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2-Digit Digital Thermometer

A low-cost, analog 2-digit digital thermometer designed to measure temperatures from 0 °C to 99 °C. This project was developed for the IE2044 – System Modelling and Prototyping module using an LM35 temperature sensor, a TC7107 ADC/display driver, and dual seven-segment displays.

📌 Project Overview

The thermometer converts the LM35 sensor output directly into a temperature reading without using a microcontroller or firmware. Since the LM35 produces 10 mV/°C, the circuit is calibrated so that each degree Celsius corresponds to one displayed count.

The design combines:

• An LM35 precision temperature sensor
• A TC7107 / ICL7107 analog-to-digital converter and display driver
• Two common-cathode seven-segment displays
• A calibrated 100 mV reference voltage
• Analog star-point grounding to reduce display jitter and noise
• Visual indication for temperature overflow and underflow conditions

✨ Key Features

• Measurement range: 0 °C to 99 ��C
• Direct voltage scaling: 10 mV from the LM35 represents 1 °C
• Reference calibration: 100 mV using a 1 kΩ trimmer potentiometer
• No microcontroller required: Fully analog measurement and display chain
• Overflow indication: Red LED for temperatures above 99 °C
• Underflow indication: Green LED for temperatures below 0 °C
• Noise reduction: Analog star-point grounding using ADND*
• Dual-supply operation: +5 V and −5 V rails
• PCB design: Single-layer routing with SMD 0805 components

🧠 Operating Principle

The LM35 generates an output voltage proportional to the measured temperature:

VLM35 = 10 mV × Temperature (°C)

For example:

25 °C → 250 mV
75 °C → 750 mV

The TC7107 measures this analog voltage and drives the two seven-segment displays. With the reference voltage calibrated to 100 mV, the displayed value corresponds directly to the temperature in degrees Celsius.

🛠️ Component Summary

📁 Repository Contents

Digital-2-Digit-Thermometer-/
├── Diagrams/               # System block diagrams and architecture diagrams
├── Report/                 # Final project report
├── Schematics/             # Proteus simulation files and EasyEDA PCB sources
├── SMP final project.pdf   # Official module project brief and specifications
└── README.md               # Project documentation

🧪 Simulation and PCB Implementation

Phase I — Simulation

The circuit was tested in Proteus Design Suite 8.06 across the complete 0 °C to 99 °C operating range. The simulation also validates:

• Normal temperature measurements
• Overflow conditions above 99 °C
• Underflow conditions below 0 °C
• Seven-segment display operation
• LED error indication
• Reference-voltage calibration

Phase II — PCB Design

The PCB was developed using EasyEDA Pro with the following design requirements:

• Single-layer routing
• SMD 0805 resistor and capacitor footprints
• Analog star-point grounding
• Reduced digital switching noise
• Horizontally aligned seven-segment displays
• Layout suitable for practical assembly and testing

🔌 Power Requirements

The design uses a dual-supply configuration:

Safety note: Verify the power-supply polarity and voltage levels before connecting the circuit. Incorrect supply connections may damage the TC7107, LM35, displays, or other components.

👥 Project Team

Module: IE2044 – System Modelling and Prototyping
Academic Year: Year 2, Semester 2
Institution: Sri Lanka Institute of Information Technology (SLIIT)
Group: 05

📚 Technologies and Tools

• Proteus Design Suite 8.06 — Circuit simulation
• EasyEDA Pro — Schematic capture and PCB design
• LM35 — Analog temperature sensing
• TC7107 / ICL7107 — ADC and seven-segment display driving

📄 License

This project was created for academic and educational purposes as part of the IE2044 module.