It's me again. This time I've got some crazy simple questions regarding my hardware components, so I hope you refrain from tittering as you answer me. Bear with me; I'm curing my ignorance little by little.
So first off, I have a LilyPad Arduino
that I bought from SparkFun, along with some yellow LEDs
As you can see, the LEDs have 2.0 to 2.4V DC forward drop, the max current is 20mA, and the suggested using current is 16-18mA.
The LilyPad has the following specs:
Operating Voltage 2.7-5.5 V
Input Voltage 2.7-5.5 V
Digital I/O Pins 14 (of which 6 provide PWM output)
Analog Input Pins 6
DC Current per I/O Pin 40 mA
In order to get enough voltage for the microcontroller, I'll use two AAA (1.5V) batteries in series.
That being said, on to my questions.
1. I want to use this microcontroller to control the operation of seven of the yellow LEDs. If I attach each LED to a single I/O pin, I'm thinking that, through Ohm's law, the resistance I'll need per LED is the following (rounding up to the nearest Ohm):
Power Supply Voltage = (Current from Pin - Current needed for LED) (Resistance)
3.0 V = (0.04A - 0.017 A)(R)
3.0 V = (0.023A)(R)
131 Ohms = R
Is that even right? What about the voltage drop over my LEDs? Does that factor in somewhere too?
2. I bought an enclosed battery holder from Radio Shack that holds two AAA batteries. I was wondering if it would be safe to assume that the batteries are connected in series, and not in parallel. It probably says so on the package, but I'm away from home at the moment, so I can't check. They sell it on their website
3. Finally, am I even correct in figuring that two AAA 1.5V general purpose batteries are appropriate for this setup? I know next to nothing about hardware or circuits, so maybe I need something more specialized. I just want to make sure. :x
Thanks in advance for all your patience with me. I know I must get on your nerves when my questions are probably so rudimentary.