More project photos (2)
The problem
A lost phase or a reversed phase sequence can quietly destroy a three-phase motor: single-phasing overheats windings, and swapped phases run a pump or conveyor backwards. Factory panels include protection relays for this, but students rarely get to build and understand the detection logic themselves. This project fills that gap — a panel that watches three phases through transformer-isolated, optocoupler-buffered sensing and reports, in real time, whether each phase is present, whether the sequence is R-Y-B or reversed, and whether the phase voltage is inside the healthy band. A 16x2 LCD shows per-phase status, three LEDs give an at-a-glance view, and a buzzer sounds whenever a fault is declared. The design is deliberately built for a college lab: the mains side is stepped down through three small transformers and the controller side stays galvanically isolated, so the demo is safe to demonstrate without direct high-voltage probing. Everything is designed to be explainable in a viva — zero-crossing detection, phase-order logic and threshold comparison are all in the code and documented.
Operator reading the panel and silencing the buzzer.
Follow the working sequence
How it works
- The panel connects to a three-phase supply through three 230V-to-9V step-down transformers (one per phase), keeping the logic side galvanically isolated from the mains side.
- Each transformer secondary drives a PC817 optocoupler channel that emits a pulse at every zero crossing; the Arduino Nano timestamps these pulses with hardware interrupts.
- If pulses stop arriving from a phase for a set number of half-cycles (design target: 4 half-cycles, about 80 ms at 50 Hz), that phase is declared failed.
- The firmware compares the arrival order of the R, Y and B pulses — R-Y-B means correct sequence, R-B-Y means reversed — and reports SEQ OK or SEQ REV on the LCD.
- Each secondary is additionally scaled through a resistor divider into a 10-bit ADC channel; readings outside the buyer-calibrated band raise an under/over-voltage flag for that phase.
- Any declared fault lights the corresponding R/Y/B LED, updates the LCD, and sounds the buzzer; a push-button silences the buzzer, which re-arms on the next new fault.
Tech stack:
- ATmega328P · Arduino Nano (firmware in Arduino C)
- PC817 optocouplers · zero-crossing detection
- 3 × 230V-to-9V AC transformers · galvanic isolation
- 16x2 character LCD (HD44780)
- 5V active piezo buzzer
- R/Y/B panel LEDs · terminal blocks
- White acrylic panel assembly
- Resistor dividers · 10-bit ADC voltage sensing
| Parameter | Value |
|---|---|
| Input sensing | 3 × 230V-to-9V AC transformers, transformer-isolated (design) |
| Controller | ATmega328P @ 16 MHz (Arduino Nano) |
| Sequence detection | Zero-crossing arrival order, R-Y-B vs R-B-Y (design) |
| Fault declaration time | Approximately 80–200 ms (design target, depends on build) |
| Voltage sensing | 3 × 10-bit ADC channels via resistor dividers (design) |
| Display | 16 × 2 character LCD, per-phase status + sequence verdict |
| Alarm | 5V active piezo buzzer, approximately 2.3 kHz (datasheet typical), with mute button |
| Indicators | 3 × panel LEDs (R/Y/B), approximately 20 mA each |
| Logic supply | 5V regulated from one transformer secondary (design) |
| Panel | White acrylic, approximately 240 × 170 mm (design) |
Project features
- [Per-phase presence detection] Each phase is monitored through its own 230V-to-9V transformer plus a PC817 optocoupler zero-crossing channel; if zero-crossing pulses stop arriving for a configurable number of half-cycles, the phase is declared failed and the event is latched on the display.
- [Phase-sequence detection] The firmware timestamps the zero-crossing pulses of R, Y and B and compares their arrival order — R-Y-B is reported as correct sequence, R-B-Y as reversed — which is exactly how the reversal that runs motors backwards is caught.
- [16x2 LCD status readout] The LCD continuously shows R/Y/B per-phase status on line one and the sequence verdict (SEQ OK / SEQ REV) plus any failure flag on line two, so the whole state is readable without a PC.
- [Buzzer fault alarm] A 5V active buzzer sounds on any declared fault — phase loss, reversed sequence or voltage fault — with a push-button to silence it, and it re-arms automatically on the next new fault.
- [R/Y/B indicator LEDs] Three panel LEDs mirror the per-phase status for at-a-glance checking from across the lab, each labelled with a handwritten masking-tape tag in the student-build style.
- [Transformer-isolated, optocoupler-buffered sensing] The three-phase input is stepped down by three separate transformers and each channel is optocoupler-buffered, so the ATmega328P side is galvanically isolated from the mains side by design.
- [Under/over-voltage fault flags] Each transformer secondary is also read through a divider into the 10-bit ADC; firmware compares the measured level against buyer-calibrated thresholds and flags phases that read too low or too high.
What is included
- Assembled indicator panel: controller board, sensing boards, LCD, buzzer, LEDs, transformers, terminal blocks and wiring
- Arduino Nano firmware (zero-crossing detection, sequence logic, threshold comparison, LCD + buzzer drivers)
- Circuit diagram and wiring diagram
- Voltage-threshold calibration procedure for the buyer's lab supply
- Project report PDF (background, sensing design, firmware logic, calibration, results)
- PPT presentation for final review
- Viva Q&A preparation document (zero-crossing detection, optocoupler isolation, phase sequence, fault timing)
Limitations & prerequisites
- The student demo is transformer-isolated and intended for a college lab three-phase supply; it is not a certified mains protection panel and must not be installed permanently on 400V distribution without a certified enclosure and earthing, which is not part of the student build.
- The 80–200 ms fault declaration time is a design target; the actual figure depends on the assembled build and wiring, and is verified with the buyer-run test procedure during delivery.
- Voltage-fault thresholds are approximate: transformer regulation is typically ±10% and the 10-bit ADC resolves about 5 mV per step after the divider, so the delivered calibration procedure sets thresholds against the buyer's own lab supply.
- Sequence detection assumes reasonably balanced phases; heavily unbalanced or harmonic-rich supplies can misread the phase order, which the report documents honestly.
- This is indication only: the build does not trip a contactor or disconnect a motor on fault — a trip output is future scope, not part of the delivered panel.
- The buzzer is an alert, not an alarm system: it can be muted with the push-button and it re-arms only on the next new fault, so unattended faults can go unnoticed once silenced.
- Demonstrating it needs a three-phase supply in the college lab; a single-phase household socket cannot exercise sequence or phase-failure detection.
Frequently Asked Questions
How does it detect wrong phase sequence?
Each phase's zero-crossing pulse is timestamped by the Arduino Nano. The firmware checks the arrival order: R-Y-B is reported as SEQ OK and R-B-Y as SEQ REV. A reversed sequence is what runs a three-phase motor backwards, so catching the order — not just the presence — is the point of the detection.
Does it connect directly to 400V mains?
No. The build is transformer-isolated by design: three 230V-to-9V transformers step the mains down, and each channel passes through a PC817 optocoupler, so the controller side never touches high voltage directly. It is meant to be demonstrated in a college lab on a proper three-phase supply.
What exactly does the LCD show?
Line one shows per-phase status (R:OK Y:OK B:OK, with any failed phase flagged), and line two shows the sequence verdict (SEQ OK or SEQ REV) plus any failure flag. The three R/Y/B panel LEDs mirror the per-phase status for at-a-glance checking.
Does it cut power to a motor when a fault occurs?
No — this build is indication only: LCD, LEDs and buzzer. It does not trip a contactor or disconnect anything. Adding a relay/contactor trip output is listed as future scope in the report, and is deliberately not claimed as implemented.
How fast does it declare a fault?
The design target is 80–200 ms after a phase disappears or a sequence reverses, based on counting missing zero-crossing half-cycles. This is stated as a design target, not a measured figure — the actual build is verified with the buyer-run test procedure during delivery.
Is this project suitable for a final-year project?
Yes — for Electrical, E&TC and IoT programs. It covers transformer isolation, optocoupler interfacing, zero-crossing detection, real-time firmware logic and panel assembly, all demonstrable and explainable in a viva. Suitable for B.E./B.Tech final-year projects in Electrical, E&TC and IoT.
Components & software requirements
- ATmega328P · Arduino Nano (firmware in Arduino C)
- PC817 optocouplers · zero-crossing detection
- 3 × 230V-to-9V AC transformers · galvanic isolation
- 16x2 character LCD (HD44780)
- 5V active piezo buzzer
- R/Y/B panel LEDs · terminal blocks
- White acrylic panel assembly
- Resistor dividers · 10-bit ADC voltage sensing
Delivery information
Built-to-order project. Delivery timeline is shared after order confirmation based on current queue.
Support terms
Complete documentation, setup guide, and viva preparation included. Support for setup and explanation provided.
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