10. Output
Devices

Group assignment

This week focused on understanding and testing output devices. Outputs are components that convert an electrical signal from a microcontroller into a physical, visual, or auditory action. I researched motor types, selected a servo motor, and wrote a program to test its movement as part of my kinetic origami final project.

Tasks:

★

Add an output device to a microcontroller board you have designed and program it to do something.


Research

Output Devices

Output devices convert the electrical signal from a microcontroller into a physical, visual, or auditory action.

I started by reviewing Ohm's and Kirchhoff's Laws to build a solid foundation before working with output devices.

Canva notes summarizing Ohm's Law and Kirchhoff's Law review for the output devices week
Ohm's and Kirchhoff's Law review.

I then went deeper into output devices and also reviewed my Week 4 — Embedded Systems Map, which helped me recall the different categories of output devices.

Week 4 outputs

Motor Info

I found motors particularly interesting, so I began researching how they operate in more depth. I focused on a few core concepts and started by creating a mind map to understand the different types of actuators available and the situations they are best suited for.

Mind map showing the different types of actuators and their best use cases
Mind map — Types of actuators and their applications.

Why you cannot connect a motor directly to a microcontroller

Based on Ohm's and Kirchhoff's laws reviewed in Week 6, connecting a motor directly to a microcontroller pin is not possible. The motor will attempt to draw more current (amps) than the microcontroller pins can supply, which causes the board to overheat and fail.

To prevent this, external components must be used as a bridge. These vary depending on the motor type:for example, MOSFETs for DC motors or dedicated driver ICs for stepper motors. I did another diagram to see wich one is used for each motor.

Mind map showing the external driver modules required for each motor type in order to protect the microcontroller from overcurrent
Mind map — External modules required for each motor type.

Why I Chose a Servo

Since my final project involves a kinetic origami panel that reacts to air quality, I needed to decide between a standard DC motor and a servo for the folding mechanism. Because the design does not require continuous rotation speed control — but instead demands reasonably precise angular movement to fold and unfold the structure — a servo is the better choice.

ADVANTAGES OF THE SERVO

  • Precise angular position control without needing continuous rotation feedback.
  • More energy-efficient than a stepper motor — it does not drain a large amount of current just to hold its position.
  • Has an internal controller, which simplifies the external circuit significantly.

CONSIDERATION

  • Standard servos are limited to a 180-degree rotation range.
  • If a wider angle is needed for the origami folds, a custom gear ratio can be implemented to extend the effective range.

Connecting

Connecting a servo is straightforward because it already has an internal controller. It uses three wires.

Servo Wiring — Three Wires

Power (VCC) — Connected to the 5 V power supply.

Ground (GND) — Connected to the common ground of the circuit.

Signal — Connected directly to a digital PWM pin on the microcontroller.

MG995 Datasheet

To connect the servo correctly, I consulted the MG995 datasheet, where I found its pinout.

MG995 servo motor pinout diagram from the official datasheet showing the VCC, GND, and PWM signal wire color assignments
MG995 pinout — from the official datasheet.

PCB Pin Verification

I also checked the XIAO Pinout to confirm I was using the correct pins before making the connections.

PCB design file screenshot showing the pin layout and confirming the correct PWM output and power pins for the MG995 servo connection
PCB file — pin reference used for wiring.

FINAL CONNECTIONS — MG995 → PCB

  • MG995 VCC → PCB Power
  • MG995 GND → PCB GND
  • MG995 PWM → PCB Pin D0

Programming

Once the hardware was connected, I programmed the XIAO RP2350 using Arduino IDE to read the live acceleration values from the MPU6050. The first step was to connect the PCB to Arduino IDE.


CONNECTION PROCESS:


I installed the servo Library:

ServoLib

To control the servo, I used Pulse Width Modulation (PWM) to send signals to the motor's internal controller, telling it exactly which angle to move to. The goal of the test code was to make the servo sweep back and forth to simulate the folding motion of the origami.

Source Code

#include <Servo.h>

Servo miMotor;
int pinServo = 0;
int pinBoton = 7;

void setup() {

  miMotor.attach(pinServo);
  miMotor.write(0);

  pinMode(pinBoton, INPUT_PULLUP);
}

void loop() {
  if (digitalRead(pinBoton) == LOW) {

    miMotor.write(90);
    delay(500);

    miMotor.write(180);
    delay(500);

    miMotor.write(0);
    delay(500);
  }

  delay(50);
}

Code Breakdown

Libraries & Variables

  • #include <Servo.h> — imports the Arduino Servo library, which provides all the functions needed for PWM-based motor control.
  • Servo miMotor — creates the Servo object that will be used to issue movement commands throughout the program.
  • pinServo = 0 — defines pin D0 as the PWM signal output to the motor.
  • pinBoton = 7 — defines pin D7 as the digital input for the push button.

Setup

  • miMotor.attach(pinServo) — links the Servo object to pin D0 so that write() commands generate the correct PWM waveform on that pin.
  • miMotor.write(0) — moves the servo to the 0° start position on power-up, ensuring a known initial state.
  • INPUT_PULLUP — activates the microcontroller's internal pull-up resistor on the button pin. The pin reads HIGH (1) normally and LOW (0) when the button is pressed and connected to GND.

Loop — Button Check

  • digitalRead(pinBoton) == LOW — checks whether the button is currently being pressed. Because of INPUT_PULLUP, a press pulls the pin to GND (LOW), triggering the condition.

The sweep routine runs only while the button is held. This makes the test repeatable and isolated from the rest of the program.

Sweep Routine

  • miMotor.write(90) — moves the servo to the center position (90°).
  • miMotor.write(180) — moves the servo to its maximum angle (180°).
  • miMotor.write(0) — returns the servo to the initial position (0°).
  • delay(500) — pauses 500 ms between each movement, giving the servo enough time to reach the target angle before the next command is issued.

Stability Pause

  • delay(50) — a short pause at the end of each loop iteration. It reduces the button polling rate and prevents erratic readings caused by contact bounce.

Final Result

After uploading the code and connecting the power supply, the servo successfully moved to the programmed angles. Testing this output in isolation from the rest of the project provided the confidence needed to integrate it into the final kinetic structure.

Final Reflection:

During this week it was very interesting learning about the motors, thanks to this weeks I got to understand the electricity laws better.