8051-Based Fuel-Level Indication and Engine-Temperature Guard for Two-Wheelers

8051-Based Fuel-Level Indication and Engine-Temperature Guard for Two-Wheelers is an embedded-systems project that replaces the wobbling analog fuel needle of a commuter motorcycle or scooter with a stable digital readout, and adds an engine-temperature guard that most 100–150 cc commuter bikes simply do not have. The unit is built around the AT89S52 microcontroller (the 8051 device taught in the M-scheme Microcontroller course), an ADC0808 eight-channel analogue-to-digital converter, the tank's existing float-type fuel sender, an LM35 temperature sensor, a 16x2 LCD, a buzzer and a relay.

The rider sees fuel remaining in litres and in per cent, calibrated for the actual tank shape instead of an arbitrary needle sweep. When the tank reaches reserve (about 1.2 litres on a typical commuter), a low-fuel alert sounds. The LM35, mounted on the cylinder head of our demo rig, drives a two-stage warning: a temperature display with a slow beep at 100 °C, and a relay output that switches a cooling fan on the rig at 105 °C — both with hysteresis so the relay does not chatter.

Because the M-scheme Embedded Systems practical expects a working, tested prototype rather than a paper design, the signal-conditioning circuits are first simulated in NI Multisim / TINA, then breadboarded, calibrated against a measuring cylinder and a water bath, and finally integrated on a veroboard as a bench rig powered from a 12 V battery.

Commuter two-wheelers in India give their riders almost no reliable information about fuel level or engine temperature. The analog fuel needle swings with braking and cornering, sticks with age, and gives no warning before the tank hits reserve, so riders run dry far from a pump. Air-cooled engines carry no temperature indication at all; riders discover overheating only when the engine loses power or seizes, turning a ₹200 coolant or oil-top-up situation into a ₹4,000 rebore. What is needed is a low-cost, programmable digital instrument that reads the tank's existing sender, shows fuel in litres and per cent with a reserve alarm, measures engine temperature, and raises staged alerts with a relay output — all of which a polytechnic student can build and calibrate with the components and skills from the diploma curriculum.

Abstract

Two-wheelers dominate Indian roads, and the commuter segment that most diploma families ride is the worst equipped: many 100–110 cc bikes have no fuel gauge at all, and the ones that do use a bimetallic or float-driven analog needle that swings with cornering, braking and vibration. At the same time, air-cooled engines pushed through city traffic or long ghat climbs overheat with no warning until the engine seizes. This project builds a low-cost digital instrument add-on: an 8051-based fuel-level indicator and engine-temperature guard, simulated, breadboarded and tested as a bench rig.

Introduction

A stranded rider walking to a pump at night is a common scene on Tamil Nadu highways, and a seized engine from overheating is an expensive repair. Both problems are information problems: the rider does not know how much fuel is left or how hot the engine is. Clusters that show these readings cost several thousand rupees and are hard to retrofit; our target is a sub-₹1,500 add-on a diploma student can build, calibrate and demonstrate.

Existing System

• Fuel level is shown by an analog needle driven by the tank's float sender; it swings, sticks and gives no reserve alarm beyond a blinking lamp on some models.
• Most commuter bikes have no engine-temperature indication; a red oil lamp appears only after oil pressure is already lost.
• The float sender's resistance is nonlinear across the tank, so a simple linear circuit reads wrong in the middle of the tank.
• Limitations: no numeric reading, no programmable alert thresholds, no temperature sensing, and no record of what the readings were.

Proposed System

• Read the existing float sender (about 10–180 Ω across our reference tank) through a divider and the ADC0808, and display fuel in litres and per cent on a 16x2 LCD, corrected by a measured calibration lookup table.
• Read an LM35 fitted to the cylinder-head area of the demo rig and display temperature in °C with about 1 °C resolution.
• Two-stage guard: warning (slow beep + indicator) at 100 °C, alert (continuous buzzer + relay) at 105 °C with 4 °C hysteresis; the relay drives a cooling fan on the rig to prove the output stage safely.
• Low-fuel alert with blinking display when the tank reaches reserve (1.2 L).
• Sensor-fault detection: an open or shorted sender shows an error code instead of a wrong reading.
• Runs from the vehicle's 12 V battery through a 7805-based supply tested over 11–14.5 V.

Feasibility Study

• Technical: every block — ADC interfacing, LCD, relay driving and Embedded C programming — is covered by the 34052 Microcontroller and 34066 Embedded Systems practical courses; the circuit is first proved in Multisim / TINA simulation.
• Economic: the bill of materials works out to roughly ₹1,100–₹1,700, and many parts are already available in the college lab.
• Operational: the unit uses the bike's own sender, needs no tank modification, and the demo rig keeps the workbench safe.

In scope

• A single-vehicle bench demo rig: fuel sender emulated first with a 220 Ω potentiometer and then with the actual tank unit salvaged from the college's scrap commuter bike.
• Fuel display (0–10 litres, per cent), reserve alert at 1.2 L, temperature display, two-stage over-temperature alert, relay-driven cooling fan on the rig.
• Calibration tables, error-code handling, and a 12 V-to-5 V regulated supply tested over the bike battery's real voltage range.

Out of scope (v1)

• No wiring to a running engine and no ignition cut-off — safety and road-worthiness rules both forbid it at diploma level; the guard is proved on the rig.
• No speedometer, odometer or mileage calculation.
• No Bluetooth app, GPS tracking or fuel-theft detection (listed under future scope).
• No injection-controlled or CNG-variant engines.

The project follows a phased build-and-test plan rather than a pure software SDLC, because every stage ends with a measurable hardware result. Reviews are timed to the M-scheme schedule: Review I after the design phase, Review II after the working breadboard.

Testing approach: every sensor chain is verified against a known reference before firmware trusts it — known voltages for the ADC, a measuring cylinder for fuel, a water bath against a lab thermometer for temperature. Alert behaviour is tested at the boundaries (1.3 L, 1.1 L, 99 °C, 101 °C, 104 °C, 106 °C) and recorded in a test-case table with expected and observed results.

The unit is a classic sensor → converter → controller → output embedded system, organised as four blocks around the AT89S52.

flowchart LR
  B["12 V vehicle battery"] --> PS["7805 regulated 5 V supply"]
  F["Float fuel sender (10–180 ohm)"] --> C1["Divider: 470 ohm + sender, RC filter"]
  T["LM35 on cylinder head"] --> C2["RC filter and buffer"]
  C1 -->|"CH0"| A["ADC0808, Vref 2.56 V"]
  C2 -->|"CH1"| A
  PS --> A
  A -->|"8-bit data, EOC handshake"| U["AT89S52 (8051)"]
  PS --> U
  U --> L["16x2 LCD (HD44780)"]
  U --> Z["Buzzer"]
  U --> D["ULN2003 driver"] --> RY["12 V SPDT relay"] --> FN["Cooling fan on demo rig"]

Sensing block. The float sender forms the lower leg of a divider fed from 5 V through a 470 Ω resistor, so a full tank (low resistance, about 10 Ω) reads near 0.1 V and an empty tank (about 180 Ω) reads near 1.4 V — safely inside the ADC's 2.56 V span and inverted in firmware. An RC filter removes the sender's noise; the LM35 output is filtered and buffered before CH1.

Conversion block. The ADC0808 is chosen because the 8051 has no on-chip ADC. Its Vref(+) is set to 2.56 V with a TL431 reference so that one LSB = 10 mV, which matches the LM35's 10 mV/°C scale exactly — one count is one degree. Channel selection is on ADDA/ADDB/ADDC, and the ALE/START and EOC lines handshake with the controller.

Control block. Firmware in Embedded C averages eight samples per channel, converts fuel counts through the lookup table and temperature counts directly in °C, refreshes the LCD every 500 ms, and evaluates the alert rules with hysteresis.

flowchart TD
  S["Main loop (every 500 ms)"] --> R["Read CH0 and CH1, average 8 samples"]
  R --> C["Convert: fuel via lookup table, temp in deg C"]
  C --> D["Update LCD: litres, per cent, temperature"]
  D --> Q1{"Fuel below reserve?"}
  Q1 -->|Yes| A1["Blink fuel field, short beep"]
  Q1 -->|No| Q2
  A1 --> Q2{"Temp above 105 deg C?"}
  Q2 -->|Yes| A2["Continuous buzzer, relay energised"]
  Q2 -->|No| Q3{"Temp above 100 deg C?"}
  Q3 -->|Yes| A3["Warning indicator, slow beep"]
  Q3 -->|No| S
  A2 --> S
  A3 --> S

Output block. Port pins drive the buzzer directly and the relay through the ULN2003 Darlington array with a flyback diode, so the inductive load never stresses the controller.

• Add a 24C02 EEPROM to log fuel and temperature history, enabling a mileage estimate per trip.
• Bluetooth (HC-05) link to a phone app so the rider sees readings and alerts without looking down at the cluster.
• Ultrasonic fuel sensing for tanks where a float cannot be fitted (CNG dual-fuel kits, custom tanks).
• Digital speedometer and odometer from a Hall sensor on the wheel, completing a full cluster.
• Fuel-theft alert: a sudden fuel drop while the ignition is off sends a warning via GSM.
• Proper two-layer PCB and an ABS enclosure so the unit can be fitted to a college demonstration vehicle.