Arduino Uno - powering with an external source

Development Boards Arduino
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Hi all

Literally the first time I have posted on a message board, made sure to read all the intro instructions and it is a bit frustrating not to figure out this particular issue I have on my own - but here I am, and I’d like some help.

I bought the Arduino Starter kit and some LEDs and have been toying with a few projects. I had no trouble working with the USB as my main source of power until I wanted to power a 144 LED RGB addressable strip (the NeoPixel from Adafruit). To power this I followed Adafruit’s schematic from here: http://learn.adafruit.com/assets/1170. I used the recommended 5V 2Amp power supply listed here: http://learn.adafruit.com/digital-led-strip/powering.

Works great. No problems at all with any part of it. I was pretty excited and showed some people how easy it seemed (dangerous attitude I have found out).

I am new to the electrical part but have been programming off and on for a few years so I was pleased with this, however I wanted to make it entirely portable, no wall adapter and no USB to the computer so I bought this 4 AA battery holder: https://www.sparkfun.com/products/552, believing this would supply the power I needed. I also bought a multimeter to be able to tell voltage differences if something was not working as I had expected.

I connected the battery holder the same way I connected the external power supply (using the DC barrel jack adapter: https://www.sparkfun.com/products/10288) but the Arduino Uno’s board LED did not come on. I measured the voltage and it was at a relatively constant 5.3V. Keeping the battery holder on, I plugged the USB connection into the computer and everything worked just as it did before.

This made me think maybe the board was not receiving enough power, so I plugged a 9V battery in the same way as the battery holder and no dice. However, plugging the USB in while the 9V battery was connected and everything worked fine again. I tried the 9V battery and the 4 AA battery holder and that did not work, I tried plugging the 9V battery through a connector into the barrel jack on the Arduino board itself and that did not work, I tried 2 9V batteries through the DC barrel jack and that did not work and I tried the 5V adapter in the barrel jack of the Arduino board with the 9V battery plugged in through the DC barrel jack and that did not work. It seems to me that the Arduino prefers something from that USB connection however I do not know what that thing is.

It has got me pretty perplexed. The answer is probably staring at me in the face and I am too ignorant to know how to troubleshoot correctly, and that itself is frustrating but I don’t quite know what to do. So here is my first post to a board, to help me out. Hopefully it is something so simple that I slap my head and learn something.

Thanks all for your help and let me know if I can be more specific, take pictures of the set up, etc. Anything to help.

Thanks!

2

4 AA batteries is not going to power 144 LEDs. How is everything wired, please draw a schematic or wiring diagram. When everything is disconnected, does a battery power the Arduino?

Is this what you have? http://www.adafruit.com/products/1506

Furthermore, sounds like are connecting 5V to the DC jack and/or to the Vin pin. These pins are regulated lines for board. You have to supply ~7V to these pins for the regulator to start.

On the page you linked to for the standalone Arduino, this is stated:

For a standalone application (not USB connected to a computer), you can power the Arduino from the same regulated 5V supply as the LEDs — connect to the 5V pin on the Arduino, not Vin, and don’t use the DC jack on the Arduino.

Have you tried to connected the positive wire straight to the 5V pin? Don’t forget to connect the grounds between everything. Warning on the Arduino site for this situation:

5V.This pin outputs a regulated 5V from the regulator on the board. The board can be supplied with power either from the DC power jack (7 - 12V), the USB connector (5V), or the VIN pin of the board (7-12V). Supplying voltage via the 5V or 3.3V pins bypasses the regulator, and can damage your board. We don’t advise it.

From the product page:

Maximum 5V @ 60mA draw per LED (all LEDs on full brightness)

So if you are going to turn on all the LEDs, 60mA x 144 = 8.64A @ full brightness.

It’s going to get pretty pricey for you to make this portable…

Also listed on the product page, a better tutorial for powering Neopixels specifically. http://learn.adafruit.com/adafruit-neop … uide/power

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Here’s part of the Uno schematic, showing the power paths. The raw Vin comes in via the barrel jack, through a diode and then to multiple places, one of which is a 5v regulator to run the 5v ATmega328. Vin also goes to a comparator circuit and if Vin > threshold, then the USB 5v is shut off. If Vin < threshold then the USB 5v powers the system (assuming it’s there). You need a minimum of 6.5v @ Vin to make the 5v regulator run. Assuming you weren’t trying to run the Neopixels, the 9v battery should have powered the Uno (alone). If it didn’t then ;

  • check the polarity of your connector. IIRC the center is supposed to be +.

  • diode D1 may have blown (unlikely).

{click on to open}

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Thank you both! All it took was a little bit more understanding of what was going on to help me through what turned out to be a relatively easy solution (albeit one that is quite embarrassing to admit). So I had been thinking that the schematic that I had posted as my basis for externally powering the Arduino was good enough to work. However that schematic had some sort of switch for deciding external vs. usb power and (maybe) that had some reason for not using the 5V pin on the Arduino nor the barrel jack. The 5V wiring went from the lights directly to the external power source while the Arduino served as the ground directly for the lights and for the external power source. I added in another wire from the power source to the Arduino to see what would happen and it worked. But both of your posts got my brain thinking along a different path than I had been going down so I appreciate your insights and expertise in the matter. And again, embarrassing to admit this so I appreciate your patience!

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Don’t be embarrassed… The only way to learn is to be like ‘wtf is this all about’?

This thread also helped me figure out the same exact issue.