When you're running out of digital output pins on your Arduino-based projects, there are many options available to solve the problem. One of these is the use of shift registers - which in some cases can offer a neat way of controlling one or more groups of eight digital outputs using only three digital pins on your board. One reason for doing this is to control groups of LEDs without much effort, and this has been demonstrated by M Atkinson with their binary clock project.
By using three shift registers, the clock can display the time using 24 LEDs, with each group of eight LEDs representing the hours, minutes and seconds in binary. The time is kept using a real-time clock IC and thus the clock itself can be quite accurate and transferred to a finished product if so desired. However it also makes a great and quick project you can build on a solderless breadboard, for example:
For complete instructions on how to make your own version, plus some other interesting tutorials - check out the multiwingspan blog. And for more, we're on twitter and Google+, so follow us for news and product updates as well.
The tutorial in the link uses 74HC595 shift registers, and instead of working with fragile DIP-package versions - consider our EXPAND: shift register module. Containing the 74HC595, nifty blue power LED and labelled pinouts, it's easier to use and physically stronger for constant prototyping. For more information and to order, visit the product page.