Arduino UNO + DRV8825: NEMA 17 Motor Control

A stepper motor can position a camera slider, XY stage, or lead screw by counting steps. An Arduino UNO cannot drive the motor coils directly: its pins provide control signals, while a DRV8825 switches and limits the coil current. This guide uses an external 12 V supply, a four-wire NEMA 17 motor, and the wiring shown below.

NEMA 17 specifies an approximately 42 × 42 mm mounting face, not an electrical rating. Check your motor's rated current per phase before setting the driver. A typical 1.8° motor takes 200 full steps per revolution.

Driver pins and wiring

The carrier accepts a motor supply at VMOT and GND; it does not need a separate logic-power (VDD) pin. STEP advances one full step or microstep on each rising edge, and DIR selects the direction. ENABLE is active low. Both RESET and SLEEP must be high for the driver to respond to pulses. MODE0–MODE2 select the microstep resolution. Clockwise and counterclockwise depend on the motor wiring and mounting orientation.

Arduino UNO / supply	DRV8825	Purpose
D2	DIR	Direction
D3	STEP	Step pulses
D4, D5, D6	MODE0, MODE1, MODE2	Microstepping
D8	ENABLE	Output enable
5 V	RESET and SLEEP	Keep the driver awake
GND	GND	Common signal ground
External 12 V + / −	VMOT / motor GND	Motor power
Motor winding A	A1, A2	First coil
Motor winding B	B1, B2	Second coil

Connect the Arduino, driver, and motor supply grounds. Identify each motor winding with a multimeter: the two leads of one winding show a low resistance; leads from different windings do not. Wire one pair to A1/A2 and the other to B1/B2. Wire colors vary by motor, so do not rely on the colors in the drawing. To reverse rotation, change DIR or swap the two leads of one winding while power is off.

Place an electrolytic capacitor of at least 47 µF across VMOT and motor GND, close to the carrier. For this 12 V example, a 100 µF / 25 V capacitor is suitable; observe its polarity. Long supply leads can produce voltage spikes. Never connect or disconnect the motor while the driver is powered.

Set the current limit

The DRV8825 regulates winding current independently of the 12 V supply voltage. Set its current limit before running the motor. The DRV8825 relationship is

For a carrier with , this becomes : a 1.2 A limit calls for approximately 0.6 V at VREF. Check the resistor value on your board; carriers with different sense resistors need different settings. The limit should not exceed the motor's rated phase current, and the small carrier may need cooling well below the chip's nominal maximum current. Start with a conservative setting, test at low speed, then check motor and driver temperatures. Supply current is not the same as winding current.

Select microstepping

MODE0	MODE1	MODE2	Resolution	Pulses per turn for a 1.8° motor
LOW	LOW	LOW	Full step	200
HIGH	LOW	LOW	1/2	400
LOW	HIGH	LOW	1/4	800
HIGH	HIGH	LOW	1/8	1,600
LOW	LOW	HIGH	1/16	3,200
HIGH	LOW	HIGH	1/32	6,400

The other two combinations with MODE2 high also select 1/32. The example sketch sets 1/16, so two revolutions require pulses. More microsteps improve command resolution; they do not increase the motor's torque or speed.

Test both directions

Upload this sketch after wiring the circuit and setting the current limit. It turns two revolutions in each direction, with a one-second pause. The 5 µs high pulse exceeds the DRV8825's 1.9 µs minimum; the full pulse period is approximately 1 ms.

const int DIR_PIN = 2;
const int STEP_PIN = 3;
const int MODE0_PIN = 4;
const int MODE1_PIN = 5;
const int MODE2_PIN = 6;
const int ENABLE_PIN = 8;

const long STEPS_PER_REV = 200;
const long MICROSTEPS = 16;

void rotate(long revolutions, bool direction) {
  digitalWrite(DIR_PIN, direction);
  delayMicroseconds(2);  // Set DIR before the first STEP edge.
  const long pulses = revolutions * STEPS_PER_REV * MICROSTEPS;
  for (long i = 0; i < pulses; ++i) {
    digitalWrite(STEP_PIN, HIGH);
    delayMicroseconds(5);
    digitalWrite(STEP_PIN, LOW);
    delayMicroseconds(995);
  }
}

void setup() {
  pinMode(DIR_PIN, OUTPUT);
  pinMode(STEP_PIN, OUTPUT);
  pinMode(MODE0_PIN, OUTPUT);
  pinMode(MODE1_PIN, OUTPUT);
  pinMode(MODE2_PIN, OUTPUT);
  pinMode(ENABLE_PIN, OUTPUT);

  digitalWrite(STEP_PIN, LOW);
  digitalWrite(MODE0_PIN, LOW);
  digitalWrite(MODE1_PIN, LOW);
  digitalWrite(MODE2_PIN, HIGH);  // 1/16 microstepping
  digitalWrite(ENABLE_PIN, LOW);  // Enable outputs
}

void loop() {
  rotate(2, HIGH);
  delay(1000);
  rotate(2, LOW);
  delay(1000);
}

At 1,000 pulses/s and 3,200 pulses/revolution, the ideal speed is 18.75 RPM. If the motor hums or loses steps at higher speeds, lower the starting pulse rate and add acceleration before increasing VREF. A loaded axis cannot necessarily start at its target speed. For manual control, connect forward and reverse buttons from D9 and D10 to GND, configure both pins as INPUT_PULLUP, and emit pulses only while one button is pressed. Add limit switches before moving a slider or lead screw near a mechanical stop. Keeping ENABLE low preserves holding torque during pauses; disabling it can let a vertical load fall.

Replacing an A4988

Both carriers use STEP/DIR control and a similar footprint, but check these differences before swapping them:

Check	A4988	DRV8825
Finest resolution	1/16 step	1/32 step
Maximum motor supply	35 V	45 V
Minimum STEP high and low time	1 µs each	1.9 µs each
Logic supply pin	VDD input	FAULT output on the corresponding pin

The same mode-pin settings that select 1/16 on an A4988 can select 1/32 on a DRV8825: a 3,200-pulse move could become half a turn instead of one turn. Recheck the board orientation, microstep mode, VREF, and pulse timing after a swap. Do not copy the A4988's VREF setting; its current-limit relationship differs.

For the first power-up, verify the coil pairs, ground connection, capacitor polarity, RESET/SLEEP levels, and current limit. Test at low speed in both directions, then add acceleration and controls for the intended mechanism.

References: TI DRV8825 datasheet · Pololu DRV8825 carrier guide