Java Webinar #9: “Raspberry Pi Platform for Java Programmers”
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Pi4J is an open source Java library that provides an abstraction layer for interacting with Raspberry Pi's GPIO pins and other hardware interfaces like I2C and SPI. It aims to simplify GPIO programming for Java developers by presenting an object-oriented API. Pi4J has evolved over several major versions, with version 2.0 introducing a plugin architecture and migrating to a more standard Broadcom pin numbering scheme. The library provides classes for configuring pins as inputs or outputs, reading from and writing to pins, attaching listeners to respond to pin state changes, and interacting with common hardware components.
Java Webinar #9: “Raspberry Pi Platform for Java Programmers”
- 2. 2 Confidential Raspberry Pi Platform for Java Programmers Dmytro Ihnatiev Raspberry Pi Platform for Java Programmers 29.04.2021
- 3. 3 3 Confidential Raspberry Pi general overview
- 4. 4 Confidential What is Raspberry Pi • Single Board Computer • Linux Operating system - Raspbian • ARM Architecture • Low Cost • Low Power • Has the ability to interact with the outside world GPIO (used in a wide array of digital maker projects, from music machines and parent detectors to weather stations and tweeting birdhouses with infra-red cameras, etc.)
- 5. 5 Confidential Raspberry Pi other models Raspberry Pi Pico Raspberry Pi 400 unit
- 6. 6 Confidential 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
- 7. 7 Confidential Ground Pin, Power Pin, GPIO what is it? The Raspberry Pi 4 board has a GPIO header with 40 pins (amount could be different from model to model). Ground Pins The ground is very useful for making a common reference between all components in your circuit. Always remember to connect all components to the ground. Power Pins Those pins can be used to power components such as sensors or small actuators. GPIO GPIO means General Purpose Input/Output. Basically that’s one pin you can use to write data to external components (output), or read data from external components (input).
- 8. 8 Confidential Pin numbering example (Pinout)
- 9. 9 9 Confidential Java (Pi4J) for Raspberry Pi
- 10. 10 Confidential What is Pi4J? • Open Source Project • Raspberry Pi Platform (Linux/ARM) • Abstraction over Low Level I/O • Supports I/O Programming • Object-oriented API • Event Based • Java / C (JNI + Native) • Provides Listeners , Triggers & Component API • Provides Java Classes supporting I/O Operations
- 11. 11 Confidential Brief history of Pi4J The Pi4J Project was started in 2012, the same year the Raspberry Pi was introduced as a tool to provide Java developers a simple and familiar object-oriented interface library to access the low-level I/O capabilities of the Raspberry Pi including GPIO, I2C, SPI, PWM and Serial communications.
- 12. 12 Confidential Version 1.4 of Pi4J The original library which started in 2012 and got a last release in 2021. Up till version 1.3 the library targets Java 8, while version 1.4 relies on Java 11. Main features: • Export & unexport GPIO pins • Configure GPIO pin direction • Configure GPIO pin edge detection • Control/write GPIO pin states • Pulse GPIO pin state • 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
- 13. 13 Confidential Version 2 of Pi4J As of Version 2.0, Pi4J will no longer include support for peripheral devices and add-on chipsets/boards as part of the core project. A new plugin model has been introduced in version 2.0 that should help enable third-party development and support third-party add-ons which may be developed and maintained independently of the core Pi4J project. Main features: • Fluent APIs/Interfaces • Immutable Runtime Context • Extensible Provider/Platform/Plug-in Architecture • Builder-patterns for creating new I/O instances • Dependency Injection via Pi4J Annotations • Well-documented source code • Hardware PWM Support • Remote I/O Support (via TCP/IP) • Java 11 • In addition to the features listed above, Pi4J version 2.0 also abandons the old WiringPi pin numbering scheme in favor of the more traditional and commonly used Broadcom pin numbering scheme.
- 14. 14 Confidential Version 2 of Pi4J As of Version 2.0, Pi4J will no longer include support for peripheral devices and add-on chipsets/boards as part of the core project. A new plugin model has been introduced in version 2.0 that should help enable third-party development and support third-party add-ons which may be developed and maintained independently of the core Pi4J project. Main features: • Fluent APIs/Interfaces • Immutable Runtime Context • Extensible Provider/Platform/Plug-in Architecture • Builder-patterns for creating new I/O instances • Dependency Injection via Pi4J Annotations • Well-documented source code • Hardware PWM Support • Remote I/O Support (via TCP/IP) • Java 11 • In addition to the features listed above, Pi4J version 2.0 also abandons the old WiringPi pin numbering scheme in favor of the more traditional and commonly used Broadcom pin numbering scheme.
- 15. 15 Confidential 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 • 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
- 16. 16 Confidential Main design classes (Pi4J 1.4) • Listeners. Provides the ability to react on events from triggers • Triggers. Create an event on state change • Components (Deprecated in Pi4J 2.0) Other Components • Pull up and Pull down Resistors • Toggle output and handy methods to access pins and change their states
- 17. 17 Confidential Pull up and Pull Down resistors The pull-down resistor pulls the voltage down to zero. If the pull-up switch is pressed, it pulls the voltage up to whatever the + supply is. The pull-up resistor pulls the voltage up to whatever the + supply is. If the pull-down switch is pressed, it pulls the voltage down to zero.
- 18. 18 Confidential GPIO Output Circuit Example 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
- 19. 19 Confidential GPIO Input Circuit Example GpioController gpio = GpioFactory.getInstance(); GpioPinDigitalInput input = gpio.provisionDigitalInputPin(RaspiPin.GPIO_02, PinPullResistance.PULL_DOWN); input.addListener((GpioPinListenerDigital) (GpioPinDigitalStateChangeEvent event) -> { System.out.println( "State = " + event.getState() + ", Edge = " + event.getEdge() + ", Pin = " + event.getPin() + ", Pressed = " + input.isHigh() ); } );
- 20. 20 Confidential Resources • Pi4J - https://pi4j.com/1.2/index.html • GitHub Pi4J - https://github.com/Pi4J/pi4j • Pi4J 2.0 - https://pi4j.com/ • GPIO - https://www.raspberrypi.org/documentation/usage/gpio/README.md • WiringPi - http://wiringpi.com/ • Extensive support for many devices for many languages - https://github.com/ControlEverythingCom • 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 (CanaKit, Adeept, etc.)
- 21. 21 Confidential