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AVR and 8051 drive 2-colour LEDs

Design Tip

Two-colour LEDs consist of two LED chips, usually red and green, encapsulated in one 2- or 3-wire case. Inside the 2-wire case two LED chips are connected in anti-parallel, so the LED colour gets determined by the current direction. In the 3-wire case two LEDs share a common wire for their cathodes, while the anodes are connected separately. The latter allows setting different currents through the diodes and producing not only a pure red or green light but also various colour blends.