The Dual-Mode Analog Thermometer is a precision temperature measurement device designed using analog components to ensure high accuracy and reliability. Unlike fully digital thermometers, this design utilizes thermistors, Wheatstone bridges, and an instrumentation amplifier for precise temperature readings.

This project was developed as part of the EN2091 Laboratory Practice and Projects module in our 3rd semester, focusing on hands-on circuit design, sensor integration, and analog signal processing.

✅ Dual-Mode Functionality – Toggle switch to switch between body temperature and liquid temperature modes.
✅ High Accuracy – Uses thermistors, Wheatstone bridges, and an instrumentation amplifier for precise readings.
✅ OLED Display – Temperature readings are displayed on an OLED screen, with an Arduino used solely for display purposes.
✅ Stable Power Supply – Converts AC to +10V, -10V, and 5V for reliable operation.
✅ Future Expansion – Plans to integrate a MUX for additional modes.

• Circuit Simulation: 🖥️ LTspice
• Schematic & PCB Design: 🖊️ Altium Designer
• Enclosure Modeling: 📐 SolidWorks

We designed both the schematic and printed circuit boards (PCBs) using Altium Designer. The project includes:

• 🧠 Main Thermometer PCB – Houses the signal conditioning circuit using Wheatstone bridges, thermistors, and an instrumentation amplifier.
• 🔋 Dual Power Supply PCB – Converts AC input into stable +10V, -10V, and 5V DC outputs.

Complete circuit schematic designed in Altium Designer.

Main PCB for the analog thermometer circuit.

Power supply PCB providing +10V, -10V, and 5V rails.

To protect and house the electronics, we created a cost-effective 3D-printed enclosure using SolidWorks. The design features:

• 💡 Compact & Ergonomic layout for portability and ease of use.
• 🛠️ Snap-fit joints for quick assembly without screws.
• 🔄 Modular access to switch between body and liquid temperature modes.
• 📏 Display window for OLED visibility and button access.

3D-modeled enclosure designed for compactness and cost-efficient 3D printing.

• Components: Thermistors, Wheatstone bridge circuit, instrumentation amplifier, Arduino, OLED display
• Software: LTspice, Altium Designer, SolidWorks, Arduino IDE

1. Assemble the Circuit using the schematic provided.
2. Program the Arduino with the provided firmware.
3. Power the System using a +10V, -10V, and 5V power supply.
4. Use the Toggle Switch to switch between temperature modes.
5. Observe the Temperature Readings on the OLED display.

• Luchitha Perera
• Benul Wijayarathna
• Sanugi Wickramasinghe
• Hansani Kaumadi