Power your arduino

When you prototype your project, you are powering your arduino with the USB power. Once you’re ready for some field test, say the arduino controls your room temperature, you no longer want to tether your arduino on your computer, rather you need to power it either with a battery or an AC adapter

1. AC adapter

Arduino starting from Duemilanove has an automatic voltage selection chip that will switch to AC adapter or USB as needed so there is no need for jumpers or else. The arduino should be powered by an AC adapter that outputs DC. Some adapters outputs AC so read the description adapter. The barrel should accept 2.1mm center pin on the arduino power jack. Lots of adapters can fit but fails to secure so you will have power losses when the adapter plug is slightly twisted or turned. The best way to buy an adapter is to test it out. Here are the required specs:

Input: 110VAC or your local power grid voltage

Output: suggest 9V to 12V although you can go as low as 7V or as high as maybe 16V. 9V and 12V are most commonly found

Current limit: at least 200mA but hopefully no more than 1000mA or 1A. Unless you’re driving motors or powering large bright LEDs, choose a smaller current limit so if you short something, the adapter gives you an additional layer to avoid damage. If you choose a current limit that is too small, then the voltage will drop when excessive current is drawn until the protection circuit in the adapter trips and turns it off.

Polarity: This is very important. It has to be center-positive. A symbol for center-positive adapter is a “c” and a dot at the center of the c, with a line leading to the opening of the “c” and a positive sign next to it, indicating the center is positive. Here is a picture from wiki: we need the left one.

Where to buy: the best place to shop for an adapter is a surplus store. You can try out any one of them if you want and you pay only $2 for one. Elsewhere it’s wasting money and postage. When shopping for an adapter, try to pick one that is light-weight. The heavier ones are old-fashion transformers while the lighter ones are newer and use switching technology that saves energy.

2. Battery

To conveniently power your arduino with a battery, you can use a rechargeable 9V battery with an adapter like the following one:

http://dipmicro.com/store/TEB-10003

You will need this clip:

http://dipmicro.com/store/BH9V

Once you get the battery and clip, feed the red to Vin on the bottom of arduino and black to one of the two ground  pins near Vin. I once soldered two male pins on the end of the wires so it’s better than two bare wires that could touch each other any time.

The 9V battery, especially a rechargeable one won’t last very long. You may want to power your project with Lithium batteries. I have no experience on this topic. Maybe I will add something once I learn about it.