Simple Bicolor LED too dim - Arduino Uno

I tried using the Search on this forum and also Google but didn't find an answer, so please bear with me and help me if you can.
I am trying to use a bunch of bicolor green/red LEDs controlled by digital pins 2-11. These LEDs have 3 pins and are LHG3392 from Jameco. The center pin appears to be a common cathode (negative), and the other are the anodes for Red and Green. These LEDs work fine when I connect them to the 3.3 V power rail thru 220 ohm, but they are very dim when controlled by Uno.

When I connect the anodes to the digital pins (either with a 220 ohm current limiter or just a straight wire) and run my program, i get a very, very dim light. I think the pins are supposed to be able to source 40 mA, but am seeing only around 100 microamps, even when only one LED is active. Voh is 1.71 V when the Red LED is on very dim. Voh is 1.82 for the green. If I disconnect the LEDs, i see an unloaded voltage of about 4.8V

The Uno appears to work with simple 2-pin Red LED, but a simple 2-pin Green LED is a little dimmer. What I can't get to work is illuminating this stupid bicolor LED.

Any ideas?

Change the multiplexing rate in your code just at the part where ....... Oh no code so no soloution.

Did you forget "pinMode (x, OUTPUT);" ?

"Did you forget "pinMode (x, OUTPUT);" ?

Yes. Rookie mistake. I assumed it was a hardware issue. Thank you for the help.


Pins default to INPUT, therefore high-impedance, which would make the LED dimmer if they're not declared as an OUTPUT.

What you are doing when writing to a digital input is switching the 30K pull up resistor on and off. Therefore it acts as a very week output.