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7-Segment Display

Seven LED bars (a–g) that light up to form the digits 0–9.

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How it works

A 7-segment display is just seven LEDs arranged as a figure-8 (segments a–g), plus a decimal point. Light the right combination and you get a digit — e.g. b and c make a '1'.

Like any LED group it's common-cathode (shared leg to GND, drive segments HIGH) or common-anode (shared leg to +, drive LOW), and each segment needs a current-limiting resistor. For several digits, use a driver chip like the MAX7219 instead of many pins.

Pins

a–g
The seven segments — each to a pin through a resistor.
dp
Decimal point (optional).
Common
To GND (common-cathode) or +5V (common-anode).

Ratings

Type
Common-cathode or common-anode
Current
~20 mA per segment

Tips

  • Check common-cathode vs common-anode — it flips the wiring and code.
  • One resistor per segment is correct; many drive 4+ digits with a MAX7219.