PAGE 029 OF 150 · COLOURS, SIZES & TYPES
Bi-Colour LEDs
Two chips in one package give two colours.
LED SYMBOLTriangle points from anode to cathode; the arrows show light leaving the part.
What bi-colour LEDs are
A bi-colour LED holds two chips of different colours in one package, often red and green.
Two kinds
- Two-lead: the chips are wired in opposite directions, so reversing polarity swaps the colour.
- Three-lead: each chip has its own anode with a shared cathode, or the reverse, and both can be lit together.
Colour mixing
Lighting a red and green pair together produces an orange or yellowish colour, though the exact shade depends on the relative brightness of each chip.
Use a resistor for each chip, and drive two-lead types with alternating polarity from a microcontroller.
REMEMBER
Colour is set by the semiconductor material, not by the plastic lens.Try it yourself
Sketch the circuit on paper first, calculate the values, then build it on a solderless breadboard using a low-voltage supply. Measure with a multimeter before you make anything permanent.
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