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The problem
Community water ATMs — coin or token operated RO-water kiosks — are common across Indian towns and housing clusters, yet the operator's side of the business is still cash-in-a-box. Coins jam the acceptor, unattended sales go unrecorded, and nobody knows how much water a kiosk actually dispensed on a given day. When the tank runs dry or a regular complains about a short fill, there is no log to check. This project replaces the cash box with prepaid RFID cards and a cloud log. A user taps a registered card, selects a volume preset on the LCD, and the ESP32 dispenses exactly that much water through a solenoid valve while a Hall-effect flow sensor meters every litre. The fare is deducted from the card's stored balance, and every transaction — card ID, volume, timestamp, remaining balance — is pushed over Wi-Fi to the operator's dashboard. The operator sees revenue, daily volumes, low-balance cards and tank level from anywhere, while the kiosk keeps dispensing on card balance even when the internet drops.
Taps the RFID card on the reader, picks a volume preset on the LCD menu and confirms the fare.
Follow the working sequence
How it works
- The operator registers RFID cards from the kiosk admin menu and tops each one up with prepaid credit, stored in the card's value block.
- A user taps a card on the RC522 reader; the ESP32 authenticates the UID against its registered list and reads the balance.
- The LCD shows the balance and the user picks a volume preset (1, 2, 5, 10 or 20 litres); the ESP32 computes the fare at the configured ₹-per-litre rate and verifies the balance covers it.
- On confirmation the ESP32 energizes the 12V solenoid valve through a relay and water flows through the YF-S201 flow sensor toward the tap.
- The sensor's Hall pulses (approx. 450 per litre, datasheet) are counted on an ESP32 interrupt pin; when the count reaches the target volume the valve is de-energized.
- The fare is deducted, the new balance is written back to the card, and the LCD confirms the dispensed volume with the remaining balance.
- A JSON transaction record (card ID, volume, timestamp, remaining balance) is published over Wi-Fi via MQTT or HTTP to the cloud dashboard for the operator.
Tech stack:
- ESP32-WROOM-32 (Arduino core, Wi-Fi uplink)
- RC522 RFID reader · MIFARE Classic 1K cards
- YF-S201 Hall-effect flow sensor
- 12V solenoid valve · relay driver
- 16x2 LCD · pushbutton menu
- HC-SR04 ultrasonic sensor (tank level)
- MQTT · HTTP JSON (cloud logging)
- Operator dashboard (HTML · CSS · JS)
| Parameter | Value |
|---|---|
| Controller | ESP32-WROOM-32, 240 MHz dual-core (datasheet) |
| RFID reader | RC522, 13.56 MHz, MIFARE Classic 1K cards (datasheet) |
| Flow sensor | YF-S201, approx. 450 pulses/litre (datasheet) |
| Dispense accuracy | ±10% of volume, uncalibrated (datasheet); buyer-run calibration routine included |
| Volume presets | 1 / 2 / 5 / 10 / 20 litres (menu-selectable) |
| Solenoid valve | 12V DC, 1/2-inch port (design target) |
| Tariff | ₹5 per 20 litres, configurable (design target) |
| Cloud uplink | Wi-Fi 802.11 b/g/n; MQTT or HTTP JSON (design target) |
| Offline queue | Approx. 500 transaction records in flash (design target) |
| Power | 12V 2A adapter with 5V buck for logic (design target) |
Project features
- [RFID prepaid card billing] An RC522 reader authenticates MIFARE Classic cards by UID against the kiosk's registered list and reads the stored balance from a card value block — no coins and no cash handling at the machine.
- [Pulse-metered dispensing] The ESP32 drives the 12V solenoid valve through a relay and counts YF-S201 Hall pulses (approx. 450 pulses per litre, datasheet value) on a hardware interrupt, closing the valve the moment the selected volume is reached.
- [Volume menu with fare preview] A 16x2 LCD plus two pushbuttons offers 1/2/5/10/20-litre presets; the fare at the configured rate is shown before the user confirms, and the balance is checked against it.
- [Balance write-back] After each dispense the fare is deducted and written back to the card, and the LCD shows the dispensed volume with the remaining balance — the card itself is the receipt.
- [Cloud transaction log] Every dispense publishes a JSON record (card ID, volume, timestamp, remaining balance) over Wi-Fi via MQTT or HTTP; records queue locally when offline and sync on reconnect.
- [Operator dashboard] A live dispense feed, daily volume and revenue totals, per-card balances with low-balance flags, kiosk online/offline status and a tank-level indicator — a working single-file demo of the dashboard is included.
- [Tank-level alerting] An ultrasonic sensor watches the source tank and the dashboard flags low water so the operator refills before the kiosk runs dry. (Optional: GSM SMS fallback for the alert. Future scope: UPI-based card recharge.)
What is included
- Assembled kiosk prototype (ESP32, RC522, YF-S201, solenoid valve, LCD, tank, dispensing tap)
- ESP32 firmware (card authentication, pulse metering, valve control, MQTT/HTTP logging, offline queue)
- Cloud operator dashboard (live log, daily totals, per-card balances, tank status)
- Working single-file dashboard demo
- Flow-sensor calibration procedure (measuring-jug method)
- Project report PDF (background, design, methodology, results)
- PPT presentation for final review
- Viva Q&A preparation document
Limitations & prerequisites
- The YF-S201 is rated ±10% (datasheet) uncalibrated; the included calibration routine tightens this, but billing-grade accuracy needs a certified meter.
- With no internet there is no live cloud log — the kiosk keeps dispensing on card balance and queues approx. 500 records locally, syncing when Wi-Fi returns.
- MIFARE Classic cards are clonable with cheap tools, which is acceptable for a campus prototype but not for real-money deployment.
- The solenoid valve is on/off only, so flow rate follows inlet pressure (approx. 0.5–2 L/min from a gravity tank, expected); weak pressure means slow dispenses.
- Balance lives on the card itself, so a lost card loses its credit — there is no central account recovery in the base build.
- Tank sensing is a single low-water alert point, not a continuous level gauge, in the base build.
Frequently Asked Questions
How does the kiosk measure the water it dispenses?
The YF-S201 Hall-effect flow sensor emits approx. 450 pulses per litre (datasheet value); the ESP32 counts them on a hardware interrupt and shuts the 12V solenoid valve when the count matches the selected volume. The build ships with a calibration routine the buyer runs once against a measuring jug to tighten the ±10% uncalibrated figure.
What happens if the Wi-Fi drops during a dispense?
Nothing breaks: dispensing, fare deduction and the card write-back all run locally on the ESP32. The transaction record is queued in flash (approx. 500 records) and pushed to the cloud dashboard when the connection returns — only the live log pauses.
How are cards recharged?
From the kiosk's admin menu: the operator taps a card, enters an amount, and the new balance is written to the card's value block. UPI-based self-recharge is listed as future scope.
Can the tariff be changed?
Yes — the ₹-per-litre rate is a configuration value (default ₹5 per 20 litres, design target) changeable from the admin menu, so the operator can reprice all presets without touching the firmware.
How is this different from a prepaid water meter for a house?
A household prepaid meter sits on a home's pipeline and cuts supply when credit runs out. This is a public dispensing kiosk: walk-up users tap a card, choose a volume and fill a container, while the operator watches every sale on a dashboard. Different device, different buyer.
Is this project suitable for a final-year project?
Yes — for Electronics, E&TC and IoT/Embedded programs. It combines embedded firmware, sensor interfacing, power switching, RFID basics and a cloud dashboard, with honest calibratable measurement and a clear real-world operator story for the viva.
Components & software requirements
- ESP32-WROOM-32 (Arduino core, Wi-Fi uplink)
- RC522 RFID reader · MIFARE Classic 1K cards
- YF-S201 Hall-effect flow sensor
- 12V solenoid valve · relay driver
- 16x2 LCD · pushbutton menu
- HC-SR04 ultrasonic sensor (tank level)
- MQTT · HTTP JSON (cloud logging)
- Operator dashboard (HTML · CSS · JS)
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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