aux power jack problems

I have worked my way through design and build of my project using an Arduino and an Easydriver 4.3 stepper motor driver and it all works great except … when I disconnect the USB cable and power the Arduino with a wall wart (12vdc center pos verified) in the external power jack, the motor still tries to run but only completes about 1/4 of the steps and just twitches the rest.

The Easydriver v4.3 is powered with a 12v gel-cell battery and the Arduino with a wall wart. I tried tying the negatives together, I verified the power from the wall wart … 12.2vdc I tried a second verified wall wart with the same results. I also tried powering the external jack from a 12v battery with the same results.

When I power the Arduino directly through the 5v pin with a regulated power supply it works perfect. I am thinking there must be a problem with the built in voltage regulator on the Arduino.

I did notice that if I touch the Arduino or the Easydriver circuit boards with my fingers the motor performance improves (capacitance issue?).

Am I missing anything … any suggestions?
Thanks!

When I power the Arduino directly through the 5v pin with a regulated power supply it works perfect. I am thinking there must be a problem with the built in voltage regulator on the Arduino.

Can you power the Arduino with a 12V regulated power supply through the power jack or by tying into the VIN pin? Preferably the same 5V power supply you used with the 5V pin. If it doesn't work, I'd say the voltage regulator is a good suspect.

I did notice that if I touch the Arduino or the Easydriver circuit boards with my fingers the motor performance improves (capacitance issue?).

Touch where? Metal parts/pins or press on the components themselves? If it's the latter you may have some bad solder joints in manufacturing. If it's metal, then....uh....I don't know :) I'm not favoring the capacitance theory given that it works with a 5V regulated supply.

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If I touch it anywhere, metal parts, circuits, on either of the boards (Arduino or Easydriver), the motor will run better.

This sounds like you do not have a common signal ground between the motor, motor driver and arduino.

I do have the grounds/negatives tied together from the Arduino and the Easydriver. The stepper motor didn't have a ground wire ... I will try grounding it as well ...

So I just tried with the motor frame grounded as well and I get the same thing????

The other cause of "magic fingers" could be the fact that the arduino output pins have not been set to be outputs in the setup part of the sketch.

void setup() { Serial.begin(9600); Serial.println("Starting Incubator.");

pinMode(StepPin, OUTPUT); pinMode(MotorEnablePin, OUTPUT); pinMode(HomePin, INPUT); . . .

Well there is one good thing ... I have MAGIC fingers!

I am only using three pins in this sketch. Should I set all the pins in a specific mode?

I have MAGIC fingers!

You indeed do. As do many true electronic engineers.

Now you have to learn how to use them o little one, and you will feel the force of electrons bending to your will.