Hello friends! Today we will design a custom component in Proteus ISIS. This is useful when you need to document a circuit but cannot find the exact module, connector, or device in your installed library. We will draw a simple four-pin symbol, define its connections, and save it so that it can be placed like other library parts. The original purpose of this tutorial is schematic presentation, and we will keep that approach. A clear custom symbol helps another person understand how your project is connected. We will also discuss the extra information required before the same part can be used for PCB layout or electrical simulation. Our example is a fictional device named Test Device with VCC, GND, OUTPUT, and SIGNAL connections. These names let us practise the workflow without claiming to r ...