Multiple problems.. somewhat frustrated

I am working on a project using an Arduino Duemilanove board. I just got all the parts and already have several issues.

First, the board does not turn on when I connect a power supply. I have a 12v wall wort, correct plug size, center ground (double-checked with multimeter). I plug it in, nothing happens. Isn’t this boar supposed to automatically select a powersupply?

Second, when I DO have it on (USB powered), it will not drive a servo. I tested the 5v and ground pins and they DO give 5v when connected to USB. I connected these to a servo. Originally I had my full code uploaded to the board, and the data pin on the servo connected to the pin I specified; nothing happened. I figured it was a code issue so I tried the provided example on Servo.h that makes a servo swing from 0 to 180 back and forth. With this code, nothing. I tested the data pin with a multimeter and it just looks like it is varying between ~100mV and ~500mV. Not sure if this is what PWM should look like on a slow (relatively) multimeter, but regarless it didn’t work.

Next I figured maybe the USB port can’t send enough juice to the servo. So I connected the + and - on the servo to a separate 6v power supply, and connected the data to the Arduino. Still diddly squat. Doesn’t even make a sound.

I guess it boils down to two main issues.

  1. The board will NOT turn on given a non-USB power supply.
  2. The Servo.h library is NOT controlling a servo, even enough to make it make a noise, for whatever reason.

Any thoughts? I REALLY want this to work, I put some money that I can’t really afford (broke college student) into this, I don’t want to scrap it because the controller I bought is junky. I don’t mean to offend anyone who holds Arduino dear, but I’m frustrated that nothing it is supposed to do, works. This is my first experience with this boards. Perhaps all of my problems are simply due to my own ignorance, in which case I stand corrected about these boards.

Sorry to rant (I tried to stay polite) and thanks in advance for any tips you can give me at this point!

center ground (double-checked with multimeter)

The center is the +ve not the ground, lucky for you there is a reverse polarity protection diode otherwise you might have blown it up.

So I connected the + and - on the servo to a separate 6v power supply, and connected the data to the Arduino. Still diddly squat. Doesn’t even make a sound.

Did you connect the - of the external power supply to the arduino ground?

Perhaps all of my problems are simply due to my own ignorance,

Looks like it but don’t worry we all had to start somewhere.

Sweet, ignorance on my part for the power supply issue. I had it in my head that the spec sheet said center ground for some reason, but it definitely says center positive. :blush: Tested it out, works as it should.

However, I tried the servo again with the power supply instead of the USB, and still nothing. The +5v and ground gives 5v on a meter as it should, and I connected the servo to those, and the data to pin 9 once again, and still nothing. The only thing I can think of is perhaps the fact that the only servos I have laying around are VERY old, and perhaps use a different style of PWM for data or take a lot more power or something? They work when not controlled by the Arduino (used them in other ways).

Anything to try to perhaps troubleshoot this? Maybe go buy a nice 2012 servo instead of ancient?

Are you trying to power the servo from the Arduino’s 5v pin?

Yes, is that not the way I should go about this?

USB only allows for 500mA. The on-board regulator doesn't have a hard limit. It is linear, which means the higher the input voltage the more power it dissipates itself. With 12V-in, you are severally current limited.

You probably need a separate 5V supply to power your servo. If you have a multimeter, measure the 5V while trying to pulse the servo. I think you'll find the supply is dropping below 5V (or at the very least fluctuating.)

So could I just buy a higher amperage wall wort and it should work?

Grumpy_Mike:

So I connected the + and - on the servo to a separate 6v power supply, and connected the data to the Arduino. Still diddly squat. Doesn't even make a sound.

Did you connect the - of the external power supply to the arduino ground?

Yes, I did, but I don't think the separate power supply had enough current to run the servo, apparently.

Yes it sounds like that to me as well. Have you tried them one at a time?