Running a DC motor using SPI, bit operations, and arrays

Projects General Guidance
1

Greetings!

I am currently a first year student in Electronic Maintenance. We've been learning Arduino for a while and we just started talking about Serial Peripheral Interface. We also made our own H-Bridge in order to run motors. I've been messing around and finding out how to make a DC run slowly accelerate through SPI and arrays, as I've already managed to do it through conventional methods, using an L2938N motor driver. I made a first array for the motor speed comprised of just pure bits (0-16). Then I made a second array that maps the first array and stores the speed as a float.

This is the code :

#include <SPI.h>

byte velo_motor[] = {
  B00000000,
  B00000001,
  B00000010,
  B00000011,
  B00000100,
  B00000101,
  B00000110,
  B00000111,
  B00001000,
  B00001001,
  B00001010,
  B00001011,
  B00001100,
  B00001101,
  B00001110,
  B00001111,
};

const int IN1 = 3;
const int IN2 = 4; 
const int ENA = 5;
const int ESPERA = 6;
const int SS_PIN = 10;


void setup() {
  Serial.begin(9600);
  SPI.begin();

  pinMode(IN1, OUTPUT);
  pinMode(IN2, OUTPUT);
  pinMode(ENA, OUTPUT);
  pinMode(ESPERA, OUTPUT);

}

void loop() {

  float velo_motor2[16]; // Second array which stores the speed as a float
  digitalWrite(IN1, HIGH);
  digitalWrite(IN2, LOW);
  digitalWrite(ESPERA, HIGH);

  for (int i = 0; i < 16; i++) {
    velo_motor2[i] = map(velo_motor[i], 0, 255, 0, 4500);  // Map to range 0-255
    digitalWrite(ENA, map(velo_motor[i], 0, 255, 0, 4500));
    Serial.println(velo_motor2[i]); // Print each mapped value
    delay(800); // Wait for 400 milliseconds before printing the next value
  }
}

I hooked up the motor but it doesnt slowly accelerate despite the values being quite correct. Is there something I'm doing wrong? I am a complete beginner at this and am eager to learn, so any input would help. Thank you!

2

Welcome to the forum

        digitalWrite(ENA, map(velo_motor[i], 0, 255, 0, 4500));

digitalWrite() will write either HIGH or LOW to the ENA pin. Is that what the code is intended to do ?

1 Like
3

note also that map() won't give you a float, it will truncate to get an integral value.

4

Post a connection and wiring diagram of the project.

5

Hello,

I just edited the code and I instead of digitalWrite(), I made it analogWrite(), as I intended to slowly accelerate the motor through the ENA port (by writing 0-255 but with the bits I assigned to velo_motor[].

6

Oh ok then so declaring velo_motor2 as a float wont do anything regardless?

7

You can not simply control motor speed, it depends on many other parameters. For a smooth start you have to overcome sticking friction, then continue with lower energy, depending on the motor load. For real control you need rpm feedback and a PID controller.

8

You’ll get an int value in a float

9

Thank you for your reply, I was using an L2938N motor driver the first time, and it worked. The time I wanted to do the same but using SPI and converting bits from the motor array into integers

10

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