I'm trying to get a closed loop motor controller running using a Freescale PowerPC MPC5554 microcontroller and a brushless DC motor. The motor has 2 quadrature encoder outputs that I am reading with my microcontroller to determine speed and direction. The problem I am running into is that when I wire everything up, and with the evaluation board not connected to power, as soon as I turn on the bench power supply that powers the motor, the 5V power status LED on the eval board lights up dimly and I see 2 volts there. This only happens when the quadrature encoder B signal is hooked up to the microcontroller quadrature decoder input(eTPU).
I have a Bench power supply with 0-30V output, an evaluation board with a 12V DC power supply, and a brushless DC motor.
I have the bench power supply +/- hooked up to the motor power/ground. I have a motor enable signal going from a 5V post on the evaluation board to the enable input on the DC motor. I have a PWM output from the microcontroller going to the input on the DC motor. I have the 2 quadrature encoder signals from the motor connected to 2 decoder inputs on the microcontroller.
The bench power supply has a GND output too. Do I need to connect this to anything? I tried connecting the "-" output of the power supply to the GND pin on the bench power supply and then connecting the GND on the bench power supply to a GND pin on the evaluation board. The current leakage still occurred regardless of whether or not I connected the GND from the bench supply to the evaluation board. How should I be using the GND pin on the bench supply and should I be common grounding the bench supply and the evaluation board the way I was doing above?
Can someone please help me understand what might be wrong here with my wiring? I know this is a bit lengthy, but feel free to ask for clarifications. I am clearly NOT a hardware guy.