Our pals at Design News has a great card counter electronics project you can build (PDF has the step by step and source code) – “Take down the house with this gadget. William’s handheld controller provides the display of a monitored process deviation — but after hours it doubles as a card counter. (In either case, the algorithm is identical.) It works by adding or subtracting manually-entered “event” counts to a common 8-bit counter register. The value is subtracted from a predefined mean to generate the error or variation around the mean. This error “index” selects a display state sequence, continuously scheduled in an LED display.” – Link.
HOW TO – Make a card counter device