Arduino Uno on AA batteries


I'm working on a really simple project teaching kids to code with the Arduino Uno (gotta be better than learning Office, right?!). They've built a basic fade app and would like to make a "magic egg" - a blown egg over an LED to diffuse the light, and a hidden battery pack in a "nest" of paper.

Should be easy, I said. (first mistake!)

However, I've bought a 6 x AA batteries holder (which can make 7.2 V rechargeable battery pack from NiMH / NiCd cells or 9V battery pack from alkaline cells, apparently),filled it with duracell AA's and plugged it in to the power jack (which steps down the power, right?) - no LED light. It doesn't fry the LED, just doesn't go.

Having replaced the batteries a few times, can I conclude that the cheapy ebay adaptor (second mistake!) here - doesn't work, or is there a step I'm missing?

Many thanks for your help,

That should work fine...

I'd guess the connector might be wired backwards. Typically the inside of the barrel-connector is positive (and that's what's needed for the Arduino), but there's no solid-rule and power supplies come both ways.

Do you have a multimeter? ...Probably a good thing to have in your teaching-situation. You can buy one online for around $20 USD.

You can also make a little tester with an LED & resistor. (The LED won't come-on if it's connected backwards, and you can compare the polarity of the battery with your regular power supply.) I have a little tester I made with a probe (something like [u]this[/u]), a couple of different-color LEDs (one for each direction) and an alligator clip. But for a quick-and-dirty tester for your battery power-supply, you can just solder a resistor & LED in series.

Or you might simply have a bad solder connection, or the barrel-connector might be the wrong size. (If it's the wrong size it would probably work when you wiggle it around.)