Motor control circuit advice with L298N

Discussion in 'The Projects Forum' started by nezumij, Apr 7, 2012.

  1. nezumij

    Thread Starter New Member

    Apr 7, 2012
    Hi all,

    I'm looking at controlling 2 x DC Motors (FA-130's) using the L298N and an Ardunio Uno, and after reading numerous forum posts and data sheets I've concluded my understanding with the following schematic (see attached).

    I would like some clarification as to whether my understanding/circuit diagram is correct, and I also have a few questions around the circuit.

    Here are some additional details:
    - The motors are the small hobby DC type, operating Voltage is 1.5 - 3V (1.5V nominal) with a stall current of 2.2A. They are being used to drive a small Tamiya tank kit.
    - I have 2 power sources, 4.8V(Vs) to drive the motors (4xAA's - 1.2V NiMH) and 5V(Vss) regulated from the Arduino, I'm powering the Arduino itself with a 9V battery (PP3).
    - I've opted not to buy a motor shield for the Arduino as I would like to understand more of the electronics involved.

    And here are my questions:

    1) For R1 and R2 in the diagram, I'm not sure what resistance these should be. I'm simply taking the 0.5ohm rating from the L298N DataSheet, I understand that the rating here will depend on the draw from the circuit, but I have no idea what I'm using to calculate this.

    2) I haven't bothered putting in a voltage regulator on the 4.8V supply, my understanding is that the batteries could peak briefly to 6V, and the L298N will cause a 2.5V drop when the supply finally reaches the motors, so I figured I didn't really need one?

    3) Do I need to separate the 2 power supply grounds, and ground everything to the 'correct' supply or can I use a single ground rail and hook everything up to that?

    4) For the pull-down resistors on Ardunio it's seems common to use 1Kohm - 10Kohm, but I'm not sure of the exact science here, if I'm simply pulling logic to 0V could I not use something a lot smaller?

    Thanks in advance for any help!