Motor Driver 18v15 Malfunctions when DIR set Low

I am trying to use the High-Power Motor Driver 18v15 (P/N 755) for a project, and I am seeing some strange results when DIR is set Low. The ugly block of PWM-like switching is the result of constant signals on the PWMH and DIR pins highlighted in red.

The driver is being controlled by an Arduino. We have a 10 V power supply providing power and a 10 Ω dummy load on the output. The Reset pin is held high to V+ through a 20 kΩ resistor. We tried giving PWMH a 50% duty cycle PWM signal and observed similar bizarre results whenever DIR was set low. We felt this screenshot was most illustrative of our dilemma. The scope should be reading 5.0V/division, but we do not have the 10x attenuating probe hooked up to it right now.

Our loop runs 1 second each of the following constant states:
PWMH = Low / DIR = Low
PWMH = Low / DIR = High
PWMH = High / DIR = Low
PWMH = High / DIR = High

Please let us know if we are missing something! Thanks for your help.


How do you have the oscilloscope probe connected to the circuit? From your screen capture, I suspect that you might have the probe connected across the load, where the ground wire of the probe is actually connected to one of the motor outputs. If this is the case, there could be many things going wrong (you could potentially have a lot of current going through your oscilloscope).

Could you tell me more about your setup? Could you post pictures showing all the connections? Could you also post the code you are running on the Arduino?

- Jeremy