2.1.6 Joystick

Introduction

In this project, We’re going to learn how joystick works. We manipulate the Joystick and display the results on the screen.

Components

../_images/image317.png

Schematic Diagram

When the data of joystick is read, there are some differents between axis: data of X and Y axis is analog, which need to use ADC0834 to convert the analog value to digital value. Data of Z axis is digital, so you can directly use the GPIO to read, or you can also use ADC to read.

../_images/image319.png ../_images/image320.png

Experimental Procedures

Step 1: Build the circuit.

../_images/image193.png

Step 2: Go to the folder of the code.

cd /home/pi/davinci-kit-for-raspberry-pi/nodejs/

Step 3: Run the code.

sudo node joystick.js

After the code runs, turn the Joystick, then the corresponding values of x, y, Btn are displayed on screen.

Code

const Gpio = require('pigpio').Gpio;
const ADC0834 = require('./adc0834.js').ADC0834;

const adc = new ADC0834(17, 18, 22);
const btn = new Gpio(25, {
    mode: Gpio.INPUT,
    pullUpDown: Gpio.PUD_UP,
});

setInterval(async() => {

    x_val = await adc.read(0);
    y_val = await adc.read(1);

    btn_val = btn.digitalRead();
    console.log(`x = ${x_val}, y = ${y_val}, btn = ${btn_val}\n`);
}, 100);

Code Explanation

const ADC0834 = require('./adc0834.js').ADC0834;

We import an ADC0834 constructor to use the adc0834 module.

setInterval(async() => {

    x_val = await adc.read(0);
    y_val = await adc.read(1);

    btn_val = btn.digitalRead();
    console.log(`x = ${x_val}, y = ${y_val}, btn = ${btn_val}\n`);
}, 100);

When reading the values of multiple channels of ADC0834 at the same time, asynchronous programming is required. We build a promise function here, And use the await instruction of async function to elegantly write this complex asynchronous task.

Phenomenon Picture

../_images/image194.jpeg