Digital Fuel Gauge using Ultrasonic Sensor and Arduino

A digital fuel gauge using an ultrasonic sensor and Arduino measures how much liquid sits in a tank without any part touching the liquid, which is the problem with the float-arm gauges fitted in most vehicles: the moving arm wears, sticks and drifts, and the dashboard needle gives only a rough idea of what remains. This project replaces that float with a waterproof JSN-SR04T ultrasonic sensor mounted above the liquid, an Arduino Uno that converts echo time into distance and then into litres, and a 16x2 LCD that shows the level as litres, a bar graph and a low-fuel buzzer alert. The demo runs on a model tank filled with water, never real petrol, so the principle can be shown safely in a college lab. Choosing the waterproof sensor is the central engineering decision: the common HC-SR04 module is not waterproof and must never be mounted inside a fuel tank, while the sealed JSN-SR04T probe is made for wet environments.

The digital fuel gauge works as a chain of four conversions: sound into distance, distance into litres, litres into a display, and a low level into an alert. The JSN-SR04T probe above the tank sends a short 40 kHz ultrasonic pulse downward and listens for the echo bouncing off the liquid surface. The Arduino measures the echo travel time and converts it to distance with the relation distance = echo time x speed of sound / 2, halving because the sound travels down and back. That distance is mapped to litres using the two calibration points recorded for the empty and full tank, so the reading reflects the actual tank rather than a guessed formula. Finally the Arduino writes litres and a bar graph to the 16x2 LCD and sounds the buzzer when the level drops below the set threshold.

1. The JSN-SR04T waterproof probe is mounted at least 25 cm above the highest liquid level in the model tank, facing straight down at the surface.
2. The probe sends a 40 kHz ultrasonic pulse and the Arduino measures how long the echo takes to return from the liquid surface.
3. The Arduino converts echo time to distance using distance = echo time x speed of sound / 2, with the speed of sound taken as approximately 343 m/s at room temperature.
4. The distance is mapped to litres using the two-point calibration (empty distance and full distance) recorded with known volumes of water.
5. The 16x2 LCD displays the level in litres with a bar graph, and the firmware averages several echoes so ripples do not make the reading jump.
6. When the level falls below the configurable low-fuel threshold (approximately 20% of capacity), the buzzer sounds until the tank is refilled.

Fuel sensing comparison

Tech stack:

• Arduino Uno (ATmega328P)
• JSN-SR04T waterproof ultrasonic sensor
• 16x2 character LCD
• Arduino IDE · C/C++ firmware
• Breadboard · jumper wires
• 5 V DC power supply
• Piezo buzzer
• Model tank · water demo setup

The digital fuel gauge is built around four capabilities that work together: waterproof ultrasonic level sensing that never touches the liquid, a two-point tank calibration that turns raw distance into honest litres, a clear LCD readout with a bar graph, and a low-fuel buzzer that warns before the tank runs dry. A fifth capability, echo averaging, steadies the reading when the liquid surface ripples, and a sixth, dead-zone aware mounting, keeps the sensor in its valid measuring range at every level. The whole instrument is a static tank device with no motors, no chassis and no movement of any kind: it measures, calibrates and displays, which is precisely what separates it from navigation builds that happen to use the same sensor and controller. It runs offline on a simple 5 V supply with no internet and no float to wear out.

• [Waterproof ultrasonic level sensing] A sealed JSN-SR04T probe mounted above the liquid measures the distance to the surface with 40 kHz sound pulses, so no sensor part ever contacts fuel or water.
• [Litres readout with bar graph] The 16x2 LCD shows the level in litres alongside a bar graph, so the reading is useful at a glance during a demonstration.
• [Two-point tank calibration] Empty and full distances are recorded once with known volumes, and the firmware maps every later distance to litres between those two points.
• [Low-fuel buzzer alert] A buzzer sounds when the level falls below a configurable threshold (approximately 20% of tank capacity), giving an audible warning before the tank empties.
• [Echo averaging for steady readings] The firmware averages several echoes and rejects stray readings, so ripples on the liquid surface do not make the display jump.
• [Dead-zone aware mounting] The sensor is mounted at least 25 cm above the highest liquid level, respecting the JSN-SR04T blind zone so readings stay valid across the full tank.
• [Safe model-tank demonstration] The demo uses a model tank filled with water, never real petrol, with the sensor mounted above the liquid at all times.

• Working digital fuel gauge prototype (Arduino, JSN-SR04T probe, LCD, buzzer, model tank)
• Arduino firmware with calibration and averaging logic
• Circuit and wiring documentation with connection table
• Two-point tank calibration procedure with worked example
• Project report PDF (background, ultrasonic theory, methodology, calibration, results)
• PPT presentation for final review
• Viva Q&A preparation document (ultrasonic ranging, calibration, sensor selection)