Standby Power-Loss Preventer
Electronics still use some power even when they are in the standby mode, which is when they have been turned off with a remote but not the mains power switch. For example, a CRT TV or PC…
Know the mission before touching a wire.
Understand what you are making, prepare the right tools, and make the workbench safe.
Project details
Standby Power-Loss Preventer is a electronics project. Electronics still use some power even when they are in the standby mode, which is when they have been turned off with a remote but not the mains power switch. For example, a CRT TV or PC…
- Source pages
- 424-426
- Named parts
- 5
- 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
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
T1 - transistor stage 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 - transistor stage 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 - 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.
What's this?Image, role, pros, cons, handling & specifications
PART LEARNING VIEWVR1 - preset potentiometer 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 VR1 - preset potentiometer 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.
Standby Power-Loss Preventer: 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 noteElectronics still use some power even when they are in the standby mode, which is when they have been turned off with a remote but not the mains power switch. For example, a CRT TV or PC monitor uses 80 to 100 watts of power when it is on. Even when it's not doing anything, it uses a few watts of power. So, if you leave these devices on standby for a long time, they may cause your electricity bill to go up. The circuit described here can help you save money on your electricity bill by automatically cutting off the power to a device (like a CRT TV) when you turn it off with the remote. (But you might need to get up and turn the TV back on!) The circuit is turned on by the idea of electromagnetic induction.
When the CRT monitor is "on," the circuit can pick up the high-energy electromagnetic radiation coming from it. A relay coil (L1) connected between the inverting pin 2 and the non-inverting pin 3 of IC CA3130 (IC1) picks up the monitor's electromagnetic radiation to make a small current. IC CA3130 is a CMOS operational amplifier with p-channel MOSFETs that have their gates protected. It needs a very low input current and has a very high input impedance (typically, 5 pA). IC1 is a good choice for this application because it has a high input impedance and a low input current. The 5 pA internal bias of IC1 is enough for it to work, so it doesn't need an external bias. Offset null adjustments are made with VR1, so that when the TV is in standby mode, the output of IC1 is low. When the TV is first "off," pin 6 of IC1 is low, so LED1 doesn't light up. Press the S1 switch for a few seconds to turn on the TV. Through resistor R2, capacitor C1 gets charged up, and when transistor T1 conducts, it turns on relay RL1. The relay's normally-open (N/O) contacts send power to the TV. When the TV is turned on, electromagnetic radiation hits the sensor coil. This makes the output of IC1 go high, which makes LED1 light up. Diode D1 connects the high output of IC1 to the non-inverting input of IC TLO71 (IC2), so the TV stays "on." IC2 is a low-noise op-amp with a JFET input. When you use the remote to turn off the TV, the electromagnetic field around it goes away, and IC1's output goes down. So, the output of IC2 also goes low, and transistor T1 stops conducting. The time it takes for capacitor C1 to discharge through resistor R3 gives a delay of a few seconds to de- energize the relay, after which the mains power to the TV is cut off. The only way to turn the TV back on is to briefly press switch S1.
The circuit gets its power from a step-down transformer that goes from 12V to 0V to 12V. (X1). The secondary output of the transformer is fixed by diodes D3 and D4, and ripples are smoothed out by capacitor C3. The IC 7809 (IC3) gives the circuit the 9V it needs to work. Put the circuit together on a general-purpose PCB and put it in a box with an AC plug for the TV. Place the unit close to the TV, preferably on top or on the side, and plug it in. Set VR1 so that LED1 goes out. At this point, the relay shouldn't be turned on. Press switch S1 for a few seconds, until the relay turns on and LED1 lights up. This turns on the TV. If you now let go of switch S1, the TV will stay "on." In standby mode, use the remote to turn it off.
You built Standby Power-Loss Preventer.
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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