Advanced Power Outlet

This project demonstrates how to build an Advanced Power Outlet using basic electronic components only, without using any microcontrollers or programmable devices. The main goal of this project is to understand and apply the fundamentals of electronics through a practical, real-world application.

Unlike a standard power outlet that simply delivers power, this advanced power outlet provides essential protection and monitoring features. It includes under-voltage protection, over-voltage protection, and over-current protection, all implemented using analog circuitry. Each protection threshold can be adjusted using setpoints, allowing the user to clearly observe how voltage and current limits affect the system.

In addition to protection, the outlet also displays the real-time current value using a seven-segment display, helping users visually understand load behavior without relying on software or digital processing.

This project is ideal for students, beginners, and electronics enthusiasts who want to move beyond simulations and theory and gain hands-on experience with comparators, sensing circuits, relays, and display driving techniques. By building this project, you can develop a strong foundation in electronics while creating a useful and educational device.

Step-down Transformer (230 V AC to 12 V AC, 500 mA) – 1

Relay (12 V DC coil, 10 A contacts) – 1

Current Sensor (ACS712) – 1

Voltage Regulator (LM7812) – 1

Voltage Regulator (LM7805) – 1

Operational Amplifier (LM324) – 1

Quad Comparator (LM339) – 1

Comparator / Transistor Array (LM3904) – 2

Priority Encoder (LM74147) – 2

BCD to Seven-Segment Driver (CD4511) – 3

Hex Inverter IC (7404) – 4

Quad NOR Gate IC (7402) – 1

Seven-Segment Display (compatible with CD4511) – 3

Rectifier Diode (1N4007) – 4

Flyback Diode (1N4007) – 1

Signal Diode (1N4148 or equivalent) – As required

NPN Transistor (BC547 / 2N3904) – 2

Indicator LED (Red / Green) – As required

Capacitors and resistors – As required

Single-layer PCB (Analog, ADC, Display boards) – 3

Jumper Wire (Copper wire for PCB jumpers) – As required

Connectors (Screw terminals / headers) – As required

Enclosure (Insulated) – 1

This is the functional diagram of the device

1. Power Supply Unit (P/S) and Voltage sense

Components: Transformer (230V to 12V full wave 500mA), Rectifier Diodes, LM7812, LM7805.

The power supply unit converts the AC mains input into stable DC voltages required by the circuit.

The transformer steps down the mains voltage.

Diodes form a rectifier to convert AC to DC.

The LM7812 provides regulated 12 V for relays and analog circuits.

The LM7805 supplies regulated 5 V for logic ICs and display circuits.

2. Voltage Sensing Unit

Components: 50k Pot as Voltage Divider (Potentiometer).

The voltage divider place between one secondary phase and common wire. The output (center of resistor) fed in to analog filter in amp circuit.

The potentiometer allows adjustment of sensing levels.

The scaled voltage is suitable for processing by op-amps and comparators.

This unit enables under-voltage and over-voltage detection.

3. Current Sensing Unit

Components: ACS712 Hall-Effect Current Sensor

The ACS712 sensor measures the load current flowing through the outlet using the Hall-effect principle.

Provides electrical isolation between power and control circuits.

Outputs a proportional analog voltage representing load current.

This signal is used for over-current protection and current display.

4. Voltage and Current Signal Filtering & Rectification

Components: RC Low-Pass Filter, Diodes

Raw sensing signals may contain noise and ripple.

RC low-pass filters smooth high-frequency noise.

Diodes help rectify and stabilize the sensed signals.

This ensures a steady and accurate voltage level for further processing.

5. Voltage Follower (Buffer Stage)

Components: LM324

The voltage follower provides high input impedance and prevents loading of the sensing circuits.

Buffers voltage and current signals before comparison.

Improves accuracy and stability of measurements.

6. Comparator Unit

Components: LM339 Quad Comparator

The LM339 compares sensed voltage and current levels with preset reference values.

Separate comparator channels handle:

Under-voltage detection

Over-voltage detection

Over-current detection

If any parameter exceeds the safe limit, a fault signal is generated.

7. On Delay Timer

Components: RC Network, Transistor BC547, 7404 Inverter

At power-on a load, transient surges and voltage spikes may occur.

The RC timer introduces a short delay before enabling the output.

Prevents false triggering due to inrush current and noise.

This improves system reliability and safety.

8. SR Latch (Fault Memory)

Components: 7402 NOR Gate IC

Once a fault condition occurs, the SR latch stores the fault state.

Prevents automatic re-enabling after a fault.

Requires manual reset for safety.

This ensures the outlet remains OFF during abnormal conditions.

9. Relay Control Unit

Components: 12 V DC, 10 A Relay

The relay physically connects or disconnects the mains power to the output socket.

Controlled by the protection logic.

Provides electrical isolation between control and power circuits.

10. Analog-to-Digital Conversion and Display System

Components:

LM3914 ×2 (Comparator Array)

LM74147 ×2 (Priority Encoder / Multiplexer)

7404 ×2 (Logic Inverters)

CD4511 ×3 (Seven-Segment Display Drivers)

Diode Array (1N4148 Diodes)

This block converts analog current values into a digital format suitable for display.

Comparator arrays convert analog levels into digital steps.

Encoders and logic ICs generate BCD signals.

CD4511 drivers directly control the seven-segment displays.

Diode arrays isolate shared input lines between display drivers.

The PCBs were designed as single-layer boards to make troubleshooting and modification easier, especially since several issues were encountered during the initial design stage. Due to these constraints, copper wires were used as jumpers to complete required connections on the single-layer PCB. The system is implemented using three separate PCBs: one for the analog circuitry, one for the ADC and logic section, and one for the indicator and seven-segment display unit.

Calibration

The ADC section must be calibrated before normal operation. In the ADC circuit, two variable resistors are connected to the LM3914 ICs to adjust the low-level (LL) and high-level (HL) reference voltages. These adjustments ensure that the seven-segment display shows the correct current value.

After calibrating the display, the current limiter function should be checked and adjusted to ensure it trips at the desired current level.

Finally, the voltage protection thresholds must be set using variable resistors in the voltage comparator circuits. The over-voltage limit should be adjusted to trigger above 250 V, and the under-voltage limit should be set to trigger below 210 V.

The device can be tested under various types of loads. Household heating appliances draw higher currents and are therefore suitable for testing the device.

This Advanced Power Outlet project demonstrates how fundamental analog and digital electronics can be combined to create a practical and protective mains power device—without using microcontrollers. By implementing voltage and current sensing, adjustable protection thresholds, relay control, and a seven-segment display, this build offers hands-on experience with regulation, comparators, timing circuits, and digital logic. With further calibration and testing under different load conditions, this outlet can serve as a useful learning tool and a reliable power interface for workshops or labs.