raspberrypi5-motion-sensor

Python script for Raspberry Pi 5 (Ubuntu 24.04) using the GY-521 (MPU6050) over I²C.
The script performs automatic calibration at startup and then continuously outputs:

• Accelerations (m/s²) in the three axes
• Integrated velocities (m/s)

in a two-line layout:

X(Forward/Backward): +0.45 m/s² | Y(Left/Right): +0.59 m/s² | Z(Up/Down): -10.76 m/s²
X(Forward/Backward): +0.12 m/s  | Y(Left/Right): +0.05 m/s  | Z(Up/Down): -0.01 m/s

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Table of Contents

• Requirements
• Wiring
• Prepare Ubuntu 24.04
• Clone Repository
• Installation
• Run & Usage
• How Calibration Works
• Drift Reduction Tips
• Troubleshooting
• FAQ

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Requirements

• Raspberry Pi 5 running Ubuntu 24.04
• GY-521 (MPU-6050 breakout board)
• Jumper cables (M–F)
• Python 3

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Wiring

GY-521 → Raspberry Pi 5 GPIO header:

GY-521 Pin	Raspberry Pi 5	Note
VCC	5V	Board includes regulator & level shifters → 5V safe
GND	GND	Common ground
SDA	GPIO 2 (SDA1)	I²C data
SCL	GPIO 3 (SCL1)	I²C clock
AD0	(floating/LOW)	Address 0x68; HIGH → 0x69

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Prepare Ubuntu 24.04

1) Enable I²C

sudo apt update
sudo apt install -y raspi-config
sudo raspi-config

• Go to Interface Options → I2C → Enable
• Reboot if prompted

2) Add user to I²C group

sudo adduser $USER i2c
# log out/in or reboot

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Clone Repository

cd ~
git clone https://github.com/NEX108/raspberrypi5-motion-sensor.git
cd raspberrypi5-motion-sensor

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Installation

Ubuntu 24.04 protects system Python (PEP 668). Use APT packages (recommended) or a virtual environment.

Option A — System-wide (recommended)

sudo apt update
sudo apt install -y python3-smbus python3-smbus2 i2c-tools

Option B — Virtual Environment

sudo apt install -y python3-venv i2c-tools
python3 -m venv .venv
source .venv/bin/activate
pip install smbus2

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Run & Usage

1. Check I²C device:

i2cdetect -y 1

Expected: 0x68 (or 0x69 if AD0 is HIGH).

2. Run script (auto-calibration + measurement):

python3 accel_velocity_autocal.py

• Place the sensor/car still for ~2 seconds at startup (for calibration & gravity detection).
• Then it will continuously output two lines per cycle:
  • Line 1: Accelerations (m/s²)
  • Line 2: Velocities (m/s)

Files created:

• accel_velocity_autocal.py – main script
• mpu6050_offsets.json – calibration file

Stop with Ctrl+C.

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How Calibration Works

• Collects ~250 samples while still.
• Offsets chosen so that X≈0 g, Y≈0 g, Z≈±1 g.
• Detects gravity direction (±Z) and subtracts g accordingly.
• Saves offsets to mpu6050_offsets.json.

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Drift Reduction Tips

• Pure accelerometer integration → drift is inevitable.
• Mitigation:
  • Add deadbands (ignore tiny noise).
  • Use zero-velocity updates (reset velocity when clearly at rest).
• Better results:
  • Use IMU fusion (Madgwick/Mahony) for orientation + gravity compensation.
  • Combine with encoders or GPS.

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Troubleshooting

“Remote I/O error (121)”

• Check wiring (VCC, GND, SDA=GPIO2, SCL=GPIO3).
• Verify with i2cdetect -y 1.
• Reload I²C driver:

  sudo modprobe -r i2c_bcm2835
  sudo modprobe i2c_bcm2835

• Power-cycle sensor.

i2cdetect shows nothing

• Ensure I²C is enabled in raspi-config.
• Check soldering/wires.

Wrong address

• AD0=HIGH → 0x69. Script automatically checks 0x68/0x69.

Velocities drift away

• Normal for raw integration. Use resets or fusion.

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FAQ

Units printed?

• Line 1: Accelerations (m/s²)
• Line 2: Velocities (m/s)

VCC 5V or 3.3V?

• Use 5V (GY-521 includes regulator & level shifting).

Scaling factor?

• ±2 g → 16,384 LSB/g, 1 g ≈ 9.81 m/s².

Recalibration?

• Delete mpu6050_offsets.json and restart script.