Nice, for my application i have a atmega328 with only A3-5 left and i need it to communicate with something else that can toggle 14 outputs(28 leds) -- 1 output can toggle 2 leds since they are 14 R/G leds.
If you want to connect 28 LEDs to an Arduino, you'd be much better off multiplexing them. The attached diagram shows 2 x 3 multiplexing, which you could expand to 4 x 7. C1 - C2 and R1 - R3 are Arduino pins (you'll need 11 pins for 28 LEDs). Choose the value of resistor R to get the peak current you want in each LED (20 to 25mA is probably about right).The diagram on the right shows how I was suggesting to connect 2 LEDs to one pin. However, if they are red LEDs, then a single 1n4148 in series may not be enough.[sorry, can't post the pics because of "uploader full" messages]
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