Week 09

Personal and Group Assignment

This week’s personal assignment was to design a circuit, run a simulation and design the PCB, while document the process.

Group Assignment

Here’s the link to our group assignment of this week.

Introduction

What are input devices?

Input devices are sensors or modules that capture information from the physical world and convert it into digital or analog signals that a microcontroller can read and process. They are the "senses" of any embedded system — without inputs, a microcontroller cannot react to its environment.

Examples of input devices include buttons, potentiometers, temperature sensors, light sensors, cameras, microphones, and inertial measurement units (IMUs) like the MPU-6050 used this week. The key challenge when working with inputs is understanding the data format, the reading protocol, and how to interpret raw values into meaningful physical quantities.

Why the MPU-6050?

The MPU-6050 is one of the most widely used IMUs in the maker and engineering community. It packs a 3-axis accelerometer and a 3-axis gyroscope into a single tiny chip, communicates over I²C (only 2 wires for data), and has excellent library support for Arduino. It's the perfect sensor to explore digital communication protocols, multi-axis data reading, and physical motion interpretation — all in one device.

The Sensor

MPU-6050 Overview

The MPU-6050 is a 6-DOF Inertial Measurement Unit manufactured by InvenSense (now TDK). It integrates a 3-axis MEMS accelerometer and a 3-axis MEMS gyroscope on the same silicon die, along with an onboard Digital Motion Processor (DMP) capable of running sensor fusion algorithms directly on the chip — offloading that computation from the main microcontroller.

The accelerometer measures linear acceleration (including gravity), while the gyroscope measures angular velocity. Used together with filtering techniques, they allow accurate estimation of orientation and motion in 3D space.

Technical Specifications

Parameter	Value
Manufacturer	InvenSense (TDK)
Operating Voltage	2.375 – 3.46V (breakout module: 3.3V – 5V)
Current Consumption	3.9 mA (active) / 5 μA (sleep mode)
Accelerometer Range	±2g / ±4g / ±8g / ±16g (configurable)
Gyroscope Range	±250 / ±500 / ±1000 / ±2000 °/s (configurable)
ADC Resolution	16-bit per axis
Communication Protocol	I²C (up to 400 kHz) / SPI
I²C Address	0x68 (AD0 = LOW) / 0x69 (AD0 = HIGH)
Onboard DMP	Yes — quaternion output, gesture detection
Operating Temperature	–40°C to +85°C
Module Dimensions	20.3 × 15.6 mm

Pinout

VCC

Module power supply

3.3V – 5V

GND

Ground / reference

SDA

I²C data line

XIAO D4

SCL

I²C clock line

XIAO D5

AD0

I²C address select

LOW = 0x68

INT

Interrupt output

Optional

XDA / XCL

Auxiliary I²C bus

Optional

Wiring

Connecting MPU-6050 to XIAO RP2350

The MPU-6050 uses the I²C protocol, which requires only two data lines: SDA (data) and SCL (clock). On the Seeed XIAO RP2350, the dedicated I²C pins are D4 (SDA) and D5 (SCL), mapped to GPIO 6 and GPIO 7. The module is powered from the 3.3V pin — no level shifting needed since the XIAO RP2350 is a 3.3V device.

When AD0 is connected to GND, the I²C address is 0x68. Connecting it to 3.3V changes the address to 0x69, allowing two MPU-6050 modules on the same I²C bus simultaneously.

Connection Diagram

MPU-6050 Pin	XIAO RP2350 Pin	Note
VCC	3.3V	XIAO is 3.3V — no regulator needed
GND	GND	Common ground
SDA	D4 (GPIO 6)	I²C data line
SCL	D5 (GPIO 7)	I²C clock line
AD0	GND	Sets I²C address to 0x68
INT	Not connected	Optional interrupt output

Important Note

The XIAO RP2350 operates at 3.3V logic — this is a perfect match for the MPU-6050, which also runs at 3.3V natively. No level shifting or onboard regulator is needed. Connect VCC directly to the XIAO's 3.3V pin. Avoid connecting to the 5V (VBUS) pin as it could damage the sensor.

Code

Library Setup

To interface the MPU-6050 with the XIAO RP2350 using the Arduino framework, I used the MPU6050 library by Electronic Cats (based on Jeff Rowberg's original work), along with the built-in Wire.h for I²C communication. The XIAO RP2350 is fully compatible with Arduino IDE using the Raspberry Pi Pico board package.

1In Arduino IDE → Preferences → add https://github.com/earlephilhower/arduino-pico/releases/download/global/package_rp2040_index.json to Board Manager URLs
2Install "Raspberry Pi Pico/RP2040" board package and select Seeed XIAO RP2350
3Search for "MPU6050" by Electronic Cats in Library Manager and click Install
4Also install the dependency "I2Cdev" if prompted
5Verify: File → Examples → MPU6050 → MPU6050_raw

Accelerometer & Gyroscope

// week10_mpu6050_basic.ino — XIAO RP2350

#include <Wire.h>
#include <MPU6050.h>
 
MPU6050 mpu;
 
void setup() {
  Serial.begin(115200);
  Wire.begin();           // Initialize I²C — uses D4/D5 on XIAO RP2350
  mpu.initialize();       // Wake up the MPU-6050
 
  if (mpu.testConnection()) {
    Serial.println("MPU-6050 connected!");
  } else {
    Serial.println("Connection failed. Check wiring.");
  }
 
  // Set accelerometer range: ±2g
  mpu.setFullScaleAccelRange(MPU6050_ACCEL_FS_2);
  // Set gyroscope range: ±250 deg/s
  mpu.setFullScaleGyroRange(MPU6050_GYRO_FS_250);
}
 
void loop() {
  int16_t ax, ay, az;
  int16_t gx, gy, gz;
 
  // Read all 6 axes in one call
  mpu.getMotion6(&ax, &ay, &az, &gx, &gy, &gz);
 
  // Convert raw values to real units
  // Accel sensitivity at ±2g = 16384 LSB/g
  float accel_x = ax / 16384.0;
  float accel_y = ay / 16384.0;
  float accel_z = az / 16384.0;
 
  // Gyro sensitivity at ±250 deg/s = 131 LSB/deg/s
  float gyro_x = gx / 131.0;
  float gyro_y = gy / 131.0;
  float gyro_z = gz / 131.0;
 
  Serial.print("Accel (g)  X:"); Serial.print(accel_x);
  Serial.print("  Y:");       Serial.print(accel_y);
  Serial.print("  Z:");       Serial.println(accel_z);
 
  Serial.print("Gyro(d/s)  X:"); Serial.print(gyro_x);
  Serial.print("  Y:");         Serial.print(gyro_y);
  Serial.print("  Z:");         Serial.println(gyro_z);
 
  Serial.println("---");
  delay(200);
}

Results

Observed Behavior

After uploading the code and opening the Serial Monitor, the MPU-6050 responded immediately with readings. When the sensor was flat on the desk, the Z-axis of the accelerometer read approximately 1g due to Earth's gravity, while X and Y remained close to zero. Tilting the module caused the gravity vector to distribute across the axes — which is exactly the principle behind tilt sensing.

The gyroscope produced values close to zero when stationary (with a small amount of noise, called gyro drift). Significant values only appeared during active rotation. This confirmed that the gyroscope measures angular velocity, not position — and integrating over time to get angle accumulates error.

Z-axis at rest (accel)

~1.0g

Accel sensitivity (±2g)

16384LSB/g

Gyro sensitivity (±250°/s)

131LSB/°/s

Sampling rate (tested)

~100Hz

Accelerometer vs Gyroscope

The accelerometer is well-suited for measuring static tilt angles because gravity provides a stable reference — but it's sensitive to vibrations and sudden shocks, which produce noisy readings.

The gyroscope delivers smooth, low-noise angular velocity data during motion, but its readings drift over time when integrated to compute angle — errors accumulate. The industry-standard solution (used in phones, drones, and game controllers) combines both sensors through a complementary filter or Kalman filter, achieving stable and accurate orientation estimates.

Input Devices