This project gives you a nice and simple scientific calculator using AVR microcontroller. It has 2 keypads as shown in the circuit diagram and the results are shown on the 16×2 LCD display. You can do sin,cos, tan functions using this project.
The code is written in Codevision AVR C. You can download the codevision project file and also the proteus simulation file.
For more Detail: Scientific Calculator using AVR Microcontroller