Fab Academy 2026 | Week 09

Assignment requirements

Group assignment

Test an input device(s)'s analog levels and digital signals (As a minimum, you should demonstrate the use of a multimeter and an oscilloscope
Document your work on the group work page and reflect on your individual page what you learned

Individual assignment

Measure something: add a sensor to a microcontroller board that you have designed and read it

Progress status

Group work Done

Test an input device analog levels and digital signals

Individual work In progress

Add a sensor to a microcontroller board that you have designed and read it

Documentation Done

Upload source files.

1) Introduction

Closing gaps

Learn about input devices
Interact more with Arduino IDE
Discuss the group project
Develop the individual project

2) Group assignment 1 - Test an input devices (analog & digital)

For more details visit Fab Lab Peru Week 9 Group assignment

Project - Ultrasonic Sensor - Digital

Ultrasonic Sensor HC-SR04

Group Assignment - Input Devices (Analog & Digital)

Project idea

Ultrasonic HC-SR04 sensor module
Measures distance using sound waves
Includes transmitter and receiver
Range: 2 cm to 500 cm
Pins: Vcc, Trig, Echo, GND

Video demonstration

3) Group assignment 2 - Test an input devices (analog & digital)

More information at Fab Lab Peru - Group Assignment: https://fabacademy.org/2026/labs/lima/#page-top

Project - LM 393 Photosensitive light dependent resistor (LDR)

LM 393 Photosentitve light dependent resistor (LDR)

Group Assignment - Input Devices (Analog & Digital)

Project idea

Distance detection
Driving ability - 15mA with adjustable potentiometer
Brightness - Adjustable
Detect - brightness and light intensity
Analog and digital output

Video demonstration

4) Individual assigment

Problems

Designed microcontroller board doesn't work

Posible solution - make a new board

Step 1 - Protoboard

Mesasure something with the microcontroller Xiao ESP32 C3

Step 2 - Repeat with a new board

Measure and test devices using a multimeter or an oscilloscope

Reviewing the Xiao ECP32 C3, technical specitications and connections

This Wiki was useful https://wiki.seeedstudio.com/xiao_esp32s3_getting_started/

Select the TCRT5000L reflective optical sensor

Emitter Wavelength: 950 nm - infrared

Xiao ECP 32 C3 Connections

New installation - download ECP 32 C3 libraries

// TCRT5000L reflective optical sensor
            // Input devices 
            // Board: Seeed Studio XIAO ECP 32 C3

            #define sensor = D6;   // cambia al GPIO/pin que uses

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

            void loop() {
                  int val = digitalRead(sensor);
                  Serial.println(val);
                  delay(100);
              }

Serial Monitor - Light and dark

Test with three sensors: left - center - right

Connections at Xiao ESP 32 C3 using the protoboard

// Using three TCRT5000L reflective optical sensor
            // Input devices 
            // Board: Seeed Studio XIAO ESP 32 C3

              #define sensor1 D6   // cambia al GPIO/pin que uses
              #define sensor2 D5   // cambia al GPIO/pin que uses
              #define sensor3 D4   // cambia al GPIO/pin que uses

              void setup() {
                  Serial.begin(115200);
                  pinMode(sensor1, INPUT);  
                  pinMode(sensor2, INPUT);  
                  pinMode(sensor3, INPUT);  
              }

              void loop() {
                  int val1 = digitalRead(sensor1);
                  int val2 = digitalRead(sensor2);
                  int val3 = digitalRead(sensor3);
            
              if(val1==1){
                  Serial.println("izquierda");
                  }
              else if(val2==1){
                  Serial.println("centro");
               }
              else if(val3==1){
                   Serial.println("derecha");
              }
              else{
                    Serial.println("error");
              }
              delay(100);
              }

Testing devices

Using three TCRT5000L reflective optical sensor & buzzer - Center or not

// Using three TCRT5000L reflective optical sensor & buzzer - Center or not
              // Input devices 
              // Board: Seeed Studio XIAO ESP 32 C3

              #define sensor1 D6   // cambia al GPIO/pin que uses
              #define sensor2 D5   // cambia al GPIO/pin que uses
              #define sensor3 D4   // cambia al GPIO/pin que uses


              void setup() {
                  Serial.begin(115200);
                  pinMode(sensor1, INPUT);  
                  pinMode(sensor2, INPUT);  
                  pinMode(sensor3, INPUT);  
                  pinMode(D3, OUTPUT);
              }

              void loop() {
                int val1 = digitalRead(sensor1);
                int val2 = digitalRead(sensor2);
                int val3 = digitalRead(sensor3);
                if(val1==1){
                  Serial.println("izquierda");
                    digitalWrite (D3, HIGH);
                    delayMicroseconds (5000);
                    digitalWrite (D3, LOW);
                    delayMicroseconds (100000);
                }
                else if(val2==1){
                  Serial.println("centro");
                }
                else if(val3==1){
                  Serial.println("derecha");
                    digitalWrite (D3, HIGH);
                    delayMicroseconds (5000);
                    digitalWrite (D3, LOW);
                    delayMicroseconds (100000);
                }
                else{
                  Serial.println("error");
                    digitalWrite (D3, HIGH);
                    delayMicroseconds (5000);
                    digitalWrite (D3, LOW);
                    delayMicroseconds (100000);
                }
                delay(100);
              }

4.1) Additional individual assigment

Details

Designed microcontroller board read real

Showed output - serial monitor valuess

Included code

Demostrate that its works

We repeated the demonstration in Week 10. Input/Output devices were connected.

We repeated one process using the Xiao ESP32 C3, HC-SR04 (distance device) and a 1.3" OLED IIC. An Input and output devices were connected. The screenshot shows the verify and upload process.

Arduino One screenshot - Verify

Serial Monitor with distance detected by the HC-SR04 sensor

Input/Output devices connected using HC-SR04 sensor and OLEC IIC

Whole devices and the designed PCB


                    ESP32-C3 (Xiao) + HC-SR04 Ultrasonic + 1.3" OLED I2C
                    -------------------------------------------------------
                    Board   : Seeed Studio XIAO ESP32-C3
                    Sensor  : HC-SR04 Ultrasonic Distance Sensor
                    Display : 1.3" OLED SH1106 I2C

                    HC-SR04 Wiring:
                      HC-SR04 VCC  → 5V
                      HC-SR04 GND  → GND
                      HC-SR04 TRIG → D3 (GPIO3)
                      HC-SR04 ECHO → D2 (GPIO2)  via voltage divider (see below!)

                    !! HC-SR04 ECHO outputs 5V — ESP32-C3 is NOT 5V tolerant !!
                    !! Use a voltage divider on ECHO pin:                       !!
                    !!   ECHO → 1kΩ → D2 (GPIO2)                               !!
                    !!                       └── 2kΩ → GND                     !!

                    OLED I2C Wiring:
                      OLED VCC → 3.3V
                      OLED GND → GND
                      OLED SDA → D4 (GPIO4)
                      OLED SCL → D5 (GPIO5)

                    Libraries needed:
                      - U8g2  by oliver
                  */

                  #include 
                  #include 

                  // ── Pin config ────────────────────────────────────────────────────────────────
                  #define TRIG_PIN  D3    // D3 / GPIO3
                  #define ECHO_PIN  D2    // D2 / GPIO2 (via voltage divider)

                  #define MAX_DISTANCE_CM  400   // HC-SR04 max reliable range

                  // ── Objects ───────────────────────────────────────────────────────────────────
                  U8G2_SH1106_128X64_NONAME_F_HW_I2C u8g2(U8G2_R0, U8X8_PIN_NONE);

                  // ── Helper: measure distance ───────────────────────────────────────────────────
                  float measureDistanceCM() {
                    // Send 10us trigger pulse
                    digitalWrite(TRIG_PIN, LOW);
                    delayMicroseconds(2);
                    digitalWrite(TRIG_PIN, HIGH);
                    delayMicroseconds(10);
                    digitalWrite(TRIG_PIN, LOW);

                    // Measure echo pulse duration (timeout = max range in us)
                    long duration = pulseIn(ECHO_PIN, HIGH, 30000);

                    if (duration == 0) return -1;  // No echo = out of range

                    float distanceCM = (duration * 0.0343) / 2.0;

                    if (distanceCM > MAX_DISTANCE_CM) return -1;
                    return distanceCM;
                  }

                  // ── Setup ─────────────────────────────────────────────────────────────────────
                  void setup() {
                    Serial.begin(115200);
                    while (!Serial) delay(10);

                    pinMode(TRIG_PIN, OUTPUT);
                    pinMode(ECHO_PIN, INPUT);

                    Serial.println("=== XIAO ESP32-C3 + HC-SR04 + 1.3 OLED ===");

                    u8g2.begin();
                    u8g2.clearBuffer();
                    u8g2.setFont(u8g2_font_ncenB08_tr);
                    u8g2.drawStr(10, 30, "Initialising...");
                    u8g2.sendBuffer();

                    delay(500);
                  }

                  // ── Main Loop ─────────────────────────────────────────────────────────────────
                  void loop() {
                    float distCM = measureDistanceCM();
                    float distIN = distCM / 2.54;

                    // ── Serial output ──
                    if (distCM < 0) {
                      Serial.println("Distance : out of range");
                    } else {
                      Serial.print("Distance : ");
                      Serial.print(distCM, 1);
                      Serial.print(" cm  /  ");
                      Serial.print(distIN, 1);
                      Serial.println(" in");
                    }

                    // ── OLED display ──
                    u8g2.clearBuffer();

                    // Title
                    u8g2.setFont(u8g2_font_ncenB08_tr);
                    u8g2.drawStr(18, 12, "HC-SR04 Distance Fab");
                    u8g2.drawHLine(0, 15, 128);

                    if (distCM < 0) {
                      u8g2.setFont(u8g2_font_ncenB12_tr);
                      u8g2.drawStr(10, 42, "Out of range");
                    } else {
                      char lineCM[20], lineIN[20];
                      snprintf(lineCM, sizeof(lineCM), "%.1f cm", distCM);
                      snprintf(lineIN, sizeof(lineIN), "%.1f in", distIN);

                      u8g2.setFont(u8g2_font_ncenB18_tr);   // big font for cm
                      u8g2.drawStr(0, 42, lineCM);

                      u8g2.setFont(u8g2_font_ncenB12_tr);   // smaller for inches
                      u8g2.drawStr(0, 62, lineIN);
                    }

                    u8g2.sendBuffer();

                    delay(200);  // update 5x per second for smooth readings
                  }

Video demonstration

4.2) Additional individual assignment 2

Details

Use your own PCB, show: schematic, working with sensor

Add mesasure reading - voltaje value

Explain analog & digital signals

Add circuit diagram

My designed PCB in different versions

Schematic PCB on Fusion

Schematic PCB with measures and tolerances

Measure reading with Sharp sensor - output on serial monitor. Sensor details at: https://naylampmechatronics.com/blog/55_tutorial-sensor-de-distancia-sharp.html

Multimeter reading - voltages values

Oscilloscope reading - digital signal using HC-SR04

Oscilloscope reading - analog signal using Sharp

Difference between analog and digital signals. Analog is continuous and in this example could take any value between - 5v to 5v. Digital is discrete, generating square waves and values of 0 and 1