Seven-Segment LEDs

[last update: 2020-09-15]
Still a work in progress...
go to: 7-segment, 4-digit module (bare), Adafruit 865
go to: Adafruit 877 - backpack driver
go to: 7-segment, 4-digit 0.56" module w/ backpack, Adafruit 878
go to: 7-segment, 4-digit 1.2" module w/ backpack
-----

• A 7-segment module is (in its simplest form) a single character display:
  
  
• Each segment is lit by an LED, and selecting which segments you activate allows you to display all numeric and about half of the alpha characters.
  In practice they are most often used to display just numeric characters and hex characters A - F.
• Single-character modules are typically wired up as common-cathode (or the reverse with common-anode), such that you'll have 7 anodes, one for each segment, plus a common cathode for a total of 8 control lines for each digit.
  You may have additional control lines for decimal points or colons.
  All together, this makes the modules consume a lot of I/O lines.
• To make it worse, in practice, 7-segment characters are typically bundled in 2 or 4-character modules. This makes it completely impractical to try to control each segment with a dedicated I/O line.

• To get around this problem, the 7-segment modules are connected to a "backpack" module, that does the multiplexing to control all the segments in all the digits, and the backpack is itself controlled with i2c protocol, which only requires 2 signal lines plus power and ground connections to your microcontroller.

eof