This week focuses on sensing physical input using electronic input devices and a microcontroller board.
The goal is to understand how physical interaction is translated into digital signals, how those signals are read by a microcontroller, and how they can be observed, processed, and debugged.

For this assignment, I used the custom PCB I designed for my final project and interfaced four push buttons as digital input devices.

Learning Outcomes

• Demonstrate workflows used in sensing physical input with input device(s) and a microcontroller
• Probe and interpret digital signals generated by input devices
• Implement firmware to reliably read and process input signals

1. Introduction

Input devices allow physical phenomena, such as pressing a button to be converted into electrical signals that a microcontroller can interpret.

In this assignment, I measured discrete user input using four push buttons connected directly to my custom ESP32-C3 PCB.

Each button generates a digital signal (HIGH/LOW), which I read using internal pull-up resistors and processed in firmware.

2. Input Device Selection

Push Buttons (Digital Input)

Each push button functions as a momentary switch:

• Pressed → circuit closes → GPIO pulled LOW
• Released → circuit open → GPIO pulled HIGH (via pull-up)

Why Buttons?

• Simple, reliable digital input
• Easy to probe and debug
• Ideal for demonstrating digital signal behavior
• Commonly used in embedded systems

3. Custom PCB

All input devices are connected directly to a custom PCB.

Board Used

• Final Project PCB
• Designed and documented in Week 6 — Electronics Design
• Microcontroller: ESP32-C3 Super Mini

➡️ Board design details, schematic, and PCB layout are fully documented in Week 6.

Button Wiring (On PCB)

Each button is wired as follows:

• One side → GPIO pin
• Other side → GND
• Internal pull-up enabled in firmware

GPIO Mapping

This configuration ensures a clean digital signal without external resistors.

4. Probing the Input Device

What Does “Probe an Input Device” Mean?

Probing means observing the electrical signal produced by a sensor or input device using test equipment.

How I Probed the Buttons

I probed the buttons using:

• Multimeter (voltage & continuity mode)
• Serial monitor output (logical probing)

Observations

This confirms:

• Internal pull-ups are working correctly
• Buttons generate clean digital transitions
• No floating inputs are present

5. Firmware & Programming

Programming Environment

• Arduino IDE
• Board core: ESP32-C3
• Communication: USB Serial (UART)

Firmware Strategy

Key concepts implemented:

• Internal pull-up resistors
• Digital input reading
• Edge detection
• Software debouncing
• Serial feedback

Code Overview

GPIO Assignment

int buttons[] = {2, 6, 4, 3};
const char* labels[] = {"Option A", "Option B", "Option C", "Option D"};
int lastState[4];

• Buttons stored in an array for scalable logic
• Labels used for readable serial output
• lastState[] tracks previous button states

Setup Phase

void setup() {
  Serial.begin(115200);
  delay(500);

  for (int i = 0; i < 4; i++) {
    pinMode(buttons[i], INPUT_PULLUP);
    lastState[i] = HIGH;
  }
}

What this does:

• Enables internal pull-ups
• Ensures default HIGH state
• Prevents floating inputs
• Initializes serial communication

Loop Logic (Edge Detection + Debounce)

int current = digitalRead(buttons[i]);

if (current == LOW && lastState[i] == HIGH) {
  delay(10);
  if (digitalRead(buttons[i]) == LOW) {
    Serial.print(labels[i]);
    Serial.println(" pressed!");
    lastState[i] = LOW;
  }
}

Why this matters:

• Detects new presses only
• Prevents repeated triggers
• Handles mechanical bouncing
• Ensures stable readings

6. Demo & Results

The video below shows the demo:

Problems & Fixes

Issue 1 — Button Bounce

Symptom:

• Single press registered multiple times.

Fix:

• Added 10 ms debounce delay
• Implemented edge detection

Issue 2 — Floating Inputs (Early Test)

Symptom:

• Random button presses detected.

Fix:

• Enabled INPUT_PULLUP
• Verified ground continuity
• Probed voltage levels

6. Group Project

You can check our group project here

7. Files

• Download Source Code
• PCB Design: See Week 6 — Electronics Design

8. Reflection

This assignment strengthened my understanding of human–machine interaction at the electrical level. Even a simple button requires careful consideration of signal stability, hardware design, and firmware logic.

By using my own PCB, probing real signals, and writing debounced firmware, I demonstrated a complete and correct input-device workflow, fully aligned with Fab Academy expectations.