AmebaMotors – Control motorcars with Ameba

Wiring:

Note:

• We connect Ameba 5V to L298N +12V to supply power. However, not every L298N accepts 5V power supply, if this does not work, please connect L298N +12V to other power supply (e.g., +12V) and use L298N +5V to supply power to Ameba.
• The correct wiring of the motor depend on each model (may be opposite). Please run the test program first, make sure it runs correctly before assembling the motorcar.
• For convenience purposes, it’s recommended to use dupont line to organize the wiring of motors and L298N.

Everytime you modify your program, please remember to unplug the power of L298N to avoid the motor running unexpectedly. Connect Ameba to power, upload the program, and then connect L298N to power when you are going to test the proram.

Compile and upload the “car2wd_digital_control” example to Ameba.
In this program, we make the motorcar to perform following moves:
Move forward 2s => Stop 1s => Move backward 2s => Stop 1s => Rotate in clockwise direction 2s => Stop 1s => Rotate in counterclockwise direction 2s => Stop 1s => Move forward and turn right then turn left => Stop 1s => Move forward and turn left then turn right => Stop 1s => ……

Next we describe the control of the motorcar in the following:

• Speed: We control ENA and ENB via PWM, frequency is fixed at 200 (resolution=256).
• Move Forward：
  

  IN1	IN2	IN3	IN4
  HIGH	LOW	HIGH	LOW

• Move Backward:
  

  IN1	IN2	IN3	IN4
  LOW	HIGH	LOW	HIGH

• Clockwise Rotation: Control the left-side motor to move forward, and right-side motor to move backward:
  

  IN1	IN2	IN3	IN4
  HIGH	LOW	LOW	HIGH

• Counterclockwise Rotation: Control the right-side motor to move forward, and left-side motor to move backward:
  

  IN1	IN2	IN3	IN4
  LOW	HIGH	HIGH	LOW

• Move forward and turn right: There are two ways to perform this movement.
  • First, let the motors on left-side and the motors on right-side to rotate in different speed. However, considering the quality of the wheels of motorcar set, this approach may not work as we expect.
  • Second, we let the motors on one side to run and stop in turn. This approach works on most models of motorcars.
    Firsr, set the motor to move forward:

    IN1	IN2	IN3	IN4
    HIGH	LOW	HIGH	LOW

    Then we set the IN3 pin to LOW for 80ms, then HIGH for 20ms, then LOW for 80ms, and so on.
    Move forward and turn left, move backward and turn left/right are also done in a similar way.

If the program functions correctly, you can assemble the motorcar.
Below is the demo video of this example:

• Control GPIO in register level
  Since we need to control the motor in real-time, we need to control GPIO in register level. (High-level API provided by Arduino, e.g., digitalWrite(), requires long reaction time. )
  1. First, GPIO setting: pinMode(in3, OUTPUT);
  2. Next, keep the port and the bit mask of this GPIO pin in mind. Usually the input, ouput or other control bit of GPIO would be in the same register. The port stands for the corresponding register of the GPIO we want to control. The bit mask is used to identify the bit we want to control.
     

     in3_port = digitalPinToPort(in3);  // Get the port of in3
     in3_bitmask = digitalPinToBitMask(in3);  // Get the bit mask of in3
     

  3. Controlling GPIO
     

     // Set the output port of in3 to 1, now in3 is HIGH
     *portOutputRegister(in3_port) |=  in3_bitmask;
     // Set the output port of in3 to 0, now in3 is LOW
     *portOutputRegister(in3_port) &= ~in3_bitmask;