This was my first electronics project which I completed whilst at high school. The gadget takes input from a K-Type thermocouple and displays absolute temperature on a 16×2 character LCD.
The project came about from my love of overclocking at the time where I was using liquid nitrogen to cool my computer. My shop-bought meter had broken so I created my own with a display that was easier to read from a distance. I used both lines of the LCD to display tall numbers to achieve this. The gadget is powered from a standard DC wall adapter to avoid the need for replacing batteries as it is designed to operate for long periods of time.
A PIC microcontroller is used to drive the LCD. It reads the analogue output of an off-the-shelf thermocouple amplifier which takes care of cold-junction compensation. The simple circuit is mounted on a home-etched PCB.