RASPBERRY PI WITH JAVA 8 + Pi4J (Devoxx 2014)

Raspberry Pi with Java 8 + Pi4J
Robert Savage
Software Architect, MTS
Harman International
#DV14 #pi4j @savageautomate

What is Pi4J?
Pi4J is an open-source project providing a library for Java
programmers to interact with the low-level I/O capabilities
on the Raspberry Pi platform.
www.pi4j.com
• Open Source Project
• Low Level I/O Library
• Object-Oriented API
• Event Based
• Java & C (JNI + Native)

Pi4J Supported I/O
Digital Interfaces
• GPIO
(General Purpose Input/Output)
Data Interfaces
• UART, SERIAL
(Universal Asynchronous Receiver/Transmitter)
• SPI
(Serial Peripheral Interface)
• I2C
(Inter-Integrated Circuit)
Analog Interfaces*

GPIO
• Input or Output
• Digital States
• HIGH = +3.3 VDC
• LOW = 0 VDC
• RPi Models
• A B = ~21 GPIO
• B+ = 28 GPIO
• Compute Module = 46 GPIO

Pi4J GPIO Pin Addressing
Visit pi4.com for a detailed pin addressing diagram!

GPIO Outputs
• Control Things
(ON OFF)

GPIO Output Circuit

GPIO Output Example
//
create
GPIO
controller
final
GpioController
gpio
=
GpioFactory.getInstance();
//
create
GPIO
output
pin
final
GpioPinDigitalOutput
output
=
gpio.provisionDigitalOutputPin(
RaspiPin.GPIO_12,
PinState.LOW);
//
control
GPIO
output
pin
output.high();
output.low();
output.toggle();
//
invert
current
state
output.pulse(1000);
//
set
state
for
a
limited
duration

GPIO Output Circuit
Active-High Relay Board
12 VDC
Strobe
Light
12 VDC
Illuminated
Switch
12 VDC
Power Source

GPIO Output Demo
• Sample Code
• Live Demo

GPIO Inputs
• Monitor Things
• ON OFF
• Open Close

GPIO Input Circuit

GPIO Input Reference
• GPIO inputs require a “reference” voltage.
• Without a reference, a GPIO pin can “float”
• The Raspberry Pi includes internal PULL-UP and
PULL-DOWN resistor settings that can be configured
via Pi4J.

• PULL-DOWN
Resistance provides a reference (bias) to
GROUND (0 VDC). If your circuit expects to
provide +3.3VDC to signal the GPIO pin HIGH,
then you need a PULL-DOWN reference.
• PULL-UP
Resistance provides a reference (bias) to
+3.3 VDC. If your circuit expects to provide
GROUND to signal the GPIO pin LOW, then
you need a PULL-UP reference.

Alternatively, you can build the PULL-UP or PULL-DOWN
reference in the hardware circuit. The circuit below
demonstrates a PULL-UP resistor at R1.
This circuit signals the GPIO
input pin to LOW when the
switch closes the circuit and a
path to GROUND is complete.
PULL-UP
RESISTOR

GPIO Input Example
//
create
GPIO
controller
final
GpioController
gpio
=
GpioFactory.getInstance();
//
create
a
GPIO
input
pin
final
GpioPinDigitalInput
input
=
gpio.provisionDigitalInputPin(
RaspiPin.GPIO_02,
PinPullResistance.PULL_DOWN);

GPIO Input Listener Example
//
create
event
listener
for
GPIO
input
pin
input.addListener((GpioPinListenerDigital)
Java 8
Lambda
(GpioPinDigitalStateChangeEvent
event)
-‐
{
//
set
output
state
to
match
the
input
state
output.setState(event.getState());
});

GPIO Input Demo
• Sample Code
• Live Demo

Pi4J Component API
• The component APIs provides an abstraction layer from the
hardware I/O layer.
• This allows hardware design/circuitry to change with *less* impact
to your implementation code.
• For example, a RELAY could be controlled from GPIO, RS232, SPI, or
I2C. You program defines the RELAY impl up front based on the
hardware interface, but the rest of your program logic works against the
RELAY component interface and not the direct hardware /communication
IO interfaces.

Component Interfaces
• Keypad
• Light / LED
• Dimmable Light
• LCD
• Power Controller
• Relay
• Momentary Switch
• Toggle Switch
• Analog Sensor
• Distance Sensor
• Motion Sensor
• Temperature Sensor

GPIO Components Example
//
create
LED
component
final
Light
light
=
new
GpioLightComponment(output);
//
usage
example
light.on();
(or)
light.off();
//
create
momentary
switch
component
final
MomentarySwitch
ms
=
new
GpioMomentarySwitchComponment(
input,
PinState.LOW,
//
“OFF”
pin
state
PinState.HIGH);
//
“ON”
pin
state

Component Demo
• Sample Code
• Live Demo

UART / Serial / RS-232
• The Raspberry Pi supports on on-board UART for
serial communication.
• Pi4J supports basic serial communication.
• To use RS232 serial communication a level-shifter is
required to convert between the TTL voltage levels
(+3.3 VDC) and those required for RS232
communication.

RS-232 Level Shifter

USB to RS-232 Adapter
In addition to the on-board UART, you can also use a USB to
RS232 adapter connected to the Raspberry Pi to provide
RS232 serial communication.

UART / RS-232 Example
//
create
an
instance
of
the
serial
communications
class
final
Serial
serial
=
SerialFactory.createInstance();
//
open
the
default
serial
port
provided
on
the
P1
header
//
(this
is
where
our
LED
reader
is
connected)
serial.open(Serial.DEFAULT_COM_PORT,
2400);
//
send
Hello
World
message
to
sign
serial.writeln(ID01PACLHello
World!
-‐-‐
);
serial.writeln(ID01RPA);

UART / RS-232 Listener Example
//
create
and
register
the
serial
data
listener
serial.addListener((SerialDataListener)
Java 8
Lambda
(SerialDataEvent
event)
-‐
{
//
print
out
the
data
received
to
the
console
System.out.println(event.getData());
});

UART / RS-232 Demo
• Sample Code
• Live Demo

Putting It All Together
Lets create a real-world demo using a Raspberry
Pi, Java, Pi4J, GPIO Inputs Outputs, and RS232
(Serial) devices to do something useful.

Demo Project Goal
• Create a sophisticated model rocket launching
platform.

Demo Project Requirements
• Implement a safety key
switch to arm the rocket
and protect from
accidental launch ignition.
• Implement a launch
activation button to
initiate a launch sequence.

• Implement an audible safety
alarm to alert spectators of
launch ready conditions.
• Implement a visible alert
device to notify spectators
of launch ready conditions.

• Implement an abort button
to abort the launch sequence.
• Implement a safety IR beam
detector to abort launch if a
person approaches the launch
pad.

• Implement an LED message board to show
spectators the countdown and phases of the
launch.
• Implement a countdown timer for the launch
sequence.

• Implement an on-screen console/dashboard

Demo Project
• Sample Code
• Live Demo

Sides source code available now at http://www.savagehomeautomation.com/devoxx

RASPBERRY PI WITH JAVA 8 + Pi4J (Devoxx 2014)

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