Making LED displays is fun. There are a a few tools that get used all the time, from row-column scanning to LED driver chips to multplexers and shift registers. This tutorial discusses some of the more popular methods for controlling large amounts of LEDs from a microcontroller, including their various strengths and weaknesses, and how they work. For more on this subject see chapter 14 of “Physical Computing“, where Dan O’Sullivan and I discussed it in more depth. I’ll also include some notes on how to apply these ideas to controlling multiple motors or other high-current loads.
Most microcontroller modules have a limited number of outputs. Even if you use the analog inputs as digital I/O, there are only 19 pins on an Arduino, for example. That’s a fairly typical number for an 8-bit controller, and it seems not nearly enough if you want to control, say, 100 LEDs or more. There are a couple ways around this problem. Without adding any additional hardware, you can make a matrix of your LEDs and control them using row-column scanning. If you want discrete analog control over one output at a time, you can use a multiplexer. For digital control over multiple pins, you could use an addressable latch or a shift register. If you need pseudo-analog control over multiple pins, you could use a PWM driver. There are also several LED driver chips that are designed specifically to control groups of LEDS.