Chapter 2 Flowing Light

We have learned how to control one LED to blink. Next, we will learn how to control a number of LEDs.

Project Flowing Water Light

In this project, we use a number of LEDs to make a flowing water light.

Component List

Freenove Projects Board for Raspberry Pi
Raspberry Pi	GPIO Ribbon Cable

Circuit

Schematic diagram

Hardware connection:

Note

If you have any concerns, please send an email to: support@freenove.com

Sketch

In this chapter, we will introduce how to control multiple LEDs with various GPIOs, and make the LEDs present a flowing effect.

Sketch_02_FlowingLight

First, enter where the project is located:

$ cd ~/Freenove_Kit/Pi4j/Sketches/Sketch_02_FlowingLight

Enter the command to run the code.

$ jbang FlowingLight.java

When the code is running, you can see the onboard indicators lights up in a flowing effect.

On the Raspberry Pi Terminal, you can see messages printed.

Press CTRL+C to exit the code.

You can view and edit the code with Geany by running the following command.

$ geany FlowingLight.java

Click the icon to run the code.

If the code fails to run, please check Geany Configuration.

The following is program code:

///usr/bin/env jbang "$0" "$@" ; exit $?  
  
//DEPS org.slf4j:slf4j-api:2.0.12  
//DEPS org.slf4j:slf4j-simple:2.0.12  
//DEPS com.pi4j:pi4j-core:2.6.0  
//DEPS com.pi4j:pi4j-plugin-raspberrypi:2.6.0  
//DEPS com.pi4j:pi4j-plugin-gpiod:2.6.0  
  
import com.pi4j.Pi4J;  
import com.pi4j.io.gpio.digital.DigitalOutput;  
import com.pi4j.util.Console;  
  
public class FlowingLight {  
    // Define the GPIO pin number for the LED.
    private static final int[] LED_PINS = {14, 15, 18, 23, 24, 25, 8, 7, 12, 16, 20, 21};  
  
    public static void main(String[] args) throws Exception {  
        final var console = new Console();  
        var pi4j = Pi4J.newAutoContext();  
        
        DigitalOutput[] leds = new DigitalOutput[LED_PINS.length];  
        for (int i = 0; i < LED_PINS.length; i++) {  
            leds[i] = pi4j.dout().create(LED_PINS[i]);  
        }  
  
        try {  
            int currentLed = 0; 
            while (true) {  
                console.println("LED " + LED_PINS[currentLed] + " is ON");  
                for (DigitalOutput led : leds) {  
                    led.low();  
                }  
                leds[currentLed].high();  
                Thread.sleep(100);  
                currentLed = (currentLed + 1) % LED_PINS.length;  
            }  
        } finally {  
            pi4j.shutdown(); 
        }  
    }  
}

Import the classes of Pi4J library for GPIO control and simple console output.

import com.pi4j.Pi4J;  
import com.pi4j.io.gpio.digital.DigitalOutput;  
import com.pi4j.util.Console;  

Define an array that includes the GPIO numbers connecting to LEDs.

// Define the GPIO pin number for the LED.
private static final int[] LED_PINS = {14, 15, 18, 23, 24, 25, 8, 7, 12, 16, 20, 21};  

Create a DigitalOutput array based on the GPIO array that controls the LEDs, and create a DigitalOutput instance for each pin.

DigitalOutput[] leds = new DigitalOutput[LED_PINS.length];  
for (int i = 0; i < LED_PINS.length; i++) {  
    leds[i] = pi4j.dout().create(LED_PINS[i]);  
}  

Iterate through all LEDs and turn them off (set to low level).

for (DigitalOutput led : leds) {  
    led.low();  
}  

Use ‘currentLed’ to record the position of the LED that is lit, recalculate the position of the lit LED every 100 milliseconds, and print a prompt message to the console. At the same time, turn off all LEDs except the LED at the position recorded by ‘currentLed’.

int currentLed = 0; 
while (true) {  
    console.println("LED " + LED_PINS[currentLed] + " is ON");  
    for (DigitalOutput led : leds) {  
        led.low();  
    }  
    leds[currentLed].high();  
    Thread.sleep(100);  
    currentLed = (currentLed + 1) % LED_PINS.length;  
}