When multiple LED are combined, they can be used to display numeric and alphanumeric information. The most basic type of display is the 7-segment LED.
The number of digits displayable solely depends on the number of 7-segment LED that you combine.
Controllers
Each segment in each display represents a single LED. One 7-segment display therefore consists of at least seven individual LED. Some displays include an additional decimal point and/or a colon. A typical 4-digit breakout board is made of 30 individual LED.
Wiring and controlling these LED directly would require 31 wires and 30 GPIO pins which obviously does not make practical sense. Specialized controller IC are used instead to control the LED. Here are a few commonly used controllers:
Multiplexing
These controllers use two separate strategies to control a variable number of 7-segment displays:
- Direct LED Control: similar to a generic port extender, the controller comes with individual GPIOs that can each be turned on and off. Each GPIO provides a constant current to drive exactly one LED. Combined, the GPIO can control exactly one 7-segment LED.
- Multiplexing: in order to control more than one 7-segment display, the controller uses multiplexing: it switches between separate 7-segment displays in high frequency. The same GPIO ports control many different 7-segment displays, one at a time, in rapid succession. By switching between the displays fast enough, the human eye does not notice any flicker (however most 7-segment displays do flicker when recorded with a camera).
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(content created Mar 28, 2024)