I do not have a series resistor in my circuit. Is that a standard value per LED?
How are you physically connecting the shield and the led at the same time?
Take a look at the photo. This is a variant with a double row of connector holes.
How are you physically connecting the shield and the led at the same time?You can use Ohm's law to calculate the series resistors for LEDs. To do that you need to know the forward voltage of the led and the current you want to flow. The current, of course, must not exceed the max current the led is specified for, or the max current that can be provided by the driver, in your case the 2 Arduino pins. You don't have to use the highest possible current, you can choose a lower current to dim the led.Ohm's law says R=V/I where V is the voltage across the series resistor and I is the current flowing through it. The voltage between the two pins is, in theory, 5V. Let's say your led has a forward voltage of 1.5V. So the voltage across the resistor will be 5-1.5=3.5V. If you want 25mA to flow, the resistor should be = (5-1.5)/0.025=140R. You then need to pick the closest standard resistor value that is above that, eg 150R.If you put 2 LEDs in series (not in parallel as shown in the schematic you posted earlier), their forward voltage add together. Let's say that's 2x1.5=3.0V. So your series resistor can be (5-3.0)/0.025=66R. Nearest standard value is 68R.