Controlling 7-Segment LED Display (74HC595)

In order to efficiently run a 7-Segment Red LED off of a microcontroller, it should be coupled with a 8-bit shift register such as the 74HC595. This permits communication to occur with just 3 pins as well as multiple register/display pairs to be daisy chained together using no additional microcontroller pins. The 8 outputs of the shift register can be linked to the display's pins in order to control all seven segments and the decimal point.

In order to use the display effectively with the provided example code, hook up the display's pins A - H to the shift register's outputs QA - QH respectively using resistors no smaller than 250 ohms (assuming a +5V power supply; we want to make sure current is 20 mA or below). Use larger resistors for a dimmer display. The (+) pins should be connected to the positive power supply. Because the positive power supply is wired to the display, segments are activated by connecting their pins to ground. The register will output LOW to pins that are to be turned on.

The OE and SRCLR pins are tied off to prevent the need for additional microcontroller pins at the cost of an unpredictable display during boot-up before the first commands are sent. The SER, RCLK, and SRCLK pins will be controlled by the microcontroller to achieve the desired display.

Single 7-Segment Display