A block diagram is a diagram of a system in which the principal parts or functions are represented by blocks connected by lines that show the relationships of the blocks. Block diagrams are heavily used in engineering in hardware design like open-door systems, software design, and process flow diagrams. The mechanism of the electronic door system can be illustrated using a block diagram that shows which sensors get activated when someone enters the desired passcode to enter the room. The block diagram shows Microcontroller PIC16F877A, which takes data from the PIR sensor and keypad. The door open system also has an NFC shield which is a Near Field Communication interface for Arduino built around the popular NXP PN532 integrated circuit.