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4.1 Reading Values from a Joystick

In this lesson, we’ll learn how to use a joystick with the Raspberry Pi Pico 2 to read analog values and detect button presses. A joystick is a common input device that allows you to control movement along two axes (X and Y) and often includes a button when pressed down (Z-axis).

What You’ll Need

In this project, we need the following components.

It’s definitely convenient to buy a whole kit, here’s the link:

Name	ITEMS IN THIS KIT	LINK
Newton Lab Kit	450+	Newton Lab Kit

You can also buy them separately from the links below.

SN	COMPONENT	QUANTITY	LINK
1	Raspberry Pi Pico 2	1	BUY
2	Micro USB Cable	1
3	Breadboard	1	BUY
4	Jumper Wires	Several	BUY
5	Resistor	1(10KΩ)	BUY
6	Joystick Module	1

Understanding the Joystick

A typical joystick module consists of two potentiometers positioned at right angles to each other:

X-axis potentiometer: Measures left-right movement.
Y-axis potentiometer: Measures up-down movement.
Z-axis (Switch): A digital button activated when you press down on the joystick.

By reading the analog values from the X and Y axes, you can determine the position of the joystick. The Z-axis button allows you to detect when the joystick is pressed down.

Circuit Diagram

sch_joystick

The SW pin is connected to a 10K pull-up resistor, the reason is to be able to get a stable high level on the SW pin (Z axis) when the joystick is not pressed; otherwise the SW is in a suspended state and the output value may vary between 0/1.

Wiring Diagram

wiring_joystick

Writing the Code

Let’s write a MicroPython program to read the joystick’s X and Y positions and detect button presses.

Note

Open the 4.1_toggle_the_joystick.py from newton-lab-kit/micropython or copy the code into Thonny, then click “Run” or press F5.
Ensure the correct interpreter is selected: MicroPython (Raspberry Pi Pico).COMxx.

import machine
import utime

# Initialize ADC for X and Y axes
x_adc = machine.ADC(27)  # GP27
y_adc = machine.ADC(26)  # GP26

# Initialize digital input for the switch
z_button = machine.Pin(22, machine.Pin.IN, machine.Pin.PULL_UP)

while True:
    # Read the analog values (0-65535)
    x_value = x_adc.read_u16()
    y_value = y_adc.read_u16()

    # Read the button state (0 or 1)
    z_state = z_button.value()

    # Print the values
    print("X:", x_value, "Y:", y_value, "Button:", z_state)

    # Small delay to make the output readable
    utime.sleep(0.2)

Understanding the Code

Import Modules:
- machine: Provides access to hardware-related functions.
- utime: Contains time-related functions for delays.
Initialize the ADC Inputs:

We set up analog-to-digital converters (ADC) on pins GP27 and GP26 to read the joystick’s X and Y positions.
```
x_adc = machine.ADC(27)  # X-axis connected to GP27
y_adc = machine.ADC(26)  # Y-axis connected to GP26
```
Initialize the Digital Input:
- Configure GP22 as a digital input with an internal pull-up resistor for the joystick’s button (Z-axis).
- The machine.Pin.PULL_UP parameter ensures the pin reads high (1) when not pressed and low (0) when pressed.
```
z_button = machine.Pin(22, machine.Pin.IN, machine.Pin.PULL_UP)
```

Main Loop to Read Values:

Read Analog Values: read_u16() reads a 16-bit value (0 to 65535) representing the voltage level.
Print the Values: Displays the X and Y positions and the button state in the console.

while True:
    x_value = x_adc.read_u16()
    y_value = y_adc.read_u16()
    z_state = z_button.value()

    print("X:", x_value, "Y:", y_value, "Button:", z_state)

    utime.sleep(0.2)

After running the program, open the Shell or REPL window in Thonny.

You should see the X, Y, and Button values being printed.
Move the joystick in different directions and press the button to see the values change.

Interpreting the Values

X and Y Values:
- Range from 0 to 65535.
- Center Position: Around 32768.
- Full Left or Up: Close to 0.
- Full Right or Down: Close to 65535.
Button State:
- Not Pressed: 1.
- Pressed: 0.

Experimenting Further

Normalize the Values:

Convert the raw ADC values to a range of -100 to 100 for easier interpretation.

import machine
import utime

# Initialize ADC for X and Y axes
x_adc = machine.ADC(27)  # GP27
y_adc = machine.ADC(26)  # GP26

# Initialize digital input for the switch
z_button = machine.Pin(22, machine.Pin.IN, machine.Pin.PULL_UP)

# Function to normalize ADC values to a range of -100 to 100
def normalize(value):
    return int((value - 32768) / 327.68)

while True:
    # Read the analog values (0-65535)
    x_value = x_adc.read_u16()
    y_value = y_adc.read_u16()

    # Read the button state (0 or 1)
    z_state = z_button.value()

    # Normalize the values to -100 to 100
    x_normalized = normalize(x_value)
    y_normalized = normalize(y_value)

    # Print the normalized values
    print("X:", x_normalized, "Y:", y_normalized, "Button:", z_state)

    # Small delay to make the output readable
    utime.sleep(0.2)

Control an Output:

Use the joystick input to control an LED, servo, or motor. For example, move an object left or right based on the X-axis value.
Create a Game Controller:

Combine the joystick inputs to control a simple game or graphical output.

Conclusion

In this lesson, you’ve learned how to read analog and digital inputs from a joystick using the Raspberry Pi Pico 2. This knowledge allows you to incorporate joystick controls into your projects, enabling interactive applications like robots, games, or remote controls.