JUno

Arduino UNO R4 WiFi

The UNO R4 WiFi keeps the classic UNO form factor and 5 V GPIO while replacing the UNO R3's 8-bit AVR with a 32-bit Renesas RA4M1, and adds an ESP32-S3 module for Wi-Fi and Bluetooth, a 12 × 8 LED matrix and a Qwiic connector. Juno compiles for the RA4M1 with its Thumb-2 backend; the ArduinoUno device facade is the entry point for the board's peripherals. The UNO R4 Minima is not a Juno target.

Arduino UNO R4 WiFi

Core specification

Characteristic UNO R4 WiFi
Main microcontroller Renesas R7FA4M1AB3CFM (RA4M1)
CPU architecture 32-bit Arm Cortex-M4 with floating-point unit
CPU clock 48 MHz
Program flash 256 kB
SRAM 32 kB
Logic and operating voltage 5 V
Digital I/O 14 pins, D0-D13 (6 with PWM)
Analog inputs 6 pins, A0-A5, up to 14-bit resolution
USB connector USB-C (native USB)
Built-in LED D13
Wireless coprocessor ESP32-S3-MINI-1-N8 (Wi-Fi and Bluetooth)
Onboard LED matrix 12 columns by 8 rows
Qwiic connector Yes, 3.3 V I2C
Arduino CLI FQBN arduino:renesas_uno:unor4wifi
Juno board id arduino-uno-r4-wifi

What Juno supports

Feature Status Notes Example
Gpio, DigitalOutput, analogRead, analogWrite ✓ Standard Arduino GPIO calls. Blink
Delay, Clock, Serial ✓ Serial over the native USB port.
Double-precision java.lang.Math ✓ MathFunctionsDoublePrecision
Threads, synchronized, locks, StructuredTaskScope, ScopedValue ✓ VirtualThreads, StructuredConcurrency
BigInteger, BigDecimal, MathContext ✓
UUID.randomUUID() ✓ The RA4M1's Secure Crypto Engine true-random-number generator.
@Watchdog ✓ The RA4M1 hardware watchdog.
Onboard LED matrix ✓ 12 × 8 through LedMatrix and LedCanvas. LedMatrixScrollingText
USB HID mouse ✓ ArduinoUno.getMouse() through the Arduino Mouse library. RatonLoco
Servo ✓ Through the Arduino Servo library. ServoSweep
Wi-Fi station and access point ✓ Through the ESP32-S3 and WiFiS3.
HttpClient (HTTP and HTTPS) ✓ SingleHttpsGet
HttpServer ✓ HttpServerBacklight
Smtp, Pop3Client ✓ Implicit TLS and STARTTLS (STARTTLS needs the ESP_SSLClient library). EmailClient
Bluetooth LE (LEGO Powered Up) ✓ Through ArduinoBLE; see LEGO.
SdCard ✓ On a shield's microSD slot; see Shields. SdFileOperations

Features

These need only the UNO R4 WiFi and its USB-C cable.

DigitalOutput led = DigitalOutput.of(ArduinoUno.getGpio().getBuiltinLed());

while (true) {
    led.high();
    Delay.millis(500);
    led.low();
    Delay.millis(500);
}

Blink is the complete program; it builds for any board, so pass -Djuno.board=arduino-uno-r4-wifi.

Scroll text on the LED matrix

The matrix is 12 columns by 8 rows. LedCanvas draws into a frame and show sends it to the matrix:

LedMatrix matrix = ArduinoUno.getLedMatrix();
matrix.begin();
boolean[][] frame = new boolean[LedCanvas.HEIGHT][LedCanvas.MAX_WIDTH];

for (int offset = 12; offset >= -60; offset--) {
    LedCanvas.clear(frame);
    LedCanvas.drawText(frame, "Hello, Juno", offset, 0);
    LedCanvas.show(frame);
    Delay.millis(80);
}

drawText takes a compile-time string literal. LedMatrixScrollingText scrolls a longer message forever.

USB HID mouse

ArduinoUno.getMouse() makes the board a USB mouse for the computer it is plugged into. Call begin() once, then move(x, y) moves the pointer by that many pixels:

Mouse mouse = ArduinoUno.getMouse();
mouse.begin();

while (true) {
    mouse.move(50, 0);   // right
    Delay.millis(1000);
    mouse.move(0, 50);   // down
    Delay.millis(1000);
    mouse.move(-50, 0);  // left
    Delay.millis(1000);
    mouse.move(0, -50);  // up
    Delay.millis(1000);
}

Once uploaded, the program keeps moving the pointer; disconnect the board or upload another program to stop it. RatonLoco is the complete program.

Shields

Seat each shield directly on the UNO R4 WiFi. Check which pins a shield uses before stacking two: the LCD Keypad Shield's backlight and the Data Logger Shield's SD chip select are both D10.

TFT Touch Shield

ELEGOO 2.8-inch TFT Touch Shield

The ELEGOO 2.8" TFT touch shield is a 240 × 320 ILI9341 color display on an 8-bit parallel bus, with a resistive touch panel and a microSD socket; it needs no extra Arduino library. TftTouchShield draws through ParallelBus, a compiler intrinsic that writes a whole GPIO port per store through the RA4M1's port set/reset registers. The TFT Touch Shield API, wiring and touch calibration are on the Arduino Shields page.

TftTouchShield tft = new TftTouchShield();
tft.begin();
tft.setRotation(TftTouchShield.LANDSCAPE);
tft.fillScreen(TftTouchShield.BLACK);
tft.setCursor(10, 10);
tft.setTextSize(2);
tft.setTextColor(TftTouchShield.YELLOW, TftTouchShield.BLACK);
tft.print("Hello, Juno");

while (true) {
    if (tft.readTouch()) {
        tft.fillCircle(tft.touchX(), tft.touchY(), 3, TftTouchShield.WHITE);
    }
}

TouchPaintTFT is a finger-paint program, and WeatherTFT a desk weather station that reads its Wi-Fi credentials from the shield's microSD card (TftTouchShield.getSdCard() on the shield instance, chip select D10).

Grove Base Shield

Grove Base Shield

The Grove Base Shield is passive: every socket is an ordinary UNO pin, and GroveBaseShield names them so programs don't hard-code numbers. Plug a Grove module in and pass the socket's getter to its driver; the socket supplies the module's GND and VCC. A Grove DHT22 temperature and humidity sensor in the D4 socket:

GroveBaseShield shield = new GroveBaseShield();
GroveDht22 dht = new GroveDht22();
int[] reading = new int[GroveDht22.READING_LENGTH];
int[] frame = new int[GroveDht22.FRAME_LENGTH];

if (dht.read(shield.getD4(), reading, reading.length, frame, frame.length)) {
    Serial.print(reading[GroveDht22.TEMPERATURE_TENTHS_CELSIUS]);
    Serial.println(" tenths of a degree");
}

SupabaseGroveTemperatures reads three Grove temperature sensors on this shield once a minute and publishes them to Supabase. See Grove for the sensor drivers.

Arduino 9 Axis Motion Shield

Arduino 9 Axis Motion Shield

The shield's Bosch BNO055 fuses its accelerometer and gyroscope itself and reports the heading in degrees. NineAxisMotionShield reads it over I2C as plain Java, with no Arduino library. The heading is relative to the direction the sensor pointed at begin(), which suits measuring how far a vehicle has turned. begin() drives D7, the sensor's reset line, so don't use D7 for anything else:

NineAxisMotionShield imu = new NineAxisMotionShield();
if (imu.begin()) {
    int start = imu.headingDegrees();
    while (true) {
        Serial.println(imu.turnedSince(start));   // degrees turned, clockwise positive
        Delay.millis(200);
    }
}

NineAxisMotionShieldSerial prints heading, pitch, gyro and calibration readings.

LCD Keypad Shield

LCD Keypad Shield

A 16 × 2 character LCD with five buttons read through one analog pin (A0). LcdKeypadShield needs no extra library: the LCD uses D4-D9 and its backlight D10.

LcdKeypadShield lcd = new LcdKeypadShield();
lcd.begin();
lcd.print("Hello, Juno");

while (true) {
    if (lcd.readButton() == LcdKeypadShield.SELECT) {
        lcd.setCursor(0, 1);
        lcd.print("SELECT pressed");
    }
    Delay.millis(100);
}

LcdKeypadDemo shows each button press, and Pomodoro is a Pomodoro timer.

AZDelivery Data Logger Shield

AZDelivery Data Logger Shield

A microSD socket on the UNO's SPI pins (chip select D10, MOSI D11, MISO D12, SCK D13), plus a DS1307 real-time clock that Juno does not drive. Format the card as FAT16 or FAT32. Keep the network's credentials on the card rather than in the source: put wifi.ssid and wifi.password in application.properties at the card's root, then:

SdCard sd = new DataLoggerShield().getSdCard();
Wifi wifi = ArduinoUno.getWifi();

if (sd.begin()) {
    try (InputStream file = sd.open("application.properties")) {
        if (file != null) {
            Properties properties = new Properties();
            properties.load(file);
            wifi.begin(properties.getProperty("wifi.ssid"), properties.getProperty("wifi.password"));
        }
    }
}

WifiStatusSD joins the network this way and prints its status; SdFileOperations exercises every SdCard file operation.

Build and run

Run juno:install-deps once to install the Renesas UNO core and the optional libraries the examples need (Mouse, ArduinoBLE, ESP_SSLClient, Servo, SdFat). Then compile and upload an example, for instance the virtual-threads demo:

./mvnw -f juno-examples/pom.xml juno:install-deps
./mvnw -f juno-examples/pom.xml compile juno:upload \
  -Djuno.main=io.github.jabrena.juno.language.VirtualThreads \
  -Djuno.board=arduino-uno-r4-wifi

Open the serial monitor in another terminal:

./mvnw -f juno-examples/pom.xml juno:monitor \
  -Djuno.board=arduino-uno-r4-wifi

The monitor uses 115200 baud by default, matching Serial.begin(BaudRate.BAUD_115200).