⚙️ Speed Control with SoifGo

💡 Control two DC motors independently over Bluetooth using a TDA7073A motor driver and software PWM on Arduino Uno.

🔌 Compatible Motor Driver Chips (Dual DC Motor)

Chip	Max Current per Channel	Voltage Range	Notes
TDA7073A	600 mA	3V – 18V	The one used here; great for small motors
L293D	600 mA	4.5V – 36V	Very common but old; high voltage drop
SN754410	1A	4.5V – 36V	Improved L293 with thermal protection
TA7291P	1A (2A peak)	4.5V – 20V	Designed for DC motors; built-in flyback diodes
TB6612FNG	1.2A (3.2A peak)	15V max	Very efficient, low drop; modern L293D replacement
DRV8833	1.5A (2A peak)	2.7V – 10.8V	Battery-friendly; full protection features
MX1508	1.5A (2.5A peak)	1.8V – 10V	Very cheap; ideal for toys and small robots

📖 About the Speed Control Example

This Arduino sketch lets you control the speed of two DC motors independently over Bluetooth using a TDA7073A motor driver. It uses software PWM (no hardware PWM pins required) and communicates via the Arduino Uno's built-in hardware serial (pins 0 and 1).

⚠️ Important — Software PWM:
Unlike the typical analogWrite() approach, this sketch generates PWM in software inside loop(). This means:

Any output pin can be used (here: A2, A3, A4, A5).
The PWM frequency is low (~a few hundred Hz) and depends on loop speed.
Serial parsing is done in the same loop, so keep commands short.

How it works

setup() — Configures the four motor driver pins (M11, M12, M21, M22) as outputs, sets them LOW (motors stopped), and starts serial communication at 9600 baud.
loop() — Runs the software PWM for both motors and checks for incoming serial data.
Motor 1 (A): If stopm1 is false, spd1 increments each loop. While spd1 < pw1, the motor is driven in the direction set by dir1. When spd1 exceeds pw1, the motor is turned off for the rest of the cycle.
Motor 2 (B): Same logic using spd2, pw2, and dir2.
parseSerial() — Called when a newline is received. Parses the accumulated text string for commands.

Commands accepted

Command	Action
`FWD`	Motor 1 forward (`dir1 = true`)
`BACK`	Motor 1 backward (`dir1 = false`)
`LEFT`	Motor 2 left (`dir2 = true`)
`RIGHT`	Motor 2 right (`dir2 = false`)
`STOP`	Stop both motors (`stopm1 = true; stopm2 = true`)
`SPD_A:200`	Set Motor A speed (0–255) → `pw1`
`SPD_B:150`	Set Motor B speed (0–255) → `pw2`

📌 Note: After each valid command, the sketch prints the current speed values: pw1 pw2 (e.g. 55 55). This is useful for debugging but is not a formal acknowledgment.

📜 Full Arduino Sketch

/*
  SoifGo — Speed Control  for TDA7073A (Software PWM)
 
  Target: Arduino Uno R3 (ATmega328P)
*/

// ============================================
// PIN CONFIGURATIONS (same as Bascom)
// ============================================
const byte M11 = A2;  // PORTC.2
const byte M12 = A3;  // PORTC.3
const byte M21 = A4;  // PORTC.4
const byte M22 = A5;  // PORTC.5

// ============================================
// VARIABLES
// ============================================
bool dir1 = false;
bool dir2 = false;
bool stopm1 = true;
bool stopm2 = true;

byte spd1 = 0;
byte spd2 = 0;
byte pw1 = 55;
byte pw2 = 55;

String text = "";
String text2 = "";

// ============================================
// SETUP
// ============================================
void setup() {
  pinMode(M11, OUTPUT);
  pinMode(M12, OUTPUT);
  pinMode(M21, OUTPUT);
  pinMode(M22, OUTPUT);

  // All motors stopped initially
  digitalWrite(M11, LOW);
  digitalWrite(M12, LOW);
  digitalWrite(M21, LOW);
  digitalWrite(M22, LOW);

  Serial.begin(9600);
}

// ============================================
// SOFTWARE PWM LOOP
// ============================================
void loop() {
  // ---- Motor 1 (A) ----
  if (!stopm1) {
    spd1++;
    if (pw1 > spd1) {
      if (!dir1) {
        digitalWrite(M11, HIGH);
        digitalWrite(M12, LOW);
      } else {
        digitalWrite(M11, LOW);
        digitalWrite(M12, HIGH);
      }
    } else {
      digitalWrite(M11, LOW);
      digitalWrite(M12, LOW);
    }
  } else {
    digitalWrite(M11, LOW);
    digitalWrite(M12, LOW);
  }

  // ---- Motor 2 (B) ----
  if (!stopm2) {
    spd2++;
    if (pw2 > spd2) {
      if (!dir2) {
        digitalWrite(M21, HIGH);
        digitalWrite(M22, LOW);
      } else {
        digitalWrite(M21, LOW);
        digitalWrite(M22, HIGH);
      }
    } else {
      digitalWrite(M21, LOW);
      digitalWrite(M22, LOW);
    }
  } else {
    digitalWrite(M21, LOW);
    digitalWrite(M22, LOW);
  }

  // ---- Serial parse ----
  if (Serial.available()) {
    char c = Serial.read();
    if (c == '\r' || c == '\n') {
      if (text.length() > 1) {
        parseSerial();
      }
      text = "";
    } else {
      text += c;
    }
  }
}

// ============================================
// PARSE SERIAL
// ============================================
void parseSerial() {
  if (text.indexOf("FWD") >= 0) {
    dir1 = true;
    stopm1 = false;
  }
  if (text.indexOf("BACK") >= 0) {
    dir1 = false;
    stopm1 = false;
  }
  if (text.indexOf("LEFT") >= 0) {
    dir2 = true;
    stopm2 = false;
  }
  if (text.indexOf("RIGHT") >= 0) {
    dir2 = false;
    stopm2 = false;
  }
  if (text.indexOf("STOP") >= 0) {
    stopm1 = true;
    stopm2 = true;
  }
  if (text.indexOf("SPD_A:") >= 0) {
    text2 = text.substring(6, 9);
    pw1 = text2.toInt();
  }
  if (text.indexOf("SPD_B:") >= 0) {
    text2 = text.substring(6, 9);
    pw2 = text2.toInt();
  }

  Serial.print(pw1);
  Serial.print("   ");
  Serial.println(pw2);

  text = "";
  text2 = "";
}

📦 Download speed-control.ino

📝 Wiring notes for Arduino Uno R3

Bluetooth module (HC-05 / JDY-31): connects to the Arduino's hardware serial — module TX → Arduino RX (pin 0), module RX → Arduino TX (pin 1) (use a voltage divider if the module is 3.3V).
Motor driver pins: M11 = A2, M12 = A3 (Motor 1), M21 = A4, M22 = A5 (Motor 2).
For TDA7073A, each motor is driven by a pair of inputs (IN+ / IN-). Connect M11 → IN1+, M12 → IN1-, M21 → IN2+, M22 → IN2-.
Because the sketch uses hardware serial, disconnect the Bluetooth module while uploading the sketch to avoid conflicts.

🖼️ Schematic (Arduino Uno R3 Target)

Arduino Uno R3 + Bluetooth + TDA7073A Schematic

Arduino Uno R3 + Bluetooth + TDA7073A Wiring

🎬 Test Video

Speed Control test — two motors with independent speed (TDA7073A, software PWM)

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