The circuit uses a serial-in-parallel out shift register, 74HC595 for receiving serial data from uController board. See example of U5 in the schematic, SER is for data input, SRCLK is shift clock and RCLK is Latch clock. Each data bit is shifted into the register on rising edge of the shift clock. When all data bits are shifted into the 8-bit register, the rising edge of RCLK will clock the data to be latched at each output bit. [via]
SPI Interface Big 7-Segment LED - [Link]
ibsimed1 have developed a single I/O-Pin 3×7-Segment Display board. It only needs one microcontroller I/O pin and power source. The board itself is very simple but idea is great – it uses three serial to paralel converters 74HC164 which activates LED segments. As it is said – display board uses only one I/O pin which also serves as CLK source for serial to paralel converters (from 500kHz to 8MHz). [via]
Control 3×7 segment LED display with one MCU pin - [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 instructable will show you how to create a multifunction platform with a thermometer, chronograph (count up timer), count down timer, and light display. It is also intended to be a platform for other analog sensors or any other functions you can think of. Project is based on Atmega168 microcontroller. Information is displayed on dual 7 segment LED display.
Multifunction Digital Thermometer - [Link]
This project is a 3-digit digital thermometer easy to build for beginner or hobbyits.PIC16F628 used to read digital value
of temperature from a DS1820 sensor.All 7-segments drived by power logic 8-bit shift register TPIC6B595 with open collector output. For the 7-segment need 12V volt to drive because it have 3 LED per one segment.All segment no need to scan display. Source code programming with CCS C Compiler availible.
2.3 ” Digital thermometer - [Link]