ELLO 1A is among the simplest computing systems, built from only 25 components, some of which optional. It is in fact so simple that a prototype can be easily built on a breadboard. The PIC32 microcontroller is a single chip in the heart of the computer. It handles everything in software – the video, the interfaces, sound, and executing the C interpreter. The reason I chose this particular model is, because at the time of the design it was the most powerful microcontroller on the market, coming in a through-hole package. It is still quite limited in comparison with other modern chips, but at the same time is a completely reasonable option for the main goals of the project.
I have intentionally designed the schematic in such absolutely minimalistic way so it can be easily understood by anyone.
As an additional note, the diode D1 is to provide voltage level protection on the monitor’s input. All monitors though, include their own protection on the input, so installing D1 on the board is optional.
Pursuing maximum simplicity and the limited number of input/output pins on the microcontroller come at the expense of solutions which are not exactly “by the book”, and may make some hardcore engineers feel uneasy. One of the great advantages of the PIC32 is its sturdiness and tolerance toward imperfect environments, which works great for the purpose of this project.