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### Topic: LilyPad how many LEDs per petal? (Read 8873 times)previous topic - next topic

#### kommi10

##### May 07, 2014, 06:08 pm
(moved this post from the Projects section)

Hi all, newbie here trying to figure out how many LEDs I can run off a lilyPad petal for a small project.

If one LilyPad Micro LED takes 20mA of current, but one petal outputs 40mA, then how does Leah Buechley manage to string 7 LEDs onto one petal in her tutorial?

According to her design, you can string 7 LEDs onto one petal: http://www.flickr.com/photos/leahbuechley/2596552004

But according to the specs on of the LilyPad Main Board the DC current per I/O Pin is only 40 mA

Assuming that each LED will consume around 20mA of current, how is it possible to string 7 of them together onto one petal?

Unless each LED is eating way less than the 20mA's?

Also, not sure how I would use Ohm's Law to calculate anything here. I know the current (I) as 40mA, and I know the resistance of the thread as 28 ohms per  foot (lets say 2 feet are used, so 56 ohms).  So I can use Ohm's Law to calc the volatge needed as 2.24 volts. But not sure how that helps me? I plan on using a 3V 250mAh coincell battery to power the lilyPad itself.

#1
##### May 07, 2014, 07:29 pm
The LEDs are all in parallel.
The LEDs have a voltage drop, say 2V for Red since you using a 3V supply: