Issues with dfRobot Motorshield and Arduino

Hey Guys,

I’ve been having a rough time getting my arduino uno, dfRobot 2A motor shield, ping sensor, and 2 6v motors to work properly.

I have the Uno powered off of 5xAA for 7.5v.
The motor shield is powered of off 4xAA for 6v.
ping sensor powered off of the arduino and plugged into D14/A0.

When turned off the motor shield, the ping sensor works and reads fine. When i turn the motor shield on the ping sensor goes crazy. I checked the Voltage on the 5v and it runs at 5.04v with the motor shield on and off.

I went a head and uploaded the basic program for just the motor shield and 2 motors. I noticed that when i turned it all on the ping sensor’s ACT light still it up even though I didn’t have it in the program. After unplugging the SIG line on the PING sensor the act light was still blinking making me thing that the motors are polluting the arduino’s 5v with pwm signal.

Has anyone else seen this or have an idea what I can do?


Rev1. It seems that when i plug the ping sensor into the 5v from the Arduino I start to get issues. It is now starting to make it so the motor wont spin unless the 5v from the sensor is unplugged. I can however touch the sensor 5v to an external 5v supply and it works great. So i guess the question is why is the ping sensor causing issues? The power reads 5v on the arduino pin if the motors are off or on.

Some more helpful information. When i put a tester on the Ping sensor data pin it goes between 15 and 30 mv. When i turn on the motor shield it jumps to 1.8 - 2.0 volts. Do you guys think I have a bad motor shield? Why is the voltage bleeding like this? Can I put something on the data pin to keep the voltage down?