How to Use A4988: Examples, Pinouts, and Specs

The A4988 is a microstepping driver designed for controlling bipolar stepper motors. It is widely used in applications requiring precise motor control, such as 3D printers, CNC machines, and robotics. The A4988 supports microstepping resolutions of full step, half step, quarter step, eighth step, and sixteenth step, enabling smooth and accurate motor operation. Additionally, it features adjustable current control, thermal shutdown, and overcurrent protection, making it a reliable choice for various projects.

• 3D printers for precise movement of print heads
• CNC machines for accurate tool positioning
• Robotics for controlling robotic arms and wheels
• Automated systems requiring stepper motor control

The A4988 is a compact and versatile stepper motor driver with the following key specifications:

The A4988 has 16 pins, each serving a specific function. Below is the pinout and description:

1. Power Supply: Connect VMOT and GND to the motor power supply (8V to 35V). Add a decoupling capacitor (e.g., 100 µF) across these pins to reduce voltage spikes.
2. Logic Voltage: Connect VDD and GND to the logic power supply (3.3V or 5V).
3. Motor Coils: Connect the stepper motor's two coils to the 1A, 1B, 2A, and 2B pins. Ensure the correct pairing of the motor wires.
4. Control Pins: Connect STEP and DIR to your microcontroller or control circuit. Use ENABLE, MS1, MS2, MS3, RESET, and SLEEP as needed for additional control.

1. Locate the small potentiometer on the A4988 board.
2. Use a multimeter to measure the voltage at the REF pin.
3. Adjust the potentiometer to set the desired current limit using the formula: [ I_{max} = \frac{V_{REF}}{8 \times R_{sense}} ] where ( R_{sense} ) is typically 0.1Ω (check your board's documentation).

Below is an example code to control a stepper motor using the A4988 and Arduino UNO:

// Define control pins
#define STEP_PIN 3  // Connect to STEP pin on A4988
#define DIR_PIN 4   // Connect to DIR pin on A4988

void setup() {
  pinMode(STEP_PIN, OUTPUT); // Set STEP pin as output
  pinMode(DIR_PIN, OUTPUT);  // Set DIR pin as output

  digitalWrite(DIR_PIN, HIGH); // Set initial direction (HIGH or LOW)
}

void loop() {
  // Generate a pulse to move the motor one step
  digitalWrite(STEP_PIN, HIGH); // Set STEP pin HIGH
  delayMicroseconds(1000);      // Wait for 1 ms
  digitalWrite(STEP_PIN, LOW);  // Set STEP pin LOW
  delayMicroseconds(1000);      // Wait for 1 ms
}

• Use a heatsink or active cooling if driving motors at high currents.
• Always power the logic voltage (VDD) before the motor voltage (VMOT) to avoid damage.
• Avoid connecting or disconnecting the motor while the driver is powered.

1. Motor Not Moving:

   • Check the wiring of the motor coils. Ensure the correct pairing of wires.
   • Verify that the STEP and DIR signals are being sent correctly.
   • Ensure the current limit is set appropriately for your motor.

2. Driver Overheating:

   • Use a heatsink or active cooling to dissipate heat.
   • Reduce the current limit using the potentiometer.

3. Motor Vibrates but Doesn't Rotate:

   • Check the microstepping settings (MS1, MS2, MS3).
   • Ensure the motor is receiving sufficient voltage and current.

4. FAULT Pin Active:

   • Check for overcurrent or thermal shutdown conditions.
   • Verify that the motor and power supply are within the driver's specifications.

Q: Can I use the A4988 with a unipolar stepper motor?
A: No, the A4988 is designed for bipolar stepper motors only.

Q: How do I select the microstepping mode?
A: Use the MS1, MS2, and MS3 pins to configure the microstepping mode as shown below:

Q: What happens if I exceed the current limit?
A: The A4988 has built-in overcurrent protection and will shut down to prevent damage. Reduce the current limit or improve cooling to resolve the issue.