A4988 Stepper Driver: Current Limit and First Steps

Before you start

Board and software

Classic ESP32-WROOM-32/32E DevKit with the listed GPIOs exposed and unused. Arduino IDE 2.x; esp32 by Espressif Systems 3.3.2 (review baseline, not a latest-release claim). Select the documented board or ESP32 Dev Module for a generic WROOM board. Other families need their own pin map. Serial Monitor: 115200 baud.

Supported hardware

Worked carrier: Pololu A4988 item 1182 with published schematic/labels, not unidentified purple artwork. Four-wire bipolar motor with documented coil pairs and rated phase current at least 0.5 A. Set driver limit ≤0.5 A and ≤motor rating. No universal size or step angle assumed.

Prerequisites and parts

Complete Blink and board pin checks. Reference carrier, documented motor, current-limited regulated 12 V supply sized for actual load, ≥47 µF / ≥25 V capacitor near VMOT, meter, short suitable power wiring and 10 kOhm resistors. Set VREF first. Keep motor power paths off ordinary breadboard rails.

Libraries

Arduino-ESP32 3.3.2 GPIO and delay only; no extra library.

Expected result

After command g, 100 full-step pulses in one direction, then outputs disabled. Angle depends on actual motor; software count does not prove motion.

Verification status

Documentation and source review only. Not compiled or tested on hardware. The approved product-style illustration identifies a family, not a verified physical pin layout or manufacturer-authenticated board. Follow the logical diagram and documentation for your actual part.

Overview

02Technical Specifications

Arduino library: Arduino-ESP32 3.3.2 built-in GPIO and timing; no extra library.

03Pinout

• VDD Logic ESP32 3V3 Reference VDD, not VMOT.
• Logic and motor GND Reference ESP32 GND / supply negative Motor return directly to supply, not GPIO wiring.
• VMOT Power External regulated +12 V Never connect to ESP32.
• ≥47 µF / ≥25 V capacitor Bulk + VMOT; − motor GND Close to carrier; not a guarantee against all spikes.
• STEP Pulses GPIO25 + 10 kOhm to GND Hardware pull-down.
• DIR Direction GPIO26 + 10 kOhm to GND LOW for the example.
• /ENABLE Enable GPIO27 + 10 kOhm to 3V3 Active LOW; reset pull-up disables outputs.
• /RESET and /SLEEP Run Both joined to VDD (3.3 V) Actual pin labels, not artwork geometry.
• MS1, MS2, MS3 Full step GND All selection inputs LOW.
• 1A / 1B Winding Motor coil A pair Identify continuity with all power removed.
• 2A / 2B Winding Motor coil B pair Never connect while powered.

04Wiring Diagram

VDD3.3 V; VMOT12 V with local capacitor; common GND. STEP25, DIR26, /ENABLE27. RESET/SLEEP HIGH, MS1–3 LOW; separate winding pairs to 1A/B and 2A/B.

Open wiring diagram at full size (new tab)

1. 1

   Unpowered, identify carrier labels, Rs and motor coil pairs. Use manufacturer VREF procedure to set Imax ≤0.5 A and ≤motor rating. Rs=0.068 ohm gives 0.272 V for 0.5 A; do not copy to another Rs.

2. 2

   Adjust VREF with the motor disconnected using the manufacturer procedure, avoiding shorts/unintended outputs. Full-step coil current is about 70% of Imax; supply current is not a substitute. Remove power before attaching motor.

3. 3

   Install capacitor near VMOT, wire grounds/supplies/control pull resistors. Upload with motor power off. Keep shaft clear and unloaded.

4. 4

   Power the documented setup, send g at 115200 baud. The bounded pulse burst finishes disabled. Disconnect both supplies before wiring changes.

Wiring and matching Arduino code

Commanded full-step pulse burst

VDD3.3 V; VMOT12 V with local capacitor; common GND. STEP25, DIR26, /ENABLE27. RESET/SLEEP HIGH, MS1–3 LOW; separate winding pairs to 1A/B and 2A/B.

#include <Arduino.h>
constexpr uint8_t STEP_PIN = 25;
constexpr uint8_t DIR_PIN = 26;
constexpr uint8_t ENABLE_PIN = 27; // active LOW
void setup() {
  Serial.begin(115200);
  pinMode(ENABLE_PIN, OUTPUT);
  digitalWrite(ENABLE_PIN, HIGH);
  pinMode(STEP_PIN, OUTPUT);
  pinMode(DIR_PIN, OUTPUT);
  digitalWrite(STEP_PIN, LOW);
  digitalWrite(DIR_PIN, LOW);
  Serial.println("Set current limit first. Send g for 100 full-step pulses.");
}
void loop() {
  if (Serial.available() == 0) return;
  if (Serial.read() != 'g') return;
  digitalWrite(ENABLE_PIN, LOW);
  delay(2);
  for (uint16_t n = 0; n < 100; ++n) {
    digitalWrite(STEP_PIN, HIGH);
    delayMicroseconds(5);
    digitalWrite(STEP_PIN, LOW);
    delay(10);
  }
  digitalWrite(ENABLE_PIN, HIGH);
  Serial.println("100 pulses sent; outputs disabled. Movement is not sensed.");
}

Hardware /ENABLE pull-up provides reset bias. About one-second burst intentionally blocks other work: first bench test, not motion-control scheduler. Disabled motor has no holding torque; no gravity-loaded axis. Current limit is hardware setup, not code.

How it works

Technical references

• Pololu A4988 carrier 1182 — Worked carrier labels, power, current limiting and thermal guidance.
• Allegro A4988 — STEP timing, current-limit equation and mode/logic requirements.
• Arduino-ESP32 3.3.2 GPIO — Pinned GPIO output implementation.