Week 09 | Input Devices

In this week’s assignment, the objective was to work with input devices, meaning sensors that allow the microcontroller to receive information from the environment. For this exercise, I decided to work with a PIR sensor (Passive Infrared Sensor), which detects motion from people or warm objects through changes in infrared radiation.

The purpose of this exercise was to understand how to read digital signals from a sensor using the XIAO ESP32C3 board and the Arduino IDE environment, as well as to better understand the relationship between the electronic circuit and programming.

1. Electronic Board

In this week, I used a custom electronic board that functions as the base of the system. The board was designed in KiCad, starting from the schematic design and then moving to the PCB layout.

The board is based on a XIAO ESP32 microcontroller, selected for its compact size and its processing and communication capabilities. The power lines (VBUS and GND) were clearly defined and strategically distributed to facilitate the connection of multiple components.

The board includes:

• 1kΩ resistors for current limiting in outputs
• 10kΩ resistors used as pull-down or pull-up resistors in inputs
• Header connectors for sensors and actuators
• Accessible pads to simplify testing and measurements

The routing was done on a single side, optimizing trace paths and avoiding crossings, which is essential for CNC milling. A trace width of 0.4 mm and proper spacing were carefully considered to ensure a clean fabrication process.

The board was manufactured by milling a copper-clad board, followed by manual drilling and THT component soldering. Finally, continuity was checked with a multimeter and the basic functionality of the circuit was validated.

Based on this platform, input devices were connected and tested. Since the board already had defined input pins and integrated resistors for signal stability, it was possible to connect devices such as a PIR sensor and a switch without redesigning the hardware.

2. Working Principle

PIR Sensor

The sensor has three pins:

• VCC (power supply)
• GND (ground)
• OUT (digital signal)

The sensor output is digital:

• 0 → No motion detected
• 1 → Motion detected

This type of sensor is very useful for interactive systems, automatic lighting, security systems, and interactive installations.

Sensor Connection to the Microcontroller

To connect the PIR sensor to the XIAO ESP32C3 board, the following connections were used:

It is important to power the sensor with 5V and share the ground with the microcontroller so that the digital signal can be read correctly.

3. Programming and Data Reading

Arduino IDE was used to program the XIAO ESP32C3 board. The program reads the state of the digital pin connected to the sensor and sends the value to the Serial Monitor so the changes can be observed in real time.

Code used:

#define PIR_PIN D4

	void setup() {
	Serial.begin(115200);
	pinMode(PIR_PIN, INPUT);
	}

	void loop() {
	int state = digitalRead(PIR_PIN);
	Serial.println(state);
	delay(200);
						}

This program makes it possible to visualize values of 0 and 1 in the Serial Monitor depending on whether the sensor detects motion or not.

4. Testing and Debugging Process

During the testing process, it was necessary to verify several aspects:

1. Correct Arduino IDE configuration for the XIAO ESP32C3 board.
2. Selection of the correct COM port.
3. Verification of the sensor power supply.
4. Checking the digital pin connection.
5. Using the Serial Monitor to verify the sensor readings.
6. Resetting the board when the port was busy or when uploading failed.

I also learned that the PIR sensor requires a stabilization time after powering on (approximately 30–60 seconds), during which it may provide inaccurate readings.

5. Results

After making the connections and uploading the program, it was possible to observe in the Serial Monitor that:

• When there was no motion, the sensor sent a value of 0.
• When motion was detected in front of the sensor, the value changed to 1.

This confirms that the sensor works correctly as a digital input device.

Learning Outcomes

In this part of the assignment, I learned:

• How to connect a digital sensor to a microcontroller.
• How to read digital signals using Arduino.
• The difference between input and output devices.
• The importance of power supply and ground connections.
• How to use the Serial Monitor to debug electronic systems.
• That many errors are not related to programming, but to electrical connections.
• The importance of testing the microcontroller first and then the sensor.
• The debugging process in embedded systems.

This exercise is important because it builds the foundation for interactive systems, where the microcontroller must react to information from the environment provided by sensors.

Conclusion

Working with the PIR sensor and the XIAO ESP32C3 board made it possible to understand how digital input devices work and the complete process from electronic connection to data reading through programming. This knowledge will be fundamental for the development of the final project, where sensors will be integrated to generate interactions with actuators and mechanical systems.

Download Files

The design files used in this assignment can be downloaded below.

• Download KiCad
• Download SVG
• Download Arduino