Water Level Detector
Team EN-14 BROVO6 · Department of Electronic & Telecommunication Engineering, University of Moratuwa · October 2022
Module lecturer: Mr. Ajith Pasqual
Problem & Solution
Problem
Household water tanks — often located on rooftops or at the back of the property — are hard to monitor. Forgetting to switch off the pump causes water overflow (wastage), power wastage, motor winding damage, and well-water depletion. During Sri Lanka's 2022 power cuts, knowing the water level in advance allowed residents to refill before the blackout. A user survey (n = 91.7% agreement) validated the need for a mobile alert system.
Solution
A compact IoT device mounted on the inside of the tank lid uses an HC-SR04 ultrasonic sensor to measure the air gap between the sensor and the water surface. The ATmega328P calculates the water level percentage using:
The result is transmitted via HC-06 Bluetooth to a custom Android app. Notifications are sent when the level drops below 15% (low — alert to refill) or rises above 95% (overflow — alert to switch off pump). The user can also set the tank volume for volumetric display (optional).
Technical Specifications
| Microcontroller | ATmega328P (28-SPDIP) — 8-bit RISC, 32KB Flash, 2KB SRAM |
| Distance Sensor | HC-SR04 Ultrasonic (2 cm – 400 cm, ±3 mm) |
| Wireless | HC-06 Bluetooth (≤ 100 m, 2.4 GHz FHSS, up to 2.1 Mb/s) |
| Clock | 16 MHz Crystal Oscillator |
| Power | 7.5 V battery → LM7805 → 5 V regulated (rechargeable) |
| PCB Size | 55 mm × 53 mm (Altium Designer) |
| Enclosure | 125 mm × 75 mm × 40 mm (SolidWorks) |
| Weight | ≈ 468 g |
| Power Consumption | ≈ 695 mW total |
| Alert Threshold (low) | Below 15% water remaining |
| Alert Threshold (high) | Above 95% water level (overflow warning) |
| Total Budget | 7,752 LKR |
Hardware Design
Circuit & PCB (Altium Designer)
The 7.5 V battery is regulated to 5 V by an LM7805. Two smoothing capacitors reduce ripple. A 4-pin header connects to the HC-SR04 ultrasonic sensor; another 4-pin header connects to HC-06. A voltage divider (220Ω + 470Ω) drops the 5 V TX signal to 3.3 V for the HC-06 RX pin. A LED and on/off switch are included on the board. The 16 MHz crystal provides the ATmega328P clock. PCB: 55 mm × 53 mm, trace width 8.5 mm (power), clearance 0.85 mm, hole size 0.85 mm.
Enclosure (SolidWorks)
125 mm × 75 mm × 40 mm two-part plastic enclosure. Top casing has two round holes for the ultrasonic sensor's transmit/receive transducers, holes for the LED and switch, and four 3 mm × 20 mm holes to bolt the two halves together. Base casing has four 3 mm × 5 mm standoffs to mount the PCB, and four external holes to fix the device to the tank lid.
Mobile App & UI
A custom Android application connects to the HC-06 Bluetooth module. Setup steps:
- Install the app and pair Bluetooth with HC-06.
- Open the app and connect to HC-06.
- With tank empty, press Set Tank Height to calibrate the zero reference.
- Optionally enter the tank volume for litre-based display.
- Live percentage is shown on the home screen and as push notifications.
- Alerts fire below 15% (low) and above 95% (overflow).
The app UI features a clear percentage gauge and a notification toggle. Data is polled every 1.5 s from the sensor and streamed via Bluetooth serial at 9600 baud.
Firmware (ATmega328P — Arduino)
The firmware triggers the HC-SR04 (10 µs TRIG pulse), measures the echo pulse width via pulseIn(), divides by 58 to get distance in cm, and transmits it via HC-06 at 9600 baud every 1.5 s. The app computes the water percentage from the received distance and the calibrated tank height.
Budget (Total: 7,752 LKR ≈ export price 8,000 LKR)
| Item | Qty | Total (LKR) |
|---|---|---|
| ATmega328P Microcontroller | 1 | 2,000 |
| Ultrasonic Sensor HC-SR04 | 1 | 250 |
| Bluetooth Module HC-06 | 1 | 900 |
| 16 MHz Crystal Oscillator | 1 | 25 |
| Rechargeable Battery | 1 | 1,000 |
| LED | 1 | 2 |
| On/Off Switch | 1 | 20 |
| Air Suckers (mounting) | 2 | 50 |
| Pin headers (4-pin × 2, 2-pin × 2) | 4 | 120 |
| Capacitors (0.33 µF, 0.11 µF, 22 pF × 2) | 4 | 90 |
| Resistors (220 Ω × 2, 470 Ω × 1) | 3 | 25 |
| PCB Fabrication | 1 | 500 |
| Enclosure (SolidWorks + print) | 1 | 2,800 |
Results & Challenges
The final device successfully measured the water level in a tank and displayed the percentage on the Android app in real time. Push notifications for low and overflow states were verified.
Key challenges overcome:
- Confirming ultrasonic reflection off a water surface — initially uncertain, ultimately verified experimentally.
- Finding a Bluetooth module with ≥ 100 m range (HC-06 supports up to 100 m vs. typical 10 m modules).
- Enclosure dimensions and waterproofing for outdoor/tank-lid installation.
- PCB design under limited prior experience with Altium's routing rules.
