16×24 LED Matrix – Easy to use, chainable displays. These LED panels take care of all the work of making a big matrix display. Each panel has six 8×8 red matrix modules, for a 16×24 matrix. The panel has a HT1632C chip on the back with does all the multiplexing work for you and has a 3-pin SPI-like serial interface to talk to it and set LEDs on or off. There’s a few extras as well, such as being able to change the brightness of the entire display, or blink the entire display at 1 Hz.
16×24 LED Matrix – Easy to use, chainable displays - [Link]
Multiplexing is the most common technique for interfacing multiple seven segment LED displays to microcontrollers. Read this experimental tutorial to find out how this technique works.
Multiplexing Seven Segment LED Displays – [Link]
Josh at imsolidstate.com build a 9 digit pulse counter based on MC14453 3-digit BCD counter from ON semiconductor. A pulse counter is a circuit that counts the number of pulses arriving at the input of the circuit. Results are displayed on 7-segment displays. Many of these chips can be connected together to build a counter with as much digits as you like. Read circuit description on the link below. [via]
Build a 9-digit Pulse Counter - [Link]
This instructable describes how to charlieplex a bunch of 7-segment led displays.
Charlieplexing of discrete leds has been the topic of a few other instructables. The Charlieplexing LEDs- The theory and the How to drive a lot of LEDs from a few microcontroller pins comes to mind. They are both excellent and should be read by anyone that wants to gain a deeper knowledge of how charlieplexing really works.
Charlieplexing 7-segment displays is more or less the same as doing it with discrete leds, but with some changes to handle the fact that all the led segments have a common pin instead of being separate, and the need for buffering of the common output so the poor microcontroller can cope with the load.
Charlieplexing 7 segment displays - [Link]
This is very simple countdown timer implemented on 89C2051 microcontroller. One button is used to set time up to 99 seconds, another is for starting timer. Time is displayed on two 7 segment LED displays. Buttons and display scanning share same pins so algorithm has to check buttons and display time on LED displays in a row sequence. Source code is included that allows to modify program and compile.
Very simple countdown timer with 7 segment displays - [Link]