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There are three main types of 4 digit seven segment displays to be found on the market: Bare displays without any driver. These come in a variety of colors and with either decimal points or clock-type display with a colon dividing two sets of two digits. 74HC595-based displays. Usually these displays have two daisy-chained 74HC595 shift registers and rely on the host controller to fill the serial registers and handle the multiplexing.