Output Devices

Board Editor

KiCad Optimization: I discovered an option to pre-configure track widths, which saves significant time during design.

Predefined track configuration.

Design rules must set the minimum value among all defaults to avoid errors.

New Techniques Applied

Trace Widths: I configured 0.8 mm for signal lines (ESP32S3 and 3.3V) and 1.5 mm for power lines (12V and GND) to handle higher current loads and prevent overheating.

"Flip" Technique for Through-hole Components

To make soldering easier on a single-sided board, I placed the female pins (for drivers and MCU) on the back side. This allows the pins to pass through the board to be soldered comfortably on the copper side.

Pin layout after applying the flip technique.

Final Board Layout

Results

Power consumption

Power Control and Calibration: DRV8825

To control the NEMA 17 stepper motors (model 17HS4401), I used the DRV8825 driver[cite: 1]. One of the fundamental characteristics of this module is its ability to manage independent power supplies: a low-voltage logic signal for communication with the microcontroller and a high-power supply for motor movement[cite: 1].

Current Adjustment via Vref

To ensure optimal operation and avoid thermal damage, it is crucial to limit the current that the driver delivers to the motor[cite: 1]. The DRV8825 features a precision potentiometer (adjustable with a screwdriver) that regulates the reference voltage (V_ref)[cite: 1]:

• Clockwise: Reduces the amperage delivered[cite: 1].
• Counter-clockwise: Increases the amperage delivered[cite: 1].

Theoretical Calculation of Reference Voltage (Vref)

Based on the motor's datasheet, the maximum current is 1.7A[cite: 1]. However, to protect the driver and improve efficiency, it is recommended to work at a safety current (I_chop), usually calculated at 71% of the motor's total capacity[cite: 1].

We use the formula provided by the driver manufacturer[cite: 1]:

Where:

• R_sense: Is the value of the sensing resistor on the module (commonly 0.100 in standard models)[cite: 1].
• I_chop: Is 71% of the nominal current (1.7A × 0.71 = 1.207A)[cite: 1].

By knowing most values and solving for V_ref (which is the value we must measure with the multimeter on the potentiometer), we ensure the driver's longevity[cite: 1]. If the value is too low, it won't work; if it's too high, there is a risk of burning the driver or the motor[cite: 1].

Final V_ref value set to approximately 0.6V.

Importance of Calibration

Setting the V_ref to approximately 0.6V is vital for two reasons[cite: 1]:

Code Used

Breadboard Test (Two Drivers)

#include <AccelStepper.h>

#define STEP_PIN_1    D1
#define DIR_PIN_1     D0
#define ENABLE_PIN_1  D3
#define STEP_PIN_2    D8
#define DIR_PIN_2     D7
#define ENABLE_PIN_2  D6

#define FULL_STEPS_PER_REV 200
#define MICROSTEP          1

const long TEST_STEPS = FULL_STEPS_PER_REV * MICROSTEP;
const float MAX_SPEED  = 1000.0;
const float ACCEL      = 2000.0;
const float CONT_SPEED = 750.0;

AccelStepper stepper1(AccelStepper::DRIVER, STEP_PIN_1, DIR_PIN_1);
AccelStepper stepper2(AccelStepper::DRIVER, STEP_PIN_2, DIR_PIN_2);

bool continuousMode = false;

void enableDrivers(bool enable) {
  digitalWrite(ENABLE_PIN_1, enable ? LOW : HIGH);
  digitalWrite(ENABLE_PIN_2, enable ? LOW : HIGH);
}

void setup() {
  Serial.begin(115200);
  pinMode(ENABLE_PIN_1, OUTPUT);
  pinMode(ENABLE_PIN_2, OUTPUT);
  enableDrivers(true);
  stepper1.setMaxSpeed(MAX_SPEED);
  stepper1.setAcceleration(ACCEL);
  stepper2.setMaxSpeed(MAX_SPEED);
  stepper2.setAcceleration(ACCEL);
}

void loop() {
  if (Serial.available()) {
    char cmd = Serial.read();
    switch (cmd) {
      case '1': continuousMode = false; stepper1.moveTo(stepper1.currentPosition() + TEST_STEPS); stepper2.moveTo(stepper2.currentPosition() + TEST_STEPS); break;
      case '0': continuousMode = false; stepper1.stop(); stepper2.stop(); break;
    }
  }
  if (continuousMode) { stepper1.runSpeed(); stepper2.runSpeed(); }
  else { stepper1.run(); stepper2.run(); }
}

Files I used this week

These are the files I utilized for my assignments this week.