B4J Library [IoT] jPi4J - Raspberry Pi GPIO controller

Erel · Feb 5, 2014

Updated libraries: https://www.b4x.com/android/forum/threads/pi4j2-raspberry-pi-i-o-library.136113/#content

This is a wrapper for Pi4J library.
It allows you are control the Raspberry Pi board GPIO pins.

Using this library is quite simple. You can use it from a UI app or non-UI app.

First you should initialize a GpioController object.
The second step is to initialize one or more pins.

You can provision each pin to be an input pin or output pin. Input pins allow you to listen for state changes. Output pins allow you to set their state.

The following program initializes two pins. Pin1 is an input pin and pin2 is an output pin. Pin2 state is changed every 5 seconds with a timer:

B4X:

'Non-UI application (console application)
#Region  Project Attributes
   #CommandLineArgs:
   #MergeLibraries: true
#End Region

Sub Process_Globals
   Private controller As GpioController
   Private Pin2 As GpioPinDigitalInput
   Private Pin1 As GpioPinDigitalOutput
   Private Timer1 As Timer
End Sub

Sub AppStart (Args() As String)
   controller.Initialize
   Pin1.Initialize(1, True) 'GpioPinDigitalOutput
   Pin2.Initialize("Pin2", 2) 'GpioPinDigitalInput
   Pin2.SetPinPullResistance("PULL_DOWN")

   Log("Monitoring Pin2 state")
   Timer1.Initialize("Timer1", 5000)
   Timer1.Enabled = True
   StartMessageLoop
End Sub

Sub Timer1_Tick
   Pin1.State = Not(Pin1.State)
   Log("Switching Pin1 state. Pin1 state = " & Pin1.State)
End Sub

Sub Pin2_StateChange(State As Boolean)
   Log("Pin2 StateChange event: " & State)
End Sub

The pins scheme is available here: http://pi4j.com/usage.html

The output of this program:

B4J-Bridge is very useful when working with this board: http://www.b4x.com/android/forum/threads/remote-debugging-with-b4j-bridge.38804/
You can download it to the board with this command:

B4X:

wget https://www.b4x.com/b4j/files/b4j-bridge.jar

Then run it as root:

B4X:

sudo <path to java> -jar b4j-bridge.jar

PiFace extension

V1.00 adds support for the PiFace extension: http://www.savagehomeautomation.com/piface

See this post: http://www.b4x.com/android/forum/threads/jpi4j-raspberry-pi-gpio-controller.37493/#post-232767

Download link: www.b4x.com/b4j/files/jPi4J.zip

Michael1968 · Jul 30, 2014

Hi Eral, can I use http://pi4j.com/apidocs/com/pi4j/wiringpi/Lcd.html ?

Did you have a sample Code how to call the API?

thank you very much

best regards Michael

Erel · Aug 1, 2014

It should be simple to call this API with JavaObject.

B4X:

Dim lcd As JavaObject
lcd.InitializeStatic("com.pi4j.wiringpi.Lcd")
Dim handle as Int = lcd.RunMethod("lcdInit", Array(<all the ints go here>))
lcd.RunMethod("lcdPuts", Array(handle, "text"))

Michael1968 · Aug 14, 2014

Erel said:
It should be simple to call this API with JavaObject.

B4X:

Dim lcd As JavaObject lcd.InitializeStatic("com.pi4j.wiringpi.Lcd") Dim handle as Int = lcd.RunMethod("lcdInit", Array(<all the ints go here>)) lcd.RunMethod("lcdPuts", Array(handle, "text"))

thx Erel ....it works now

StarinschiAndrei · Aug 29, 2014

Hi Erel,
I try to reproduce your example on my rpi but there is no changes on pin2 when i press the button.Could you please tell me what's wrong ?

B4X:

'Non-UI application (console / server application)
#Region  Project Attributes
    #CommandLineArgs:
    #MergeLibraries: True
#End Region

Sub Process_Globals
Private controller As GpioController
  Private pin2 As GpioPinDigitalInput
  Private pin1 As GpioPinDigitalOutput
  Private Timer1 As Timer

End Sub

Sub AppStart (Args() As String)
    controller.Initialize
  pin1.Initialize(1, True) 'GpioPinDigitalOutput
  pin2.Initialize("Pin2", 2) 'GpioPinDigitalInput
  pin2.SetPinPullResistance("PULL_DOWN")

  Log("Monitoring Pin2 state")
  Timer1.Initialize("Timer1", 5000)
  Timer1.Enabled = True
  StartMessageLoop
End Sub
Sub Timer1_Tick
  pin1.State = Not(pin1.State)
  Log("Switching Pin1 state. Pin1 state = " & pin1.State)
End Sub

Sub Pin2_StateChange(State As Boolean)
  Log("Pin2 StateChange event: " & State)
End Sub

Toley · Aug 29, 2014

Sub Timer1_Tick
pin1.State = Not(pin1.State)Log("Switching Pin1 state. Pin1 state = " & pin1.State)End Sub

It looks like the change is on pin1

Erel · Aug 31, 2014

The timer updates pin1 state every 5 seconds.

In my tests I short-circuited pin2 to change its state.

StarinschiAndrei · Sep 1, 2014

Erel said:
The timer updates pin1 state every 5 seconds.

In my tests I short-circuited pin2 to change its state.

Thank you Erel, it was my fault. Below the right circuit

and the code :

B4X:

Sub Process_Globals
Private controller As GpioController
  Private pin2 As GpioPinDigitalInput
  Private pin1 As GpioPinDigitalOutput
  Private Timer1 As Timer
  Private ms As Long
End Sub

Sub AppStart (Args() As String)
    controller.Initialize
  pin1.Initialize(1, True) 'GpioPinDigitalOutput
  pin2.Initialize("Pin2", 2) 'GpioPinDigitalInput
  pin2.SetPinPullResistance("PULL_DOWN")
  ms =1000
  Log("Monitoring Pin2 state")
  Timer1.Initialize("Timer1", ms)
  Timer1.Enabled = True
  StartMessageLoop
End Sub
Sub Timer1_Tick
  pin1.State = Not(pin1.State)
  Log("Switching Pin1 state. Pin1 state = " & pin1.State & "Interval :" & ms )
End Sub

Sub Pin2_StateChange(State As Boolean)
If State = False Then
    If ms <9000 Then
          Log("Pin2 StateChange event: " & State)
          ms =ms+ 1000
    Else
          ms =1000
    End If   
   Timer1.Initialize("Timer1",ms)
End If
End Sub

StarinschiAndrei · Sep 1, 2014

Hi Erel,

i would like to read a temperature sensor on pin2 , how can i get this value ?

Thank you

Erel · Sep 2, 2014

I don't think that it is possible as the pin state is either high or low.

StarinschiAndrei · Sep 2, 2014

Erel said:
I don't think that it is possible as the pin state is either high or low.

This is not good news for me , do you think that will be possible in near future to read values from GPIO pins ?

Erel · Sep 3, 2014

I've uploaded a new beta version that allows you to provision an analog input pin. I haven't tested this functionality.

Initialize a GpioPinAnalogInput object and then read the value with pin.Value. You should use a timer to periodically read the value.

StarinschiAndrei · Sep 12, 2014

Than

Erel said:
I've uploaded a new beta version that allows you to provision an analog input pin. I haven't tested this functionality.

Initialize a GpioPinAnalogInput object and then read the value with pin.Value. You should use a timer to periodically read the value.

Thank you,

StarinschiAndrei · Sep 12, 2014

StarinschiAndrei said:
Than

Thank you,

Hi Erel,
I try the new version with different pins (1,4 and the last was 16) below the code and the error message

B4X:

Sub Process_Globals
Private controller As GpioController
  Private pin16 As GpioPinAnalogInput

  'Private pin1 As GpioPinDigitalOutput
Private timer1 As Timer
End Sub

Sub AppStart (Args() As String)
    controller.Initialize
pin16.Initialize(16)
  Log("Monitoring Pin2 state")
    timer1.Initialize("Timer1", 1000)
      timer1.Enabled = True
  StartMessageLoop
End Sub
Sub timer1_tick
    Log(pin16.Value)
End Sub

woniol · Sep 12, 2014

I haven't tried this yet, but the RPi pins are all digital. To use analog input you will probably need another circuit with an interface to the Pi.

StarinschiAndrei · Sep 12, 2014

woniol said:
I haven't tried this yet, but the RPi pins are all digital. To use analog input you will probably need another circuit with an interface to the Pi.

Yes i know. i use an LM35 temperature sensor it is similar with is on the following example http://www.cl.cam.ac.uk/projects/raspberrypi/tutorials/temperature/ and also i saw many example with this circuit but with python.

woniol · Sep 12, 2014

LM35 is not similar to DS18b20.
LM35 is analog temperature sensor - it gives analog output
DS18b20 is digital temperature sensor - is uses 1wire bus for data output.

1wire is not yet supported by pi4j

Plese have a look at DS1621 - it uses i2c bus supported by pi4j.

StarinschiAndrei · Sep 12, 2014

woniol said:
LM35 is not similar to DS18b20.
LM35 is analog temperature sensor - it gives analog output
DS18b20 is digital temperature sensor - is uses 1wire bus for data output.

1wire is not yet supported by pi4j

Plese have a look at DS1621 - it uses i2c bus supported by pi4j.

Yes , you are right. I found this how to read analog sensor, i didn't tested but sounds good.
https://learn.adafruit.com/basic-resistor-sensor-reading-on-raspberry-pi/overview
probably i will buy MCP3008 chip this is the easiest solution

woniol · Sep 12, 2014

I will try to find some time this weekend and write a class for DS1621 with pi4j.

Michael1968 · Sep 12, 2014

woniol said:
LM35 is not similar to DS18b20.
LM35 is analog temperature sensor - it gives analog output
DS18b20 is digital temperature sensor - is uses 1wire bus for data output.

1wire is not yet supported by pi4j

Plese have a look at DS1621 - it uses i2c bus supported by pi4j.

Hi Woniol
to use DS18b20 it's very easy

Load the Kernel Modul:
$sudo modprobe w1-gpio
$sudo modprobe w1-therm

this creates a folder:
/sys/bus/w1/devices/10-00080293bd31
10-00080293bd31 is the rom-ID of the DS18b20

in this folder there is a file named w1_slave with the temperature

I read the file with textreader line by line to get the temperature
it works perfect for me

Best regards
Michael

YIM bunchhat · Sep 26, 2014

Hi Erel,

I try to test your code but I got an error don't know why?

B4J Library [IoT] jPi4J - Raspberry Pi GPIO controller

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