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I am basically trying to turn on a led by using pi4j library. My code is pretty simple:

public static void main(String args[]) throws InterruptedException {
    GpioController gpioController = GpioFactory.getInstance();
    GpioPinDigitalOutput pinOut = gpioController.provisionDigitalOutputPin(RaspiPin.GPIO_17);
    pinOut.high();
    Thread.sleep(5000);
    pinOut.low();
}

I am exporting the jar file from my computer, copying to my Raspberry Pi 4 than running in there.

To check if my led is not broken or GPIO is set, I've executed following Python scripts and I see my led works perfectly:

python
import RPi.GPIO as GPIO
GPIO.setmode(GPIO.BCM)
GPIO.setup(17, GPIO.OUT)
GPIO.output(17,True)

What am I missing?

osumatu
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    Do you get any errors? My concern is that Pi 4 is not supported going by the list at https://pi4j.com/1.2/ Also check that the pin numbering https://pi4j.com/1.2/pin-numbering-scheme.html matches the BCM numbering. –  Oct 11 '20 at 16:32
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    @Andyroo I don't get any errors, I can even see the console writes on my pi. I also couldn't find anything regarding to pi4 on pi4j documentation but I didn't worry a lot since it didn't give me any errors... – osumatu Oct 11 '20 at 16:37
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    As @andyroo has said. 1) the Pi4 is not supported. 2) you are using the wrong GPIO numbering scheme. – joan Oct 11 '20 at 16:51
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    The Pi4 has GPIO located at different addresses and pull-ups are different, so the library will need to be modified. – Milliways Oct 11 '20 at 21:45
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    Or you can try BlueJ, or what Pi Mag suggests. More details in the following Q&A (Appendix B of my answer) : https://raspberrypi.stackexchange.com/questions/111679/getting-a-nrf24l01-module-running-with-java. Cheers. – tlfong01 Oct 12 '20 at 00:26

2 Answers2

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Indeed as mentioned in the comments, Pi4J is using a different pin numbering scheme. "Under the hood", WiringPi is used to control the GPIOs. This library uses a different numbering scheme. This means BCM pin 17 you are using in Python is pin 0 in the WiringPi scheme.

See below a full table with BCM, WiringPi, and physical pin numbering (see link 2 below).

Raspberry Pi numbering scheme with BCM and WiringPi numbering

Next to that, the internal wiring of the Raspberry Pi 4 is different compared to the previous ones, so you'll need to upgrade your WiringPi to the latest version 2.52 with:

$ gpio -v
gpio version: 2.50

$ cd /tmp
$ wget https://project-downloads.drogon.net/wiringpi-latest.deb
$ sudo dpkg -i wiringpi-latest.deb
$ gpio -v
gpio version: 2.52

As a side note: we are working on a new version of Pi4J which will make things easiers, but work-in-progress... ;-)

More info in my blog posts on:

  1. Using Pi4j (V1) on the Raspberry Pi 4
  2. Raspberry Pi history, versions, pins and headers as a Java Maven library
  3. Oracle Java Magazine: Getting started with JavaFX on Raspberry Pi
Frank
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  • I see there is a difference in pin numbering but when I change my code for GPIO_00 (Which is the WiringPI pin for GPIO_17) I get runtime error saying: Unable to open GPIO direction interface for pin[0]: No such file or directory. – osumatu Oct 15 '20 at 10:18
  • Just an idea, can you try another pin? E.g. pin 40 = BCM 21 = WiringPi 29 as used in the example at https://blogs.oracle.com/javamagazine/getting-started-with-javafx-on-raspberry-pi#anchor_5 – Frank Oct 15 '20 at 17:40
  • Yes indeed, for some reason some pins are working and some are not. I am basically just brute-forcing to see which ones I can use. Thanks for the reply. – osumatu Nov 01 '20 at 11:29
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Since I don't have enough reputation to comment...

In the PI4J library, you use constants like "GPIO_16"... However, these are not the GPIO pins that you find in the RPI documentation. They are the WiringPI pins.

A mapping is here: https://pinout.xyz/pinout/wiringpi

winrid
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