co-test

lab4-grove-joystick

2 min read

Source: L4 — External GPIO Devices Using the Grove Base Hat

Overview

Lab 4 uses the Grove Base Hat to read a joystick (analog X/Y + digital button) and control the mouse via ydotool.

Prerequisites

  1. ydotool installed and ydotoold daemon running — see ydotool source
  2. I2C interface enabled — see enable-i2c source
  3. Grove Base Hat ribbon cable connected correctly (red line aligned with green button / PWM port)

Verify I2C after enabling

i2cdetect -y 1
# Should show UU at addresses 0x1a, 0x2a, 0x39, 0x46 (or similar)

Hardware: Joystick Wiring

Joystick has 5 pins:

PinMeaningConnect to
GNDGround (0V)GND on Grove Hat
Vcc / +5VPower (3.3V from Grove Hat)Vcc on Grove Hat
VRx / XoutAnalog X-position voltageAnalog port A0
VRy / YoutAnalog Y-position voltageAnalog port A1
SW / SelDigital button press (on/off)Digital port D22 (or any digital port)

The Grove Base Hat analog ports use channels:

  • A0 → channel 0
  • A1 → channel 1
  • A2 → channel 2, A3 → channel 3 (up to A7 → channel 7)

Code Pattern

from grove.adc import ADC
from gpiozero import Button
import subprocess
 
adc = ADC()
joystick_btn = Button(22)   # BCM pin for digital port D22
 
joystick_btn.when_pressed = lambda: subprocess.run(['ydotool', 'click', '0xC0'])
 
if __name__ == "__main__":
    from signal import pause
 
    while True:
        x_mv = adc.read_voltage(0)   # A0 → VRx
        y_mv = adc.read_voltage(1)   # A1 → VRy
 
        # Center is ~1650mV (half of 3300mV supply)
        # Map to mouse delta: positive = right/down, negative = left/up
        dx = (x_mv - 1650) // 100
        dy = (y_mv - 1650) // 100
 
        if abs(dx) > 2 or abs(dy) > 2:   # deadzone
            subprocess.run(['ydotool', 'mousemove', '-x', str(dx), '-y', str(dy)])

Signal Types

  • Joystick X/Y axes = analog signal (infinitely many positions) → read with grove.adc
  • Joystick button press = digital signal (on/off) → read with gpiozero.Button
  • Grove Base Hat converts analog → 12-bit digital → Pi reads over I2C

install requirements

# In lab-4 venv
pip install -r requirements.txt   # includes grove.py, gpiozero, lgpio

Troubleshooting: EDGE DETECTION error

sudo apt install swig liblgpio-dev build-essential
sudo apt install python3-lgpio

Add lgpio to requirements.txt and re-run pip install -r requirements.txt.

See Also

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