Controlling 7-Segment LED Display (74HC595)

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This Module is part of the grouping: Controlling 7-Segment LED Display

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.

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NOTE: All information contained within this article is pure opinion. Although this article is intended to help people, it may contain faulty or misleading information. This article is not to be considered professional opinion or advice, and is in no way a replacement for reading all safety/instructional documentation. Always remember to protect yourself when handling/using hazardous materials, as well as test new techniques before using them on projects/work intended to be handed in or used.

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