Weekly Assignments Final Project About me

Week 10 Output Devices

Objectives

  • Group assignment:Measure the power consumption of an output device
  • Individual assignment: Add an output device to a microcontroller board you've designed, and program it to do something.

    • Group Assignment

    In this week's assignment, I learned how to measure the power consumption of an output device using a bench power supply. We tested an MG90S servo motor connected to a custom PCB by running a servo sweep program through the Arduino IDE. By setting the power supply to 5V and observing the current draw during operation, we found the servo consumed a maximum of around 0.3A, resulting in a power usage of approximately 1.5W. This helped me understand how to monitor and calculate power consumption in practical setups.

    Output Devices

    An output device is a hardware component that receives data or commands from a microcontroller, processor, or computer and converts them into a form that humans can perceive or use. These devices translate electronically processed information into visual, auditory, or mechanical outputs to interact with the real world. This week I wanted to explore OLED display.

    OLED Display (Organic Light Emitting Diode)

    An OLED display is a small screen that produces its own light to show text and graphics. It is low power, easy to use with microcontrollers, and commonly connected using I2C (SDA, SCL).

    oled layer structure

    Source.

    How do OLEDs work?

    An OLED is a type of LED in which the emitting layer is made of organic compounds that produce light when an electric current is applied. The layer typically consists of a polymer substance sandwiched between two electrodes, a cathode, and an anode. When a current is applied, it causes the organic molecules to emit light.

    OLEDs work similarly to LEDs, but instead of using n-type and p-type semiconductor layers, they use organic compound layers to produce light.

    What makes OLED special?

    Why we use OLED in projects

    Common type used

    Basic connections

    Advantages of OLED

    Coin Vibration Motor (ERM)

    Coin Type Vibration Motor (ERM)

    A coin-type vibration motor is a compact actuator used to generate vibration in electronic devices. It works on the principle of an eccentric rotating mass (ERM), where a small unbalanced weight attached to a DC motor shaft rotates to produce vibration. Due to its flat and lightweight design, it is commonly used in wearable devices, mobile phones, and alert systems. In this project, the motor is used as an output device to provide haptic feedback and notification signals.

    Vibrator Inside

    Source.

     Working Principle

    Vibration strength depends on:

     Mechanical Specifications

    Parameter Typical Value
    Shape Flat Coin Type
    Diameter 8 mm 12 mm
    Thickness 2.5 mm 4 mm
    Weight ~3 grams
    Mounting Adhesive backing (double tape)

    Parameter Typical Value
    Rated Voltage 3V (2V,5V range)
    Current Consumption 60 100 mA
    Starting Voltage ~2V
    Speed ~10,000 RPM
    Control PWM supported

    Seeed Studio XIAO RP2040

    Overview

    The Seeed Studio XIAO RP2040 is a compact and powerful microcontroller board based on the RP2040 chip developed by Raspberry Pi. It features a dual-core ARM Cortex-M0+ processor and is designed for embedded systems, IoT devices, and wearable electronics. Due to its small size and high performance, it is widely used in modern electronics projects.

     Working Principle

     Mechanical Specifications

    Parameter Typical Value
    Board Size 21 mm A— 17.5 mm
    Weight ~2 grams
    Connector USB Type-C
    Mounting Castellated Pins / SMD Pads

    Electrical Specifications

    Parameter Typical Value
    Microcontroller RP2040 (Dual-core ARM Cortex-M0+)
    Operating Voltage 3.3V
    Input Voltage 5V via USB Type-C
    Clock Speed Up to 133 MHz
    Flash Memory 2 MB
    SRAM 264 KB
    GPIO Pins 11 multifunction GPIO
    ADC 12-bit (up to 4 channels)
    PWM Channels Up to 16
    Communication I2C, SPI, UART
    USB USB 1.1 (Device & Host)

    Pin Configuration

    Fabrication Notes

    Applications

    Pinout Diagram

    Source.

    NeoPixel LED (WS2812B)

    Source.

    Overview

    NeoPixel LEDs (WS2812B) are individually addressable RGB LEDs with an integrated driver chip. Each LED can display a wide range of colors and brightness levels using a single data line. They are widely used in interactive projects, decorative lighting, and embedded systems.

    Working Principle

     Mechanical Specifications

    Parameter Typical Value
    Package Type SMD 5050
    Size 5 mm A— 5 mm
    Mounting SMD / LED Strip / Module

    Electrical Specifications

    Parameter Typical Value
    Operating Voltage 5V
    Current (per LED) ~60 mA (max brightness white)
    Logic Voltage 3.3V 5V compatible
    Communication Single-wire digital protocol
    Control Signal PWM (internal)
    Data Rate ~800 kHz
    Color Type RGB (Red, Green, Blue)
    Color Depth 24-bit (16 million colors)

    Pin Configuration

    Fabrication Notes

    Applications

    I2C Connector (SMD JST Port)

    Overview

    The I2C connector is a compact Surface Mount Device (SMD) interface used to connect external modules such as OLED displays and sensors. It simplifies wiring by providing a standardized 4-pin interface for power and communication using the I2C protocol. This connector is widely used in embedded systems and modular electronics projects.

     Working Principle

     Mechanical Specifications

    Parameter Typical Value
    Connector Type JST / SMD Connector
    Mounting Type Surface Mount Device (SMD)
    Pin Count 4 Pins
    Pitch 1.0 mm 2.0 mm
    Orientation Right Angle / Top Entry
    Material Plastic Housing with Metal Contacts
    Color White / Beige
    Dimensions Approx. 5 mm A— 4 mm A 3 mm

    Electrical Specifications

    Parameter Typical Value
    Operating Voltage 3.3V / 5V
    Current Rating Up to 1A (typical)
    Communication Protocol I2C (Two-wire)
    Signal Lines SDA, SCL

    Pin Configuration

    Pin Function
    1 VCC (3.3V / 5V)
    2 GND
    3 SDA (Serial Data)
    4 SCL (Serial Clock)

    Fabrication Notes

    Applications

    Tactile Push Button Switch

    Note on Input Control

    Although this week focuses on output devices, a tactile push button was used in the design to control and switch between different output modes such as vibration patterns, LED effects, and display states. The button acts as a simple user interface to interact with the system.

    Working of MOSFET

    A MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) controls current flow between its source and drain terminals by varying the voltage applied to its gate. It consists of a semiconductor body with an insulating oxide layer separating the gate from the channel. When a voltage is applied to the gate, an electric field modifies the conductivity of the channel, allowing or restricting current flow. MOSFETs operate in two modes: enhancement mode, where no current flows without a gate voltage, and depletion mode, where a conductive channel exists by default and can be turned off with a gate voltage. There are two main types: N-channel MOSFETs, where electrons are the primary charge carriers and current flows when the gate is positively biased, and P-channel MOSFETs, where holes are the charge carriers and current flows when the gate is negatively biased. N-channel MOSFETs are generally preferred for high-speed and high-efficiency applications due to their lower resistance and faster switching characteristics.Here I am using an N-channel MOSFET.

    Source.

    Simple Explanation

    Part Function
    Gate (G) Control pin that receives signal from microcontroller
    Drain (D) Connected to load (motor/light)
    Source (S) Connected to ground
    Rin (Gate Resistor) Limits current from input signal and protects MOSFET
    Rgs (Pull-down Resistor) Keeps MOSFET OFF when no input signal is present
    Working (ON State) When input voltage is HIGH, MOSFET turns ON and current flows from drain to source, powering the load
    Working (OFF State) When input is LOW, MOSFET turns OFF and stops current flow

    Designing PCB in KiCad

    The circuit uses a XIAO RP2040 as the main controller, along with a MOSFET to drive a vibration motor, a Schottky diode for protection, a NeoPixel (WS2812B) LED for visual output, resistors for signal stability, a push button for input, and an I2C connector to connect devices like an OLED display.

    This circuit uses an N-channel MOSFET to control a vibration motor from a microcontroller signal. A Schottky diode is added across the motor to protect the circuit from reverse voltage spikes.

    This is a NeoPixel (WS2812B) RGB LED connected to 5V and GND, controlled by a single data pin from the microcontroller. It can display different colors based on the signal received.

    This is an I2C connector with 4 pins: VCC (3.3V), GND, SDA, and SCL. It is used to connect devices like an OLED display or sensors to the microcontroller.

    This is a touch pad input connected to the microcontroller, where touching the pad changes the signal. The resistor to ground helps stabilize the signal and detect touch properly.

    This is an SMD XIAO RP2040 microcontroller module, which acts as the main control unit of the circuit. It reads inputs (button/touch) and controls outputs like the motor and NeoPixel LED using its GPIO pins.

    This is a push button switch with a pull-up resistor, where the resistor keeps the signal HIGH and pressing the button connects it to GND (LOW). It is used as a simple input for the microcontroller.

    This is a 4-pin SMD header (I2C interface) providing 3.3V, GND, SDA, and SCL connections. It is used to easily connect external modules like sensors or an OLED display.

    These constraints settings in KiCad define the minimum values for track width, spacing, via size, and clearances to ensure the PCB is manufacturable and avoids short circuits or design errors.

    These PCB tracks are copper paths that connect all components like the XIAO RP2040, MOSFET, NeoPixel, and connectors, allowing signals and power to flow through the circuit. The routing is done carefully to avoid overlap, maintain spacing, and ensure reliable connections.

    Use ruleschecker to verify the connections. Now we have to change the file to gerber format. Then I uploded the gerber files in Gerber to png. software to convert it to PNG format. For double layer PCB we have five layers to mill.

    PCB Output

    Milling the PCB

    The Roland Modela MDX-20 machine is used for PCB milling. We need to manually set the zero position (X, Y, and Z axes). Load the 1/64" engraving bit and set the X and Y axes at a corner of the board. Then, lower the bit slowly until it just touches the PCB surface and set Z = 0. After that, upload the top trace layer, calculate the toolpath, and send the file to the machine for milling.

    After milling the first layer, carefully replace the bit to 1/32" drill bit for vias, holes and outline cuts.Re-zero only the Z-axis, keeping X and Y unchanged. Resume milling.

    Load the engraving bit and zero the Z-axis again. Run the bottom layer trace milling. Then change the bit.Cut the PCB outline using 1/32" end mill. Here is the final result.

    Assembling the components

    I requested the components from fabstash and collected it from the inventory. I used ineractive HTML BOM in KiCad to get the list of components. It is also highlights were to place components in the pcb.

    The following components were used to design and fabricate the PCB for the vibration feedback system:

    Note: The image was partially masked because some component labels were incorrectly written during selection. The masking was done to avoid confusion.

    The PCB was assembled by soldering all components

    Inspecting the PCB

    The first step is microscope inspection, which focuses on visually examining the PCB for physical defects. Check for issues such as poor solder joints, solder bridges, cracked components, or broken traces. Ensure that all components are correctly placed and aligned.

    Testing

    The PCB was tested for short circuits and voltage drops using a USB tester and power supply.The circuit worked properly with stable voltage and no short circuit issues.

    Programmming the PCB

    Code Reference

    This code was developed with the assistance of ChatGPT. 

    #include 
#include 
#include 

#define SCREEN_WIDTH 128
#define SCREEN_HEIGHT 32

#define SDA_PIN D4
#define SCL_PIN D5
#define BUTTON_PIN D7
#define MOTOR_PIN D2

Adafruit_SSD1306 display(SCREEN_WIDTH, SCREEN_HEIGHT, &Wire, -1);

int mode = 1;
bool lastButtonState = HIGH;

unsigned long pressStart = 0;
int intensity = 80;

void setup() {
  pinMode(BUTTON_PIN, INPUT_PULLUP);
  pinMode(MOTOR_PIN, OUTPUT);

  Wire.setSDA(SDA_PIN);
  Wire.setSCL(SCL_PIN);
  Wire.begin();

  display.begin(SSD1306_SWITCHCAPVCC, 0x3C);
  display.setRotation(1);  // portrait

  display.clearDisplay();
  updateDisplay();
}

void loop() {
  bool buttonState = digitalRead(BUTTON_PIN);

  if (lastButtonState == HIGH && buttonState == LOW) {
    pressStart = millis();
  }

  if (lastButtonState == LOW && buttonState == HIGH) {
    unsigned long pressTime = millis() - pressStart;

    if (pressTime > 800) {
      if (mode != 4) {
        intensity += 30;
        if (intensity > 255) intensity = 80;
      }
    } else {
      mode++;
      if (mode > 4) mode = 1;

      if (mode == 1) intensity = 80;
      if (mode == 2) intensity = 150;
      if (mode == 3) intensity = 255;
      if (mode == 4) intensity = 0;
    }

    updateDisplay();
    delay(200);
  }

  lastButtonState = buttonState;

  analogWrite(MOTOR_PIN, intensity);
}

void updateDisplay() {
  display.clearDisplay();
  display.setTextColor(WHITE);

  int16_t x1, y1;
  uint16_t w, h;

  // 🔹 MODE (small)
  display.setTextSize(1);
  String title = "MODE";
  display.getTextBounds(title, 0, 0, &x1, &y1, &w, &h);
  int xTitle = (32 - w) / 2;

  // 🔹 NUMBER (big)
  display.setTextSize(2);
  String text = (mode == 4) ? "0" : String(mode);
  display.getTextBounds(text, 0, 0, &x1, &y1, &w, &h);
  int xNum = (32 - w) / 2;

  // 🔥 vertical center
  int startY = 40;

  // Draw
  display.setTextSize(1);
  display.setCursor(xTitle, startY);
  display.println(title);

  display.setTextSize(2);
  display.setCursor(xNum, startY + 12);
  display.println(text);

  display.display();
}

    Hero Shot

    Mistakes

    Conclusion

    This project demonstrates the integration of a vibration motor, OLED display, and button control using the XIAO RP2040. Different vibration modes were implemented using PWM, with a clear and user-friendly interface on the OLED. Overall, it helped in understanding embedded system design, hardware control, and UI development.

    Useful Links

    Tools & Technologies Used

    The programming for this project was developed using Arduino IDE .

    The PCB for this project was designed using KiCad , an open-source electronic design automation (EDA) tool.

    AI tools such as ChatGPT were used to assist in generating code, debugging, and improving documentation.

    Download Files

    Download ZIP File