Using an external power source and plugging in usb power

[singhm29]

Hello all,

Im wondering if I keep the jumper for the motorshield on and have my arduino being debugged through its usb port will this cause any issues? I have read up about powering the motorsheild and arduino but just to confirm that im not overlooking anything (http://www.ladyada.net/make/mshield/use.html) Is it unsafe in some way? Will something explode? Thanks!

[adafruit_support_bill]

That should not cause any problems.

[singhm29]

So i went ahead and kept the jumper on while connecting the usb port and debugging and some strange things have happened. Previously my project had no issues moving a servo and stepper motor while just plugged in from the wallplug but now I decided to stop taking off that jumper every time I was debugging and just kept it on. What happens now is that when I move the servo once it works fine but when I press the same pushbutton to move it back to its closed position it flickers the LCD screen and resets the arduino...

The solution seems to be when I have both the usb port and wallplug plugged in it works fine...its as if the arduino mega is used to having that extra juice now and refuses to work with just the powerplug! WHHHY?

[singhm29]

After doing some more research I came onto these two possible problems that could be causing my issues.

A) It is best to use a seperate dedicated power supply (or battery) for the servo motor(s). They can cause the voltage to dip and also can cause spikes (noise) that may cause the microcontroller to reset or glitch.

B) Note that you may have problems with Arduino resets if the battery supply is not able to provide constant power, and it is not a suggested way of powering your motor project.
-the powerplug im using is pretty old and I have no idea what it was used for previously so maybe a new better quality plug would solve things?

I am running
-arduino mega 1280
-a hobby servo, TRAXXAS 2018
-an RTC, DS1307
-motorsheild
- a stepper motor with 700 mA current usage
-a graphic LCD, Graphic ST7565 LCD running off the 3.3V of the board

I really want to be using just a wallplug as I am demoing this on monday and dont really want a usb cable coming out of it and a wallplug..would buying a wallplug with a higher current rating solve the issue? Im currently using one that is 12V, 2A output. Increasing the voltage beyond 12V is not recomenned from the Arduino Megas page...

[adafruit_support_bill]

With both a stepper and a servo, I would strongly recommend a separate supply (with jumper removed). Your existing 12v supply would be good for the stepper.

The servo ports on the motor shield use the 5v regulated supply from your Mega. Powering that with a 12v supply is making the regulator work extra hard. Something in the 7-9v range is ideal.

Servos can have pretty high current requirements on startup. Sometimes well over 1A. Try the above solutions. If you still have problems with the arduino resetting, you can wire the servos for a separate supply as well.