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2.11 Joystick

Introduction

A joystick is an input device commonly used for gaming, robotics, and navigation systems. It typically has two axes (X and Y) for directional control and a button (Btn or SW) for additional input. In this project, you will learn how a joystick works by manipulating it and displaying the corresponding values of the X, Y, and button states on the screen.

What You’ll Need

Below are the components required for this project:

COMPONENT INTRODUCTION	PURCHASE LINK
Joystick Module	-
Jumper Wires	BUY
Fusion HAT+	-
Raspberry Pi	-

Circuit Diagram

Wiring Diagram

Build the circuit as shown in the diagram below:

Ensure that:

The VRX and VRY pins of the joystick are connected to ADC pins.
The SW pin of the joystick is connected to a GPIO pin 17.
Power and ground connections are correctly set.

Running the Example

All example code used in this tutorial is available in the ai-lab-kit directory. Follow these steps to run the example:

cd ~/ai-lab-kit/python/
sudo python3 2.11_Joystick.py

This Python script read and display real-time joystick data on a Fusion HAT+. When executed:

The script continuously reads the X and Y values from the Fusion HAT+.
It monitors the button connected to GPIO pin 17 to detect whether it is pressed or not.
The X, Y, and button state values are printed to the console in the format X: <value> Y: <value> Btn: <value>, where:
- X and Y are the analog readings from the ADC chip.
- Btn is 1 when the button is not pressed and 0 when it is pressed.
The script updates every 0.2 seconds, running continuously until interrupted with Ctrl+C.

Code

Below is the Python code used for this project:

#!/usr/bin/env python3
from fusion_hat.adc import ADC
from fusion_hat.pin import Pin, Mode, Pull
import time

# Initialize the Joystick
BtnPin = Pin(17, mode=Mode.IN, pull=Pull.UP)
xAxis = ADC('A1')
yAxis = ADC('A0')

def MAP(x, in_min, in_max, out_min, out_max):
   return (x - in_min) * (out_max - out_min) / (in_max - in_min) + out_min

try:
   # Main loop to read and print ADC values and button state
   while True:
      # Read X and Y values from ADC channels
      x_val = MAP(xAxis.read(),0,4095,-100,100)
      y_val = MAP(yAxis.read(),0,4095,-100,100)

      # Read the state of the button (pressed or not)
      Btn_val = BtnPin.value()

      # Print the X, Y, and button values
      print('X: %d  Y: %d  Btn: %d' % (x_val, y_val, Btn_val))

      # Delay of 0.2 seconds before the next read
      time.sleep(0.2)

# Gracefully handle script termination (e.g., via KeyboardInterrupt)
except KeyboardInterrupt:
   pass

Understanding the Code

Imports:
```
from fusion_hat.adc import ADC
from fusion_hat.pin import Pin, Mode, Pull
import time
```
The script imports necessary modules: fusion_hat for GPIO functionalities, and time for adding delays.
Initialization:
```
# Initialize the Joystick
BtnPin = Pin(17, mode=Mode.IN, pull=Pull.UP)
xAxis = ADC('A1')
yAxis = ADC('A0')
```
The script initializes the joystick by creating instances of the Pin and ADC classes. The button is set to input mode with an internal pull-up resistor enabled, and the X and Y axes are set to read from ADC channels A0 and A1, respectively.

Main Loop:

try:
   # Main loop to read and print ADC values and button state
   while True:
      # Read X and Y values from ADC channels
      x_val = MAP(xAxis.read(),0,4095,-100,100)
      y_val = MAP(yAxis.read(),0,4095,-100,100)

      # Read the state of the button (pressed or not)
      Btn_val = BtnPin.value()

      # Print the X, Y, and button values
      print('X: %d  Y: %d  Btn: %d' % (x_val, y_val, Btn_val))

      # Delay of 0.2 seconds before the next read
      time.sleep(0.2)

# Gracefully handle script termination (e.g., via KeyboardInterrupt)
except KeyboardInterrupt:
   pass

Reads X and Y values from ADC channels 0 and 1, respectively.
Reads the button state (pressed or not) from the SW pin.
Prints the X, Y, and button values to the screen every 0.2 seconds.

Troubleshooting

ADC Values Not in Expected Range:
- Cause: Incorrect ADC channel configuration or wiring issues.
- Solution: Verify the ADC channel configuration and wiring. Ensure the joystick is connected to the correct ADC channels.
Button State Always 0:
- Cause: Incorrect button wiring or pull-up/pull-down configuration.
- Solution: Verify the button wiring. Check the pull-up/pull-down configuration to ensure the button is properly connected to the SW pin.
ADC Values Are Constant:
- Cause: The ADC channels are not connected to any input.
- Solution: Connect joysticks to ADC channels 0 and 1 to provide variable inputs.

Extendable Ideas

Joystick Control: Use the X and Y values to control a virtual joystick or game element.

Data Logging: Log the X, Y, and button values to a file for analysis:

with open("sensor_log.txt", "a") as log_file:
      log_file.write(f"X: {x_val}, Y: {y_val}, Btn: {Btn_val}\n")

Conclusion

This experiment demonstrates how to interface a joystick with a Fusion HAT+ for analog-to-digital conversion. By understanding how to read and interpret joystick inputs, you can build interactive systems for gaming, robotics, or other applications.