Microcontroller and Motor Controller using same Power Source

Discussion in 'The Projects Forum' started by kring123, Oct 5, 2011.

  1. kring123

    Thread Starter New Member

    Feb 6, 2010
    15
    0
    Hello,
    I was hoping someone could provide me some advice on using the same battery to power my microcontroller as well as motors.
    In the past I have used a 9V alkaline battery to power my microcontroller and used a separate 9.6V NIMH battery pack to power my motors. However, space is limited in my current project and I'd like to use just the NIMH battery pack if I can.
    My concern is that the microcontroller won't get the +5V it requires from an LM7805 voltage regulator. Will the following circuit act as a voltage divider and provide all voltage to the motors and none to the microcontroller? Or can I expect a consistent 5V no matter if the motors are running or not?

    +9.6V ---------------> LM7805 V. Regulator ------> Microcontroller (Expecting +5V)
    |
    |
    |
    |
    ------------------------------------> Motor Controller (Expecting +9.6V)

    Many thanks in advance!
     
  2. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    It won't necessarily act as a voltage divider, but the motor may cause so much noise at the battery that the microcontroller resets. You can add a diode in series with the wire going to the regulator, and a cap to ground after the diode to keep the regulator supplied during a large transient. Use a Schottky diode like a 1N5819; they have a very low forward voltage, but more importantly they have a very low reverse recovery time (they turn off quickly).

    "Ground loops" can be a big problem. They can easily cause your microcontroller to crash.
     
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  3. tracecom

    AAC Fanatic!

    Apr 16, 2010
    3,869
    1,393
    What type of motor controller is it? And what type of motor is it? I'm just curious because 9.6V is a little unusual.

    I have a stepper motor controller that I built that uses a similar setup, i.e., a 12V power supply to the motor and also feeding a 7805 to power the μC. It works fine, but I have plenty of capacitors around the 7805 and another one across the darlington driver IC.
     
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  4. kring123

    Thread Starter New Member

    Feb 6, 2010
    15
    0
    The motor controller is actually an L298 Dual H-Bridge with some schottky diodes on the output along with one 0.1uf cap per motor.

    The motors I'm using are are small ~75RPM 12V gearmotors.

    I'll try the schottky diodes before the regulator. I have one 10uf cap on each side of the regulator. Hopefully that will be enough.

    Thanks for the replies.
     
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