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Contributors: Gella

## Calculating Power Needs: Current Draw

In addition to checking the operating voltage of the LilyPad boards in your project, you'll also want to take a look at the current your project will draw compared to the current your microcontroller or battery source can provide.

The current draw of your project depends on the total number of LilyPad boards you have chosen to use in your project and applies to both LilyPad Arduino-controlled circuits and e-sewing projects. If your power supply or battery does not provide the current your project needs, the circuit may start acting in strange or unpredictable ways.

As with voltage, you can check the datasheets of the individual LilyPad boards to estimate what your project will use.

For projects using a LilyPad Arduino, check how much current each individual I/O (input/output) sew tab can provide - the amount of LilyPad boards, such as LEDs, will be limited by this number. For most LilyPad Arduinos this is 40mA per I/O sew tab.

It's also better practice to round up and assume your circuit will need more current than to not provide enough current.

If your project uses components that require a lot of current, like motors or large amounts of LEDs, you may need to readjust your power supply choice or even use a separate supply for the LilyPad Arduino and the current-hungry boards.

As you gain experience working with LilyPad boards, it will be easy to estimate the amount of current your project requires by looking at the boards' datasheets and doing some math. You can also find out exactly how much current your project uses by measuring it with a digital multimeter or variable DC power supply that has a readout for current.

Let's explore an example of a frequently asked question about LilyPad projects: How many LEDs can I connect to a LilyTiny (or LilyTwinkle) board?

A typical LilyPad LED uses 20mA of current at full brightness. Multiply that by the number of LEDs you’re using, add 10mA for the LilyPad that’s running everything, and you’ll have an estimate of your average current draw.

Example:

A project with 10 LilyPad LEDs connected to a LilyTiny Board

20mA * 10 + 10mA = 210mA

For more detailed information on working with LilyPad LEDs, take a look at our Powering LilyPad LED Projects.