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7-Segment Display

A classic single-digit LED indicator used to display numerals and basic characters in retro electronics.

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7-Segment

The 7-segment display is an arrangement of 7 distinct LEDs in a figure-8 pattern (plus a decimal point). By selectively turning on specific combinations of these segments, you can display any number from 0 to 9, as well as several alphabetical characters. It comes in Common Anode and Common Cathode variants.

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Overview

Before LCDs and OLEDs became ubiquitous, 7-segment displays were the primary way devices communicated numeric information to users. They are still widely used today due to their low cost, high visibility, and simplicity.

Pin Reference

Pin	Type	Description
A	digital	Controls the top horizontal segment.
B	digital	Controls the top-right vertical segment.
C	digital	Controls the bottom-right vertical segment.
D	digital	Controls the bottom horizontal segment.
E	digital	Controls the bottom-left vertical segment.
F	digital	Controls the top-left vertical segment.
G	digital	Controls the middle horizontal segment.
DP	digital	Controls the Decimal Point (dot) at the bottom right.
COM.1	power	Common pin (connects to VCC for Anode, GND for Cathode).
COM.2	power	Second Common pin (internally connected to COM.1).

Configurable Attributes

Attribute	Type	Default	Description
color	string	"red"	The color of the illuminated segments.
common	string	"cathode"	Sets the display type. Use "anode" or "cathode".
digits	number	1	Number of digits (if multi-digit component is used).
colon	boolean	false	Enables a colon (:) between digits, usually for clocks.

Working Principle

• Common Cathode: All 8 LEDs share a single Ground (COM). To turn a segment ON, you supply HIGH logic to its respective pin (A-G).
• Common Anode: All 8 LEDs share a single VCC (COM). To turn a segment ON, you supply LOW logic to its respective pin, allowing current to sink into the microcontroller.

Wiring Diagram

Example Arduino Code

To simplify wiring and logic, the SevSeg library is highly recommended.

#include "SevSeg.h"
SevSeg sevseg;

void setup() {
  byte numDigits = 1;
  byte digitPins[] = {10}; // Connect COM to pin 10 if multiplexing, otherwise ignore
  // Pins in order: A, B, C, D, E, F, G, DP
  byte segmentPins[] = {2, 3, 4, 5, 6, 7, 8, 9};
  bool resistorsOnSegments = true;
  
  // Initialize as Common Cathode
  sevseg.begin(COMMON_CATHODE, numDigits, digitPins, segmentPins, resistorsOnSegments);
  sevseg.setBrightness(90);
}

void loop() {
  // Display the number 4
  sevseg.setNumber(4);
  sevseg.refreshDisplay(); // Must run repeatedly if multiplexing
}

Simulation Notes

• The simulator models both common anode and common cathode behaviors based on the common attribute.
• Multi-digit displays use multiplexing, which requires rapid switching in the Arduino loop(). If the simulation stutters, the display may appear to flicker just as it would in real life if the refresh rate is too low.

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