A prepaid meter reverses the billing cycle: the consumer pays first and the meter counts the balance down as energy is used, disconnecting the supply when it reaches zero. This project measures energy with a calibrated metering front end, converts each pulse into rupees at a stored tariff, holds the balance in non-volatile memory so a power cut cannot erase it, warns the consumer over SMS as the balance runs low, and disconnects through a latching relay that draws no holding current.
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 2,770 to Rs 7,000 |
Spares and replacements 15 % — you will destroy something | Rs 416 to Rs 1,050 |
Consumables and hardware Wire, connectors, headers, screws, heatshrink | Rs 332 to Rs 840 |
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 4,068 to Rs 10,490 |
| Each, split 3 ways | Rs 1,356 to Rs 3,497 |
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 3.5 week figure assumes 8 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 metering front end produces a fixed number of pulses per kilowatt hour. Each pulse is therefore a known quantity of energy, and the controller only has to count them.
On every pulse the controller subtracts the cost of that much energy from the stored balance, using a tariff held in memory that can be edited rather than being hard-coded.
The balance is written to non-volatile memory, but not on every pulse — flash and EEPROM have finite write endurance, so the value is committed on a change of a set size and on a power-fail interrupt.
When the balance falls below a warning threshold the module sends an alert. When it reaches zero the controller pulses the latching relay to open and the load is disconnected.
A recharge arrives as an SMS or a web request with a token, the controller adds the amount to the balance and pulses the relay back closed.
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.
Energy per pulse = 1 / (pulses per kWh)
3200 impulses per kilowatt hour is the standard rate marked on Indian domestic meters. 1000 Wh divided by 3200 gives 0.3125 Wh per pulse.
cost per pulse = tariff / (pulses per kWh)
6.50 divided by 3200. The tariff is an editable setting, not a constant — state slabs are revised most years, and a meter with last year's tariff burned into the firmware is wrong by definition.
Balance held in paise as an integer, not rupees as a float
Repeatedly subtracting 0.00203 from a 32-bit float accumulates rounding error over tens of thousands of pulses. Hold the balance as an integer number of paise, or better as an integer count of pulses, and convert to rupees only for display.
Standing loss = coil power x hours
0.4 W times 8760 hours is 3504 Wh. A latching relay takes a pulse to change state and nothing to hold it, so the meter does not spend a measurable part of the consumer's own supply keeping itself connected.
I = P / V, sized for the sanctioned load
4000 / 230 = 17.4 A. Domestic sanctioned loads are usually a few kilowatts; size for the sanctioned load, not the connected load.
| Item | Qty | Unit cost |
|---|---|---|
Microcontroller board ESP32 or Arduino Nano | 1 | Rs 250 to Rs 700 |
Energy metering module PZEM-004T v3.0 with CT, or an ADE7757 based board | 1 | Rs 600 to Rs 1,400 |
GSM module SIM800L with a 2 A supply, or use the ESP32 WiFi instead Skip this if you use WiFi and a web dashboard — it is the largest optional cost. | 1 | Rs 450 to Rs 1,100 |
Latching relay 30 A, dual coil, 12 V | 1 | Rs 280 to Rs 750 |
External EEPROM or FRAM AT24C256 or FM24C04 on I2C | 1 | Rs 60 to Rs 220 |
LCD display 16x2 with I2C backpack | 1 | Rs 140 to Rs 320 |
Keypad 4x4 matrix membrane | 1 | Rs 70 to Rs 180 |
SMPS power supply 5 V and 12 V, 2 A | 1 | Rs 200 to Rs 480 |
MCB 16 A double pole | 1 | Rs 220 to Rs 550 |
Enclosure ABS meter box with a clear window | 1 | Rs 300 to Rs 800 |
Wiring and terminals 2.5 sq mm wire, terminal blocks, lugs, ferrules | 1 | Rs 200 to Rs 500 |
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 4,068 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.
The metering front end multiplies instantaneous voltage by instantaneous current and integrates the product over time, which is energy. It expresses the result as a train of pulses at a fixed number per kilowatt hour, so counting pulses is counting energy. The controller never has to do the multiplication itself.
It is the meter constant: the pulse output emits 3200 pulses for every kilowatt hour that passes through it. One pulse is therefore 1000 divided by 3200, which is 0.3125 watt hours. It is what lets you check a meter's accuracy by timing pulses against a known load.
Because floating point cannot represent most decimal fractions exactly, so subtracting a small amount tens of thousands of times accumulates error in one direction. Holding paise, or pulses, as an integer makes every subtraction exact and the total auditable.
An ordinary relay needs coil current for as long as it is closed, which for a meter is permanently, and that power is drawn from the consumer's own supply. A latching relay uses a pulse to change state and holds mechanically, so the standing loss is zero. It also survives a controller reset without dropping the load.
Revenue is collected before supply rather than after, so there is no arrears cycle and no disconnection crew. Consumption also tends to fall, because the consumer sees the balance falling in real time rather than a bill a month later. The trade-offs are the cost of the meter and the harder problem of ensuring supply is not cut off from someone who cannot recharge.
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.