Indian LV distribution swings a long way either side of 230 V, and both directions damage appliances: high voltage cooks insulation and filaments, low voltage stalls motor loads so they draw locked-rotor current until something burns. This project samples the mains waveform, computes true RMS voltage rather than trusting a peak reading, and opens a contactor whenever the voltage leaves a settable window. It then holds the load off for a restart delay long enough for a refrigerator compressor to equalise before it is allowed to start again.
Not just the parts. Teams budget from a component list, then run out in week six on wire, connectors and the driver board they destroyed. These are the lines that catch them.
| Line | Cost |
|---|---|
Components and materials From the bill of materials | Rs 3,010 to Rs 7,780 |
Spares and replacements 15 % — you will destroy something | Rs 452 to Rs 1,167 |
Consumables and hardware Wire, connectors, headers, screws, heatshrink | Rs 361 to Rs 934 |
Perfboard and assembly | Rs 150 to Rs 400 |
Report, printing and binding Two or three bound copies, plots and the plagiarism check | Rs 400 to Rs 1,200 |
| Total | Rs 4,373 to Rs 11,481 |
| Each, split 3 ways | Rs 1,458 to Rs 3,827 |
Indicative bands last checked in August 2026 — a guide, not a quotation. Prices move and vary by seller, and anything you can borrow from the lab comes straight off the total. The 2.6 week figure assumes 6 person-weeks of work shared between 3; students past 4 add coordination rather than output, so the estimate stops improving there.
The same chain in words
The ZMPT101B is a small potential transformer, so its output is an isolated, scaled copy of the mains waveform. The op-amp on the module biases it around 2.5 V so the ADC can see both half cycles.
The controller samples that waveform, subtracts the DC offset, squares each sample, averages over a whole number of cycles and takes the square root. That is true RMS, and it stays correct on the distorted waveform a real feeder has, whereas a peak-times-0.707 shortcut does not.
If the RMS value sits outside the window for the full confirmation period, the controller de-energises the contactor and latches the trip with the reason on the display.
After the voltage returns to normal, the restart timer runs before the contactor is allowed to close again, so a compressor is never restarted against a head of pressure.
This is the chapter that separates an engineering project from an assembly job. Every value below carries the formula that produced it and the assumptions it rests on — check them against your own ratings before you use them, because your motor is not this motor.
Nominal 230 V, protection window chosen for appliance ratings
Most Indian appliances are rated 180-260 V. IS 12360 allows the declared LV supply to vary by plus or minus six percent, which is a narrower band than appliances tolerate, so the protection window is set by the appliance, not by the standard.
samples per cycle = fs / f
Averaging over a whole number of cycles is what keeps the RMS figure steady. Ten cycles is 200 ms of data, which is the dominant term in the trip-time budget below.
measurement window + relay operate + contactor operate
Fast enough for sustained over-voltage, which is what damages appliances. It is not surge protection: a lightning-induced spike is over in microseconds and needs an MOV or an SPD, which is a different device and should be stated as out of scope.
I = P / V, then apply the utilisation category
3000 / 230 = 13.0 A. A contactor rated AC-1 for resistive duty must be derated for motor loads, where AC-3 applies, so choosing 25 A for a 13 A load is deliberate margin rather than over-specification.
Set by the compressor's pressure equalisation time
A sealed refrigerant compressor restarted against unequalised pressure stalls and draws locked-rotor current. Three minutes is the delay built into commercial voltage stabilisers for the same reason.
| Item | Qty | Unit cost |
|---|---|---|
Microcontroller board Arduino Nano / ATmega328P | 1 | Rs 250 to Rs 500 |
Voltage sensor module ZMPT101B, 250 V AC input | 1 | Rs 120 to Rs 260 |
Contactor 25 A, 2 pole, 230 V AC coil | 1 | Rs 550 to Rs 1,400 |
Relay module 1 channel, 10 A, opto-isolated | 1 | Rs 80 to Rs 200 |
MCB 16 A double pole | 1 | Rs 220 to Rs 550 |
LCD display 16x2 with I2C backpack | 1 | Rs 140 to Rs 320 |
Setpoint controls Rotary encoder or two potentiometers | 1 | Rs 60 to Rs 180 |
SMPS power supply 5 V, 1 A, enclosed | 1 | Rs 150 to Rs 350 |
Buzzer and indicators Piezo buzzer, panel LEDs | 1 | Rs 40 to Rs 120 |
Enclosure ABS box with DIN rail and cable glands | 1 | Rs 300 to Rs 800 |
Wiring and terminals 2.5 sq mm wire, terminal blocks, lugs | 1 | Rs 200 to Rs 500 |
Test source Variac or dimmer-fed test load for the demo Borrow from the lab if possible — this is usually the largest single cost. | 1 | Rs 900 to Rs 2,600 |
Specifications are written as ratings rather than brands, so any equivalent part works. Where a line says to borrow from the lab, do — it is usually the largest number on the page, and the total drops to Rs 3,473 at the low end without them.
None of these blocks you — they are learnable inside a semester. Each one you do not have costs a couple of weeks, so count them into your plan.
Anything marked required is a blocker, not a difficulty. Arrange the access before you commit to the project, not after.
Use these when your guide says the scope is too small, or when you want something in the results chapter that nobody else in your batch will have.
The structure below is what a project report is marked against, with the mistake that costs marks in each chapter. There is no template to download and there will not be one: the writing is your work, and a site that did it for you would be helping you cheat rather than helping you pass.
A diploma report is typically 40 to 60 pages. The design and results chapters carry the marks; the literature survey can be short. A mini project report runs to about 40 to 50 pages, and the literature survey is usually brief. Guides expect one clear objective, met and measured.
The full report guide — front matter, conventions and page countsOne paragraph covering what the problem is, what you built, and what the result was. Written last, even though it appears first.
Loses marks: Describing the problem and the method but never stating a result. If there is no number in your abstract, it is not finished.
Why the problem matters, the context it sits in, and a clear statement of the objectives your project set out to meet.
Loses marks: Objectives written so vaguely that nobody can tell at the end whether they were met. Write objectives you can tick off in the conclusion.
What has already been done, what each approach achieved, and the specific gap your work addresses.
Loses marks: A list of paper summaries with no comparison and no gap. The survey exists to justify your design choice, so end it by saying what you chose and why.
The system as a whole: the block diagram, what each block does, and the signal or power path between them.
Loses marks: A block diagram copied from a datasheet or another report. Draw yours to match what you actually built, including the parts that are inconvenient.
Every component value and rating, with the formula, the assumptions and the arithmetic that produced it. This is the chapter that distinguishes an engineering project from an assembly job.
Loses marks: Component values with no justification. If a resistor is 10 kOhm, the report must say why it is not 1 kOhm.
The circuit as built, the PCB or wiring, the flowchart, and the parts of the code that carry the actual logic.
Loses marks: Twenty pages of pasted source listing. Include the flowchart and the few functions that matter, and put the full listing in an appendix.
What you measured, in tables and graphs, compared against what you predicted in the design chapter — including where they disagreed.
Loses marks: Photographs of the working model presented as results. A photograph is evidence that it exists, not evidence that it works. Results are measurements.
Whether each objective was met, what the measured performance was, and what the honest next step would be.
Loses marks: Future scope written as a wish list of unrelated features. It should follow from a limitation you actually hit.
Every source in a consistent style, plus datasheets, full code listings and the complete bill of materials.
Loses marks: Citing a blog or a video where a datasheet or a standard exists. Cite the primary source for anything you relied on.
The demonstration is half the assessment. These are the questions this project invites, and the answers are written the way you would give them out loud.
Peak divided by root two is only correct for a pure sine wave. A real distribution feeder carries harmonics from rectifier loads, so the waveform is flat-topped and the peak-derived figure reads low. Squaring, averaging and rooting the actual samples gives the true heating value of the waveform whatever its shape.
Because averaging over a partial cycle weights part of the waveform more than the rest, so the result wobbles from reading to reading depending on where the window happened to start. An integer number of cycles makes the average independent of the start instant.
No, and the report should say so. A surge is over in microseconds while this trips in a couple of hundred milliseconds. Surge protection is a metal oxide varistor or a proper surge protective device that clamps the voltage; this device protects against sustained over and under voltage, which is a different failure mode.
A motor draws the power its mechanical load demands. If the voltage falls, the current has to rise to deliver the same power, and the winding heats as the square of that current. If the voltage falls far enough the motor cannot develop breakaway torque, stalls, and then sits at locked-rotor current until the insulation fails.
A refrigerator or air-conditioner compressor has high-side pressure still standing after it stops. Restarting immediately means starting against that pressure, so the motor cannot break away and draws locked-rotor current. A few minutes lets the pressures equalise through the capillary so the next start is a normal one.
Normally taken as a Diploma project (C-20, 6th sem) or B.E. mini project (5th/6th sem) project. If yours is a different course, the extensions above scope it up and the simpler half of the design scopes it down — the arithmetic does not change. Back to all projects.