Stepper motors divide a full rotation into a number of equal steps. They have multiple coils organized into groups called phases. By using electromagnets to energize each phase in sequence, the motor rotates one step at a time.

The stepper motor driver is the circuit that controls how the stepper motor operates. It works by sending current through the motor's various phases in pulses. The DRV8825, a microstepping driver, allows higher resolutions by enabling intermediate step locations, achieved by energizing the coils with intermediate current levels.

The serial port Bluetooth module is a fully qualified Bluetooth V2.0+EDR (Enhanced Data Rate) 3Mbps modulation module with a complete 2.4GHz radio transceiver and baseband. It uses a CSR BlueCore 04-External single-chip Bluetooth system with CMOS technology and Adaptive Frequency Hopping. In simple terms, the Bluetooth module manages the wireless communication channel — it can transmit and receive data wirelessly, communicating via serial communication, which makes it easy to interface with a microcontroller.

All the pixels on a TFT LCD screen are arranged in a row-and-column format, and each pixel is attached to a very tiny silicon transistor that rests directly on the glass panel. This setup allows each pixel to be given a charge, and for that charge to be maintained even when the screen refreshes to produce a new image.

#include "SPI.h"
#include "Adafruit_ILI9341.h"

These are the libraries needed for the project. The Adafruit_ILI9341 library controls the TFT LCD display, and since it depends on the Serial Peripheral Interface, the SPI library is also included.

#define dirPin 2
#define stepPin 3
#define stepsPerRevolution 200

#define TFT_DC 26
#define TFT_CS 24
#define TFT_RST 22
Adafruit_ILI9341 tft = Adafruit_ILI9341(TFT_CS, TFT_DC, TFT_RST);

This defines the direction and step pins for the stepper motor, as well as steps per revolution. Typical stepper motors move 1.8° per step, which works out to 200 steps per revolution. It also defines the DC, CS, and reset pins for the TFT LCD display and creates the TFT object with those pins assigned.

int input; //a string to hold incoming data
int lastInput;
int floorDiff;
int compensation;
bool stringComplete = false;

This initializes the variables used later. input stores the incoming data, and lastInput stores the previous input.

Serial2.begin(9600);
tft.begin();
displayFloor();
//Set pins as output
pinMode(stepPin, OUTPUT);
pinMode(dirPin, OUTPUT);

This sets the Serial2 baud rate to 9600 bps, the default for serial communication. The Arduino Due has 4 serial ports, and Serial2 is on pins 16 and 17. It also initializes the TFT display and immediately calls displayFloor(), then sets the stepper motor pins as outputs.

void moveUp() {
  digitalWrite(dirPin, HIGH);
  for (int i = 0; i < (1.8*stepsPerRevolution*floorDiff)+compensation ; i++) {
    digitalWrite(stepPin, HIGH);
    delayMicroseconds(1000);
    digitalWrite(stepPin, LOW);
    delayMicroseconds(1000);
  }
}

void moveDown() {
  digitalWrite(dirPin, LOW);
  for (int i = 0; i < (1.8*stepsPerRevolution*floorDiff)-compensation; i++) {
    digitalWrite(stepPin, HIGH);
    delayMicroseconds(1000);
    digitalWrite(stepPin, LOW);
    delayMicroseconds(1000);
  }
}

moveUp() and moveDown() are nearly identical, differing only in the direction pin — HIGH rotates the motor clockwise, LOW rotates it counter-clockwise. Each is a for-loop that steps the motor a set number of times, with delayMicroseconds() controlling speed. Steps per revolution is multiplied by floorDiff to determine how many rotations are needed, then adjusted by a compensation value. This compensation matters when using a one-sided rolling belt: as the belt rolls up, it accumulates radius and needs fewer rotations to reach the same height.

unsigned long displayFloor() {
  tft.fillScreen(ILI9341_BLACK);
  tft.setRotation(1);
  tft.setCursor(0, 70);
  tft.setTextColor(ILI9341_YELLOW); tft.setTextSize(2);
  tft.println("--===---===----===---===--");
  tft.setTextColor(ILI9341_WHITE); tft.setTextSize(5);
  tft.println("Mini Lift");
  tft.setTextColor(ILI9341_MAGENTA);  tft.setTextSize(3);
  tft.print("Current Floor:");
  tft.setTextColor(ILI9341_MAGENTA);  tft.setTextSize(3);
  tft.println(input);
  tft.setTextColor(ILI9341_YELLOW); tft.setTextSize(2);
  tft.println("--===---===----===---===--");
}

displayFloor() prints text on the TFT display. First the screen is filled black and rotated 90° for landscape view (the 1 in setRotation() means 90°, and can be set from 0–3). The cursor is then positioned so the text prints roughly centered on the screen — cursor coordinates of 0,0 would print at the top instead. Printing works like printing to the Serial Monitor, with the added ability to set text color and size.

displayMoving() is called while the stepper motor is moving, and shows which floor the lift is moving from and to. (char)24 and (char)25 render as up and down arrows, respectively.

void serialEvent() {
  while (Serial2.available()) {
    input = Serial2.read();
    displayMoving();
    stringComplete = true;
  }
}

This checks for incoming data on the Bluetooth serial connection. While data is available, it's stored in input, and the stringComplete flag is set to true to indicate the data was received successfully.

serialEvent();
if (stringComplete) {
  Serial2.print(lastInput);
  if (lastInput < input) {
    floorDiff = input - lastInput;
    moveUp();
  }
  else if (lastInput > input) {
    floorDiff = lastInput - input;
    moveDown();
  }
  displayFloor();
}
delay(100);
lastInput = input;
stringComplete = false;

The loop calls serialEvent() to check for new data. If data was received, it sends the last known floor back over Serial2, then compares lastInput and input to decide whether to call moveUp() or moveDown(), calculating floorDiff in the process. After moving, it calls displayFloor() to update the screen. The short delay gives communication time to process, and finally lastInput is updated and stringComplete is reset to false.

Connection Buttons

Floor Buttons

Stepper motors are really strong. A motor's position can be moved and held at any of its steps as long as it's carefully sized to the application in terms of torque and speed. In this build, it was able to lift a small platform of office supplies, and can lift heavier loads still, according to experiments conducted by other sources. Stepper motors like this one are used in a wide variety of applications, including industrial machines, medical scanners, blood analysis machinery, 3D printing equipment, and more.

• DRV8825 Stepper Motor Driver Carrier, High Current — Pololu
  (https://www.pololu.com/product/2133)
• All About Stepper Motors: What is a Stepper Motor? — Adafruit Learning System
  (https://learn.adafruit.com/all-about-stepper-motors/what-is-a-stepper-motor)
• Arduino TFT Display and Font Library — Instructables
  (https://www.instructables.com/id/Arduino-TFT-display-and-font-library/)

• Eddyson Canoy

• Lukie-Mar Lonzaga
• Miles Darren Bagnol
• Elijah Joseph Orias