1. Java Programming on the Raspberry Pi with Pi4J
Rob Ratcliff

2. What is a Raspberry Pi? Single Board Computer – Pi 3 Model B+
Full-size HDMI
ARMv8 64-bit with 1.4 GHz
1 GB RAM
4 USB ports
40 I/O Pins for GPIO, UART, Serial and I2C
Ethernet, Wi-Fi and Bluetooth networking
CSI camera port for connecting a Raspberry Pi camera
Linux Operating System – Raspbian
ARM Hardware Architecture
Low Cost - $10 (Pi Zero) to $35 (Pi 3 Model B+) for Card
Low Power

3. Finding Compatible Hardware
Zillions of devices available
Search Amazon, Adafruit for Raspberry Pi devices
3.3V or 5V, I2C, GPIO, Serial
“Hats” can be used to expand capability by stacking boards

4. History of Pi4J
Open source library to interact with low-level I/O capabilities on the Raspberry Pi
First commit on github on 9/8/2012 by Robert Savage (Savage Home Automation)
82 outstanding issues, but stable
Runs on Java 8
Based on WiringPi C Library
and

5. Setup of the Raspberry Pi
SDCard Setup
Format Fat32 (exFat does not work)
Up to 64 GB supported, but has to be initially partitioned into 32 GB parts. Noobs will extend the 32 GB partition automatically. Raspbian can expand as well.
Noobs bootstrapper –
Unzip and copy contents to SD card’s root directory
Plug in monitor with HDMI cable and USB mouse and keyboard
Power on with microUSB cable and configure Raspbian
Reboot to Raspbian
Update OS – sudo apt-get update; sudo apt-get upgrade; sudo reboot
Add Hostname using sudo raspi-config
Install Bonjour/Zeroconf - Allows the PI to be accessed by hostname.local from your PC without DNS or knowing the DHCP IP address
sudo apt-get install libnss-mdns
On Windows, install Bonjour Print Service from Apple:
Setup account and SSH

6. Useful Tools socat – convert serial communications to Ethernet
i2c-tools - scan for and interact with I2C devices from the command line
Win32 Disk Imager – dump an image of your SD card to a file for backup or copying
tomcat8 – Java web server
VNC

7. IDE Setup
sudo update-alternatives –display java

8. NetBeans Automated Steps to Run Application on Pi
Compile code
Build a JAR file
SCP JAR file
Run application using SSH

9. Pi4J Capabilities Export & unexport GPIO pins
Configure GPIO pin direction
Configure GPIO pin edge detection – detect falling, rising edge for debounce
Control/write GPIO pin states
Pulse GPIO pin state - PWM
Read GPIO pin states
Listen for GPIO pin state changes (interrupt-based; not polling)
Automatically set GPIO states on program termination (GPIO shutdown)
Triggers for automation based on pin state changes
Send & receive data via RS232 serial communication
I²C Communication
SPI Communication
Extensible GPIO Provider interface to add GPIO capacity via expansion boards
Access system information and network information from the Raspberry Pi
Wrapper classes for direct access to WiringPi Library from Java

10. Protocols GPIO – General Purpose I/O
I²C – (I Squared C) – two wire communication using a signal and timer wire
Serial
USB
TCP/IP
UDP
Bluetooth

11. GPIO Input or Output Pins High (3.3 VDC) or Low (0 VDC) States
Outputs used to control things like relays, lights, motors, bells, etc.
Pullup and Pulldown resistors

12. GPIO Programming with Pi4J
Hardware Pins to Motorola Broadcom chipset numbering
Physical pin locations can change between board revisions
Pi4J can use Broadcom or WiringPi numbering schemes

13. Pi4J/WiringPi Board-Agnostic Numbering Scheme

14. GPIO Output Circuit GpioController gpio = GpioFactory.getInstance();
GpioPinDigitalOutput output =
gpio.provisionDigitalOutputPin(RaspiPin.GPIO_12, PinState.LOW);
output.high(); // set to high state
output.low(); // set to low state
output.toggle(); // switch to other state
output.pulse(1000); // set state for a duration
Credit: Robert Savage

15. GPIO Input Circuit GpioController gpio = GpioFactory.getInstance();
GpioPinDigitalInput input = gpio.provisionDigitalInputPin(RaspiPin.GPIO_02,
PinPullResistance.PULL_DOWN);
input.addListener(
new GpioPinListenerDigital() {
public void handleGpioPinDigitalStateChangeEvent(GpioPinDigitalStateChangeEvent event) {
System.out.println(
"State = " + event.getState() +
", Edge = " + event.getEdge() +
", Pin = " + event.getPin() +
", Pressed = " + input.isHigh() ); }
// Lambdas work as well
input.addListener((GpioPinListenerDigital) (GpioPinDigitalStateChangeEvent event) -> {System.out.println(event) } );

16. GPIO Input Reference
GPIO inputs require a reference voltage to prevent the pin from floating or picking up extraneous voltages
A “Pull Up” or “Pull Down” resistor setting can be specified on the Raspberry Pi using Pi4J

17. I²C Originally developed by Phillips in 1982
Multi-Master Multi-Slave Communication model
Two wires – clock driven by Master and Data from Slave or Master
Speeds: 100 kbs (standard), 400 kbs (full speed), 1 mbs (fast) and 3.2mbs
Device addressed by unique ID, 7 bit address

18. I²C Programming with Pi4J
I²C pins must be enabled using the raspi-config
Multiple I²C devices can be connected to the RaspberryPi
Use “sudo i2cdetect -y 1” to see registered I2C addresses for bus 1
Access data a byte at a time
Most significant byte (MSB) is first read
Vendor documentation can be confusing. Use open source code to gain clarification.

19. Angle Sensor Example ADC121C021
Potentiometer with SeedStudio Grove Socket

20. Remote Control of Devices
Any network protocol that Java 8 supports
MQTT – Message Queuing Telemetry Transport
Asynchronous messaging
Pub/Sub architecture
DIRMI – RMI replacement that supports bi-directional communication over a single socket and more QoS attributes in a Java-centric architecture – client/server model
Web sockets, REST, etc.
Can use socat to convert serial and other protocols to UDP or TCP/IP for easy access

21. Resources
Raspberry Pi with Programming the Internet of Things by Stephen Chin and James Weaver
- source code for pi4j
- source code for book
Extensive support for many devices for many languages
– C library that is the foundation of pi4j
A Few Hardware Vendors
SeeedStudio Grove
Adafruit – Provides Python code for most of their hardware
Texas Instruments (sold by Mouser, DigiKey, etc.)
Pi Starter and Learning Kit Vendors – Lots of others on Amazon
Adeept - Adeept New Ultimate Starter Learning Kit for Raspberry Pi 3 2 Model B/B+ Python ADXL345 GPIO Cable DC Motor
CanaKit - CanaKit Raspberry Pi 3 Complete Starter Kit - Includes 32 GB Samsung EVO+CanaKit Raspberry Pi 3 Complete Starter Kit - Includes 32 GB Samsung EVO+