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Week 10 Assignments - Output Devices

Group Assignment

The group assignment for this week was to:

  • Measure the power consumption of an output device.
  • Document your work on the group work page and reflect on your individual page what you learned.

Outcomes

The group assignment page for this week is on the 2025 Charlotte Super Fab Lab group site for Week 10 - Output Devices.

What Was Learned

In the group assignment, we considered power consumption of LEDs - including one standard LED and 2 neopixels. We were able to measure the power consumption for the LEDs across different RGB settings to drive the individual R, G, and B component channels. This provided us experience on:

  • How to use test equipment to measure power consumption
  • What to look for in power consumption as part of assignments and project work going forward

Individual Assignment

The individual assignment for this week was to:

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

Outcomes

In order to explore different outputs, I used the microcontroller board that I developed previously in Week 8 - Electronics Production.

I selected an LED and a servo motor to test as outputs. The LED was integrated onboard as part of the previouly completed development board. The servo motor used direct connections to the input connectors on the development board.

Integrated LED

The LED connection was integrated into the design of the Xiao ESP32C3 microcontroller board that I designed. One side of the LED has a connection to the XIAO board on pin D6 (GPIO21). This connection serves provides a driving voltage for the LED. The other side of the LED is connected to a 50 ohm resistor, as appropriate for the LED, with 3.3V XIAO power. The XIAO can then drive the state of the LED with output on pin D6 (HIGH for on, and LOW for off).

I wrote a program from scratch using C code and the Arduino IDE, in order to exercise the onboard LED. There are two main parts.

  • Blink the LED 5 times on setup - in general, this can be a useful visual signal to know that our program has loaded and is starting on the board and may be helpful to include in other programs later
  • Connect the state of the LED to the onboard pushbutton that was developed in the Week 9 Assignments - Input Devices. When the button is not pressed, the onboard LED is off. When the button is pressed, the onboard LED is on.
Onboard LED Output - Startup and Button Response
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// Define the XIAO Pins in Use

const int onboardLEDPin = D6;
const int onboardButtonPin = D7;

// Run Once at the Start
void setup() {

  // Set onboard LED pin as output
  pinMode(onboardLEDPin, OUTPUT);

  // Blink the onboard LED 5 times
  // Confirm that we are getting setup
  for (int i=0; i<5; i++)
  {
    digitalWrite(onboardLEDPin,LOW);
    delay(250);
    digitalWrite(onboardLEDPin,HIGH);
    delay(250);
  }
  digitalWrite(onboardLEDPin,LOW);

  // Set onbarod button pin as input
  pinMode(onboardButtonPin,INPUT); 
}

// Run Repeatedly
void loop() {

  // If the button is pressed, turn on LED
  // Otherwise, turn off LED
  int buttonState = digitalRead(onboardButtonPin);
  if (buttonState == HIGH)
  {
    digitalWrite(onboardLEDPin,HIGH);
  }
  else
  {
    digitalWrite(onboardLEDPin,LOW);
  }

}

Onboard LED - Blink Sequence on Startup and Button Lightup Response

Servo Sweep with LED Transition

For the second output device, I selected a micro servo. I developed a progam that sweeps the servo position back and forth continuously. When a sweep in a particular direction reaches the end, the onboard LED blinks once to indicate the transition to the other direction.

I connected the servo to the XIAO board using the input connectors, as follows:

  • The servo power lead (red wire) was connected to the XIAO 5V output
  • The servo GND lead (brown wire) was connected to the XIAO GND output
  • The servo signal lead (orange wire) was connected to the XIAO output pin D10

I wrote the servo control program in C using the Arduino IDE. The Arduino IDE provides a set of example programs for outputs. I adapted the Sweep example program to control the servo motor. A number of revisions and modifications were made.

The example program used the Servo.h library as support to control the servo motor. Compiling the program gave a number of errors related to the library. I conducted some basic research and found that a special version of the servo library is needed for ESP32 type boards. I located the correct library ESP32Servo.h and installed it in the Arduino IDE.

To signal the end of a sweep in one direction and a change to a sweep in the opposite direction, I added a blink of the onboard LED after the end of each sweep.

Servo Sweep with LED Transition
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#include <ESP32Servo.h>

Servo myservo;  // create servo object to control a servo
// twelve servo objects can be created on most boards

int pos = 0;    // variable to store the servo position

void setup() {
  myservo.attach(D10);  // attaches the servo on pin 9 to the servo object
  pinMode(D6,OUTPUT);
  digitalWrite(D6,LOW);
}

void loop() {
  for (pos = 0; pos <= 180; pos += 1) { // goes from 0 degrees to 180 degrees
    // in steps of 1 degree
    myservo.write(pos);              // tell servo to go to position in variable 'pos'
    delay(15);                       // waits 15 ms for the servo to reach the position
  }
  digitalWrite(D6,HIGH);
  delay(100);
  digitalWrite(D6,LOW);
  for (pos = 180; pos >= 0; pos -= 1) { // goes from 180 degrees to 0 degrees
    myservo.write(pos);              // tell servo to go to position in variable 'pos'
    delay(15);                       // waits 15 ms for the servo to reach the position
  }
  digitalWrite(D6,HIGH);
  delay(100);
  digitalWrite(D6,LOW);
}

Servo Sweep with LED Blink on Direction Change