Introduction

This is the first kit in the "Hardware Basics" series. In it we will build a character generator — read-only memory that holds a font. You set a code from 0 to 15 with the switches, and a character lights up on the 5 × 7 screen: a digit or an icon.

The kit stands on its own: it starts from the transistor and takes nothing from other kits. Inside:

• transistors and resistors — the resistor is a new part here, a "weak wire", and it is what makes a ROM so simple;
• gates NOT and AND — we build them in the very first lesson;
• a decoder — it turns a code into "one lit row out of sixteen";
• a matrix — 16 rows × 35 columns, with a transistor wherever a character has a lit point.

455 transistors and 35 resistors in total.

What you will build

Five lessons: a ROM point → a decoder → characters 0–7 by hand → characters 8–F → your own character. At the end you have a ROM with a font that you can see with your own eyes: the pattern of transistors in the matrix is the letters themselves.