Hello friends! Today, we are going to design a simple calculator with an 8051 microcontroller in Proteus. We will combine a 4×4 keypad, a 20×4 LCD and an AT89C51 so that you can enter an arithmetic operation and see its result on the display. We have already covered LCD interfacing and keypad interfacing with the 8051 . Those lessons provide the input and output functions. Here, we will add the application logic that decides which key is valid and when a calculation should take place. This remains a single-digit calculator, like the original project. It accepts two operands from zero through nine and supports addition, subtraction, multiplication and integer division. We will also handle negative results, invalid input and division by zero explicitly. Figure: Original 8051 calculator showi ...