Week 10 – Output devices

Project Overview – Motor Control with HC-SR04

In this project, a proximity detection system is developed using the HC-SR04 ultrasonic sensor and the XIAO ESP32-C3 microcontroller to control a 5V DC motor. The system uses distance measurements to activate or deactivate the motor through an L298N motor driver module.

When an object is detected within a defined range, the motor is activated. Otherwise, it remains off. This demonstrates how sensor signals can be used to control output devices in real-time embedded systems.

System Functionality

• Distance < 15 cm → Motor ON
• Distance ≥ 15 cm → Motor OFF

Bill of Materials

Key Considerations

• The motor is controlled via the L298N driver, not directly from the microcontroller
• Ensure common ground between all components
• Verify correct voltage levels for safe operation

Schematic Design – Step by Step

The schematic design defines how all components are electrically connected. This system integrates an ultrasonic sensor (HC-SR04), a motor driver (L298N), a DC motor, and the XIAO ESP32-C3 microcontroller.

Step 1: Power Distribution

• Connect GND of all components together (common ground)
• Provide 5V to the HC-SR04 and L298N module
• The XIAO ESP32-C3 operates at 3.3V logic

🔌 Step 2: HC-SR04 Connections

Important: Use a voltage divider on the ECHO pin if needed to reduce from 5V to 3.3V.

Step 3: L298N Motor Driver Connections

Step 4: Motor Connection

The DC motor is connected to the output terminals of the L298N driver module. This module acts as an interface between the microcontroller and the motor, allowing safe control of direction and power.

Connection Steps

• Locate the output terminals on the L298N labeled OUT1 and OUT2
• Connect one wire of the motor to OUT1
• Connect the other wire of the motor to OUT2

The motor does not have polarity restrictions for basic operation. However, swapping the wires will reverse the rotation direction.

How Direction Control Works

IN1	IN2	Motor Behavior
HIGH	LOW	Rotation Direction 1
LOW	HIGH	Rotation Direction 2
LOW	LOW	Motor Stop

Important Considerations

• The motor must be powered through the L298N module, not directly from the microcontroller
• Ensure the motor power supply (5V) is properly connected to the L298N
• All grounds (XIAO, L298N, power supply) must be connected together
• Verify that the ENA jumper is enabled or connected to 5V for activation

Step 5: Logic Behavior

• IN1 = HIGH, IN2 = LOW → Motor rotates forward
• IN1 = LOW, IN2 = HIGH → Motor rotates reverse
• IN1 = LOW, IN2 = LOW → Motor stops

Key Design Considerations

• Ensure all grounds are connected together
• Do not power the motor directly from the microcontroller
• Use stable external power for the motor if required
• Verify voltage compatibility between components

Code Description – Ultrasonic Sensor + Motor Control

This program uses an ultrasonic sensor (HC-SR04) to measure distance and control a DC motor based on proximity. When an object is detected within a defined range, the motor is activated.

Pin Configuration

Program Workflow

• Initialize serial communication for monitoring data
• Configure TRIG as output and ECHO as input
• Set motor control pin as output
• Send a 10 microsecond pulse to trigger the sensor
• Measure the duration of the echo signal
• Calculate the distance using the speed of sound
• Activate the motor if the object is closer than 15 cm
• Print distance data to the serial monitor

Distance Calculation

The distance is calculated using the time it takes for the ultrasonic wave to travel to the object and return:

Distance = (Time × Speed of Sound) / 2

Motor Control Logic

Key Considerations

• Ensure correct timing for the trigger pulse (10 microseconds)
• Use a common ground for all components
• Verify stable power supply for the motor
• Adjust distance threshold based on application needs

Code Implementation

// Pin Configuration
const int TRIG_PIN = 4;
const int ECHO_PIN = 5;
const int MOTOR_PIN = 6;

void setup() {
  Serial.begin(115200);
  
  pinMode(TRIG_PIN, OUTPUT);
  pinMode(ECHO_PIN, INPUT);
  pinMode(MOTOR_PIN, OUTPUT);
}

void loop() {
  long duration;
  float distance;

  // Trigger pulse
  digitalWrite(TRIG_PIN, LOW);
  delayMicroseconds(2);
  digitalWrite(TRIG_PIN, HIGH);
  delayMicroseconds(10);
  digitalWrite(TRIG_PIN, LOW);

  // Read echo
  duration = pulseIn(ECHO_PIN, HIGH);

  // Distance calculation
  distance = (duration * 0.0343) / 2;

  // Motor control
  if (distance < 15) {
    digitalWrite(MOTOR_PIN, HIGH); // Motor ON
  } else {
    digitalWrite(MOTOR_PIN, LOW); // Motor OFF
  }

  Serial.print("Distance: ");
  Serial.println(distance);

  delay(100);
}
    

FabXIAO Output Connections

Before running the bidirectional motor test, the FabXIAO board was connected to the L298N driver and checked as the control interface for the output device. The XIAO ESP32-C3 sends only logic signals, while the L298N receives external motor power and switches the motor terminals safely.

This wiring evidence shows the custom PCB being used as the controller board for the output test. The motor driver is separated from the FabXIAO so that the high-current side of the system does not pass through the microcontroller.

Evidence of the FabXIAO PCB used as the control board for the output device test.

Bidirectional Motor Control Using Time Intervals

This implementation demonstrates how a DC motor can rotate in both directions (left and right) by controlling the logic states of a motor driver (L298N). By alternating the control signals with defined time intervals, the motor changes direction automatically every few seconds.

This approach is commonly used in automation systems where periodic motion is required, such as conveyor belts, oscillating mechanisms, or scanning devices.

Pin Configuration

Connection Details

• Connect motor terminals to OUT1 and OUT2 of the L298N module
• Connect IN1 to D4 and IN2 to D5 on the XIAO ESP32-C3
• Ensure the ENA pin is connected to 5V or enabled with a jumper
• Provide 5V external power to the L298N motor supply
• Connect all grounds together (XIAO, L298N, and power supply)

Motor Control Logic

Code Implementation

// DC Motor Bidirectional Control with Time Intervals

const int IN1 = 6; // D4
const int IN2 = 7; // D5

void setup() {
  pinMode(IN1, OUTPUT);
  pinMode(IN2, OUTPUT);
}

void loop() {

  // Rotate in one direction
  digitalWrite(IN1, HIGH);
  digitalWrite(IN2, LOW);
  delay(3000);

  // Rotate in opposite direction
  digitalWrite(IN1, LOW);
  digitalWrite(IN2, HIGH);
  delay(3000);
}
    

Key Concept

By alternating the logic levels of IN1 and IN2 with time delays, the motor reverses its rotation direction. This creates a continuous left-to-right motion cycle without requiring additional sensors or feedback systems.

Problems During Servo Tests and Lessons Learned

During the output device tests, several servos were damaged while trying to validate actuator movement for the final project. This was an important part of the process because it showed that an actuator can fail even when the code logic seems correct. The problem was related to power distribution, wiring verification, and the difference between a control signal and the current required by the actuator.

After these tests, the decision was made not to continue using servos for this mechanism. The final project requires moving a conveyor belt, so the actuator selected for the next development stage is a 12V DC motor. This change is also the preamble for the Machines Design assignment, where the belt system, motor power, transmission, and mechanical integration will be developed in more detail.

What Happened

• Some servos overheated during repeated movement tests.
• In some trials, the servo stopped responding after being connected to an unstable power setup.
• The tests showed that powering an actuator from an inadequate source can damage the component.
• Shared ground was necessary, but the power line for the actuator also needed to be checked independently.

Probable Causes

Learning Outcome

The damaged servos helped define a safer workflow for future actuator tests: first test the board without the actuator, then verify voltage and continuity, then connect the actuator with an external power supply, and finally test the movement with short commands before running a full cycle. This lesson is directly connected to the final project, where the modular cell will require reliable actuation and safe power distribution. For the next stage, the work will focus on controlling a 12V DC motor because it is more appropriate for driving a conveyor belt than a small servo.

Evidence of the damaged servo used during the output device tests.

Reflections

This assignment provided a comprehensive understanding of how output devices behave in real electrical systems, particularly in terms of power consumption. By integrating a DC motor with a microcontroller and a motor driver, we were able to move beyond theoretical concepts and directly observe how voltage, current, and control logic interact in practice.

One of the key learnings was the correct use of measurement instruments. We reinforced the importance of measuring voltage in parallel and current in series, as well as understanding how polarity changes when controlling bidirectional systems using an H-bridge. This helped us interpret negative values not as errors, but as indicators of direction changes.

Additionally, we developed a clearer understanding of how power is calculated and how even small variations in voltage and current can impact overall system performance. The process of calculating real power consumption allowed us to validate theoretical formulas with actual measurements.

From a system integration perspective, we also learned the importance of proper wiring, stable power supply, and the role of drivers like the L298N in protecting the microcontroller while enabling control of higher power devices.

Overall, this assignment strengthened our ability to analyze and design embedded systems, bridging the gap between electronics theory and practical implementation. It also emphasized the importance of accurate measurement and documentation in engineering workflows.