9. Input
devices

Programming

Once the hardware was connected, I programmed the XIAO RP2350 using Arduino IDE to read the live acceleration values from the MPU6050. The first step was to connect the PCB to Arduino IDE.

CONNECTION PROCESS:

1. Open Arduino IDE and go to File > Preferences.

2. In Additional Boards Manager URLs, paste this link: https://github.com/earlephilhower/arduino-pico/releases/download/global/package_rp2040_index.json

3. Go to Tools > Board > Boards Manager.

4. Search for Raspberry Pi Pico / RP2040 / RP2350 package and install it.

5. Once installed, select: Tools > Board > Raspberry Pi RP2350 Boards > Seeed XIAO RP2350.

6. Connect the XIAO board to the computer using USB-C.

7. Press and hold the BOOT button. Press and release the RESET button. Release the BOOT button so the board enters upload mode.

← →

Since I am not very good at programming jet I used Gemini to develop the code. This was the prompt:
Act as an expert electronics teacher and Arduino programmer. I am a beginner learning electronics and I want to write a code for the MPU6050 on pins D4 (SDA) and D5 (SCL). I want to do this completely from scratch, without using the Wire library, just controlling the pins directly. I need the code to calculate the movement velocity. To do this, please remove the normal gravity so it only detects when I actually move it. If I leave it still on the table, the velocity should slowly drop back to zero. Finally, I want to watch the data on the Serial Plotter. Please multiply the results by 50 so the waves look bigger on the screen, and add a constant zero line as a reference. Since you are an expert teacher, please add clear comments to the code and explain how the manual pin control (bit-banging) works in simple terms.

Instead of using a standard external library, I used a custom code that manually creates the I2C communication through bit-banging. This means the code itself controls the SDA and SCL pulses to talk directly to the sensor.

Final result of the code:
Every time I moved the sensor, the X, Y, and Z values changed live on screen, which confirmed that the input device was working correctly.

SOURCE CODE:

#define SCL_PIN D5
#define SDA_PIN D4
#define MPU_ADDR 0x68
 
// VARIABLES DE TIEMPO Y VELOCIDAD
unsigned long lastTime = 0;
float velocidad = 0.0;
 
// --- I2C BIT-BANGING FUNCTIONS ---
void i2c_start() {
  pinMode(SDA_PIN, OUTPUT);
  digitalWrite(SDA_PIN, HIGH); digitalWrite(SCL_PIN, HIGH);
  delayMicroseconds(5);
  digitalWrite(SDA_PIN, LOW); delayMicroseconds(5);
  digitalWrite(SCL_PIN, LOW);
}
 
void i2c_stop() {
  pinMode(SDA_PIN, OUTPUT);
  digitalWrite(SDA_PIN, LOW); digitalWrite(SCL_PIN, HIGH);
  delayMicroseconds(5);
  digitalWrite(SDA_PIN, HIGH); delayMicroseconds(5);
}
 
bool i2c_write(uint8_t byte) {
  pinMode(SDA_PIN, OUTPUT);
  for (int i = 0; i < 8; i++) {
    digitalWrite(SDA_PIN, (byte & 0x80) ? HIGH : LOW);
    byte <<= 1; delayMicroseconds(5);
    digitalWrite(SCL_PIN, HIGH); delayMicroseconds(5);
    digitalWrite(SCL_PIN, LOW);
  }
  pinMode(SDA_PIN, INPUT_PULLUP);
  digitalWrite(SCL_PIN, HIGH); delayMicroseconds(5);
  bool ack = (digitalRead(SDA_PIN) == LOW);
  digitalWrite(SCL_PIN, LOW);
  return ack;
}
 
uint8_t i2c_read(bool ack) {
  uint8_t byte = 0;
  pinMode(SDA_PIN, INPUT_PULLUP);
  for (int i = 0; i < 8; i++) {
    digitalWrite(SCL_PIN, HIGH); delayMicroseconds(5);
    byte = (byte << 1) | digitalRead(SDA_PIN);
    digitalWrite(SCL_PIN, LOW); delayMicroseconds(5);
  }
  pinMode(SDA_PIN, OUTPUT);
  digitalWrite(SDA_PIN, ack ? LOW : HIGH);
  digitalWrite(SCL_PIN, HIGH); delayMicroseconds(5);
  digitalWrite(SCL_PIN, LOW);
  return byte;
}
 
void setup() {
  Serial.begin(115200);
  pinMode(SCL_PIN, OUTPUT);
  pinMode(SDA_PIN, INPUT_PULLUP);
 
  delay(3000);
 
  i2c_start();
  i2c_write(MPU_ADDR << 1);
  i2c_write(0x6B);
  i2c_write(0);    
  i2c_stop();
 
  lastTime = micros();
}
 
void loop() {
  // 1. ADQUISICIÓN DE DATOS (ACELERÓMETRO)
  i2c_start();
  i2c_write(MPU_ADDR << 1);
  i2c_write(0x3B);
  i2c_stop();
 
  i2c_start();
  i2c_write((MPU_ADDR << 1) | 1);
  int16_t ax_raw = (i2c_read(true) << 8) | i2c_read(true);
  int16_t ay_raw = (i2c_read(true) << 8) | i2c_read(true);
  int16_t az_raw = (i2c_read(true) << 8) | i2c_read(false);
  i2c_stop();
 
  // 2. CÁLCULO DEL TIEMPO (dt)
  unsigned long currentTime = micros();
  float dt = (currentTime - lastTime) / 1000000.0;
  lastTime = currentTime;
 
  // 3. CONVERSIÓN A m/s^2
  float ax = (ax_raw / 16384.0) * 9.81;
  float ay = (ay_raw / 16384.0) * 9.81;
  float az = (az_raw / 16384.0) * 9.81;
 
  // 4. AISLAR EL MOVIMIENTO PURO (Sin importar la rotación)
  // Calculamos la magnitud total y le restamos 1 Gravedad (9.81)
  float magnitudTotal = sqrt(ax*ax + ay*ay + az*az);
  float aceleracionDinamica = magnitudTotal - 9.81;
 
  // Filtro de ruido: Si el movimiento es muy leve, lo forzamos a 0
  if (abs(aceleracionDinamica) < 0.5) {
    aceleracionDinamica = 0;
    // Fricción matemática: Si está quieto, la velocidad cae a cero rápidamente
    velocidad *= 0.85;
  } else {
    // 5. INTEGRACIÓN (Aceleración -> Velocidad)
    velocidad += aceleracionDinamica * dt;
  }
 
  // 6. SERIAL PLOTTER CON "LUPA" VISUAL
  // Multiplicamos por 50 para exagerar los picos en la gráfica
  Serial.print("Base_Cero:0,"); // Línea de referencia estática
  Serial.print("Aceleracion_Amplificada:"); Serial.print(aceleracionDinamica * 50);
  Serial.print(",");
  Serial.print("Velocidad_Amplificada:"); Serial.println(velocidad * 50);
 
  delay(20);
}