Raspberry Pi Build HAT: Complete Python Guide to LEGO Motor Control

Table of Contents

• Hardware Overview
• Installation & Setup
• Motor Control
• Sensor Reading
• Advanced: NumPy & OpenCV Integration
• Project Ideas

Hardware Overview

The Build HAT solves the biggest challenge in Pi + LEGO integration: power and voltage management.

Key Specifications

Compatible LEGO Devices

• Motors: Technic Large/XL, SPIKE Prime Medium/Large, MINDSTORMS motors
• Sensors: Color sensor, Distance sensor, Force sensor
• Not Compatible: Powered Up hub (it IS a hub), Power Functions (different connector)

Installation & Setup

Hardware Setup

1. Power off your Raspberry Pi
2. Align the Build HAT with the 40-pin GPIO header
3. Press down firmly until fully seated
4. Connect 8V power supply to the barrel jack
5. Connect motors/sensors to the LPF2 ports (A, B, C, D)

Software Installation

# Update your Pi
sudo apt update && sudo apt upgrade -y

# Enable serial port (required for Build HAT communication)
sudo raspi-config nonint do_serial 2  # Enable serial, disable console

# Install the Build HAT Python library
pip3 install buildhat

# Verify installation
python3 -c "from buildhat import Hat; hat = Hat(); print(f'Build HAT firmware: {hat.get_firmware()}')"

# Reboot to apply serial changes
sudo reboot

Motor Control

Basic Motor Operations

from buildhat import Motor

# Initialize motor on port A
motor = Motor('A')

# Run at speed (degrees per second)
motor.run_for_seconds(2, speed=50)  # Run for 2 seconds at 50% speed

# Run for specific rotations
motor.run_for_rotations(3, speed=75)  # 3 full rotations at 75%

# Run to absolute position
motor.run_to_position(180, speed=50)  # Move to 180 degrees

# Get current position
position = motor.get_position()
print(f"Motor position: {position} degrees")

Motor Pair for Drive Systems

from buildhat import MotorPair

# Initialize paired motors for tank drive
motors = MotorPair('A', 'B')

# Move forward
motors.run_for_seconds(2, speedl=50, speedr=50)

# Turn left (right motor faster)
motors.run_for_seconds(1, speedl=20, speedr=50)

# Spin in place
motors.run_for_seconds(1, speedl=50, speedr=-50)

Precise Position Control

from buildhat import Motor
import time

motor = Motor('A')

# Enable position tracking
motor.set_default_speed(30)

# Move to specific angles
for angle in [0, 90, 180, 270, 360]:
    motor.run_to_position(angle)
    print(f"Moved to {angle}°")
    time.sleep(0.5)

Sensor Reading

Color Sensor

from buildhat import ColorSensor

sensor = ColorSensor('C')

# Get detected color name
color = sensor.get_color()
print(f"Detected: {color}")  # 'red', 'blue', 'green', etc.

# Get RGB values
r, g, b = sensor.get_color_rgbi()[:3]
print(f"RGB: ({r}, {g}, {b})")

# Get reflected light intensity (0-100)
light = sensor.get_reflected_light()
print(f"Reflected light: {light}%")

# Get ambient light
ambient = sensor.get_ambient_light()
print(f"Ambient light: {ambient}%")

Distance Sensor

from buildhat import DistanceSensor

sensor = DistanceSensor('D')

# Get distance in centimeters
distance = sensor.get_distance()
print(f"Distance: {distance} cm")

# Continuous monitoring
while True:
    d = sensor.get_distance()
    if d and d < 10:
        print("Object detected nearby!")
    time.sleep(0.1)

Force Sensor

from buildhat import ForceSensor

sensor = ForceSensor('B')

# Get force in Newtons (0-10N)
force = sensor.get_force()
print(f"Force: {force}N")

# Check if pressed
if sensor.is_pressed():
    print("Button pressed!")

Advanced: NumPy & OpenCV Integration

The Build HAT's Python library opens the door to the entire Python ecosystem. Here's where things get powerful.

Data Logging with Pandas

from buildhat import Motor, ColorSensor
import pandas as pd
import time

motor = Motor('A')
sensor = ColorSensor('C')

# Collect data while motor runs
data = []
motor.start(speed=30)

for i in range(100):
    data.append({
        'time': time.time(),
        'position': motor.get_position(),
        'color': sensor.get_color(),
        'light': sensor.get_reflected_light()
    })
    time.sleep(0.1)

motor.stop()

# Create DataFrame and analyze
df = pd.DataFrame(data)
df.to_csv('motor_data.csv')
print(df.describe())

Computer Vision with OpenCV

from buildhat import Motor
import cv2
import numpy as np

# Initialize camera and motor
cap = cv2.VideoCapture(0)
sorting_motor = Motor('A')

while True:
    ret, frame = cap.read()
    if not ret:
        break

    # Convert to HSV for color detection
    hsv = cv2.cvtColor(frame, cv2.COLOR_BGR2HSV)

    # Define red color range
    lower_red = np.array([0, 100, 100])
    upper_red = np.array([10, 255, 255])
    mask = cv2.threshold(hsv, lower_red, upper_red)

    # If red detected, activate sorting gate
    if cv2.countNonZero(mask) > 1000:
        sorting_motor.run_to_position(90)  # Open gate
    else:
        sorting_motor.run_to_position(0)   # Close gate

    cv2.imshow('Frame', frame)
    if cv2.waitKey(1) & 0xFF == ord('q'):
        break

cap.release()

Scientific Computing with NumPy

from buildhat import Motor
import numpy as np

motor = Motor('A')

# Generate smooth acceleration curve using NumPy
speeds = np.linspace(0, 100, 50)  # 0 to 100 in 50 steps

# Acceleration phase
for speed in speeds:
    motor.start(speed=int(speed))
    time.sleep(0.05)

# Deceleration phase
for speed in reversed(speeds):
    motor.start(speed=int(speed))
    time.sleep(0.05)

motor.stop()

Project Ideas

1. Data-Logging Weather Station

Use external I2C sensors (temperature, humidity, pressure) with motor-actuated displays showing current conditions.

2. Automated LEGO Sorter

Combine Pi Camera + OpenCV for part identification with Build HAT motors for conveyor and sorting gates.

3. Robotic Arm with Inverse Kinematics

Use NumPy/SciPy to calculate joint angles for precise end-effector positioning.

4. Line-Following Robot

Color sensor reads track, PID algorithm (implemented in Python) controls motor speeds for smooth following.

Resources

• Build HAT Documentation
• Raspberry Pi Build HAT Product Page
• Build HAT Python Library (GitHub)