In my course entitled "Microcontrollers: an Introduction" I discussed the architecture of microcontrollers. I showed how the central processing unit fetches instructions (or a program) from memory and decomposes the instructions into components that the control unit and the arithmetic logic unit can use to perform the desired operation or function. Here I will discuss how to design a simple circuit incorporating a microcontroller with a small footprint, small pin count, and a small amount of internal memory (both program and data memory). I will give program examples using the C programming language. Microcontrollers are simply microprocessors that include program and data memory and peripherals such as general-purpose input/output ports, timers, serial communications controllers, analog-to-digital converter, etc.