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By ncWaterBot
Hi everyone, I've searched around here (and elsewhere) and still can't figure out what's going on.

I have an Arduino driving the control signals to the pololu motor driver board. The signals are correct according to both Pololu's website and the VNH3SP30 datasheet. I'm driving the direction lines and PWM. I don't need current sensing, and the diagnostic pins seem to be taken care of with on-board pull-up resistors.

When connected and powered (motor power on, chip power on, control lines both pulled to ground, PWM off), the Pololu board seems fine, but when I change the PWM signal and the direction lines, the small ground trace (shown below) fries. Any ideas would be great. I am stumped with this one. Thanks!
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By esklar81

For us to help, you'll need to provide additional information, including:
  1. specifications for the motors,
  2. wiring diagram for your system, and
  3. specifications for your power supply.

Meanwhile, if you replace the blown trace with a jumper, how much current flows through it? I suggest testing that first with no motors attached, then with the motors.

Good Luck,
By ncWaterBot
Thanks, esklar81. I'll check the current through a bridge tomorrow.

-The power supply is an Agilent supply running at 12v and current limited to 1.5A.
-I am running the motor controller without a load. The output is instead connected to an o-scope.
-The Arduino is being powered over USB, and supplies 5v to the Pololu board as well as chip ground

Below is a wiring diagram. It's basic because I wanted to check the circuit before making it apart of a larger project.

EDIT: I can upload a screenshot of the signals when the board blew if that's useful. But I'll have to wait till tomorrow afternoon to do that.
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By tecoist
When you show Out A and Out B connected to the oscilloscope, is it possible that one of those connections is probe-ground? If so, might oscilloscope ground also be connected to any of the other grounds in the circuit? If so, the H bridge chip will cheerfully try to blow 12V through those connections and fry your ground trace. It is, after all, a bridge driver. I would suggest trying to probe Out A and Out B differentially if you aren't already doing that. Mind you, you may be way ahead of me on this one, but that's the first thing that comes to mind when I see the motor terminals connected to "O-Scope probe" in the singular.
By ncWaterBot
Thanks tecoist. You're absolutely right. As it turned out, the o-scope was acting as a huge grounding plane. In my attempt to be extra careful - test everything before attaching any motors, etc. - I shorted out two boards :P Oh well. Thanks for the sanity check! :)