's internal power supply cables to connect the input voltage. Any ATX SMPS 4-way drive live power connector that isn't being used (+5V/0V/0V/+12V) can be used to power the circuit. As shown in Fig, the PC's SMPS sends 9V to the circuit through the fixed three-terminal voltage regulator IC 7809 (IC1). Diode D1 protects against accidental polarity reversal. LED1 shows whether the power is on or off. A 14-stage ripple-carry binary counter CD4060 (IC2) and a quad 2-input NAND Schmitt CD4093 are the main parts of the circuit (IC3). After the time set by the R-C time constant components R2 and C5, the timer-controlled relay turns on. With the values of the parts shown (R2 = 470 kilo-ohms and C5 = 100 nF), the relay turns on and latches after 10 minutes. Change the value of R2 and/or C5 to change the time-out period. You can set the time by putting a preset in line with R2 and pin 10 of IC2. To start the timer, just briefly press the S1 switch. IC2 begins to oscillate, and after six seconds, the output of IC3 at pins 3 and 9 gives SCR1 the gate voltage it needs to turn on. So, the relay gets powered up and locks to turn
on the connected load. The relay will stay latched until you press switch S1 again.
You built PC Timer.
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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