Digital Thermometer

Work in progress...

I built this circuit on the breadboard last fall and wrote some code for a micro controller to convert the analog temperature readings into a digital format on a LED screen, but the code for the LED screen is tedious and my time precious. The circuit works and the temperature reading are accurate over a range from freezing to boiling in degrees Fahrenheit. Once I get some free time, I'll put pictures up of the construction process for assembling the components onto a stripboard (Veroboard) with details explaining how the components work in conjunction with one another.

The two potentiometer (rheostats) allow you to calibrate the circuit so that the temperature readings are accurate. When the circuit is constructed on the stripboard, I think I will use smaller, board mountable, potentiometers so that as the components degrade, I can still adjust the performance instead of just using a single resistance in its place.

The clear tube with the black end is actually a straw with a transistor inside. A portion of the transistor is sticking out the end of the straw with the legs sealed from the outside, so that I could dip it into extremes of boiling water and ice water to aid in calibration. I'm well aware that you can buy a cheap thermometer, but I thought it would be cool to explore the aspects of the transistor. The theory is that if the current is kept constant through the transistor, then the voltage will vary linearly with the temperature. Thus, it is just a matter of reading the voltage and applying a scaling quantity to equate it to the temperature.

I know the circuit on the board is messy, but it was put together hastily just to ensure that the design worked.