Raspberry Pi 3 running Android Things driving an Arduino Uno to control an RGB LED

README.md

Demo video: https://goo.gl/photos/a4Ge3j8a32Sy2KoS6

To control an RGB LED, we need 3 PWM pins. The Raspberry Pi 3 only has one. Sad.

But the Arudino Uno I had sitting behind me that I've literally never opened has 6 PWM pins...more than enough!

So now...

• The Raspberri Pi is running my Android Things app
• That app sends messages over a serial conncetion to the Arduino
• The Arudino controls the LED.

Circuit diagram for the LED is here: https://www.sunfounder.com/learn/Super_Kit_V2_for_RaspberryPi/lesson-5-rgb-led-super-kit-for-raspberrypi.html

Raspberry Pi GPIO to Arduino GPIO Pins are as follows:

• Raspberry Pi 3 Ground -> Arduino Uno Ground
• Raspberry Pi 3 Pi GPIO14 -> Arduino Uno GPIO 0/RX
• Raspberry Pi 3 Pi GPIO15 -> Arduino Uno GPIO 1/TX

We need to add in the extra pins because USB devices are not support with Android Things Preview 1 (see: https://plus.google.com/112090467711235891544/posts/78pNQa52Li2). The USB connection from the Arudino in the video above is just for power.

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
              android:layout_width="match_parent"
              android:layout_height="match_parent"
              android:orientation="vertical"
              android:padding="24dp">

    <TextView
        android:id="@+id/red_label"
        style="?android:textAppearanceLarge"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"/>

    <SeekBar
        android:id="@+id/red"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginBottom="24dp"/>

    <TextView
        android:id="@+id/green_label"
        style="?android:textAppearanceLarge"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"/>

    <SeekBar
        android:id="@+id/green"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginBottom="24dp"/>

    <TextView
        android:id="@+id/blue_label"
        style="?android:textAppearanceLarge"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"/>

    <SeekBar
        android:id="@+id/blue"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"/>

</LinearLayout>

arduino.ino

int redPin = 9;
int greenPin = 10;
int bluePin = 11;

void setup() {
  // initialize serial:
  Serial.begin(9600);
  
  // make the pins outputs:
  pinMode(redPin, OUTPUT);
  pinMode(greenPin, OUTPUT);
  pinMode(bluePin, OUTPUT);
}

void loop() {
  while (Serial.available() > 0) {
    int red = Serial.parseInt();
    int green = Serial.parseInt();
    int blue = Serial.parseInt();

    if (Serial.read() == '\n') {
      analogWrite(redPin, red);
      analogWrite(greenPin, green);
      analogWrite(bluePin, blue);
    }
  }
}

MainActivity.kt

package com.madebyatomicrobot.things

import android.app.Activity
import android.os.Bundle
import android.util.Log
import android.widget.SeekBar
import android.widget.SeekBar.OnSeekBarChangeListener
import android.widget.TextView
import com.google.android.things.pio.PeripheralManagerService
import com.google.android.things.pio.UartDevice
import java.io.IOException
import java.nio.charset.Charset

class MainActivity : Activity(), OnSeekBarChangeListener  {
    companion object {
        private val TAG = MainActivity::class.java.simpleName
    }

    lateinit var redLabelView : TextView
    lateinit var greenLabelView : TextView
    lateinit var blueLabelView : TextView

    lateinit var redBarView : SeekBar
    lateinit var greenBarView : SeekBar
    lateinit var blueBarView : SeekBar

    lateinit var device : UartDevice

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        redLabelView = findViewById(R.id.red_label) as TextView
        greenLabelView = findViewById(R.id.green_label) as TextView
        blueLabelView = findViewById(R.id.blue_label) as TextView

        redBarView = findViewById(R.id.red) as SeekBar
        greenBarView = findViewById(R.id.green) as SeekBar
        blueBarView = findViewById(R.id.blue) as SeekBar

        redBarView.max = 255
        greenBarView.max = 255
        blueBarView.max = 255

        redBarView.setOnSeekBarChangeListener(this)
        greenBarView.setOnSeekBarChangeListener(this)
        blueBarView.setOnSeekBarChangeListener(this)

        val manager = PeripheralManagerService()
        try {
            Log.i(TAG, "UART: " + manager.uartDeviceList)

            device = manager.openUartDevice("UART0")

            device.setBaudrate(9600)
            device.setDataSize(8)
            device.setParity(UartDevice.PARITY_NONE)
            device.setStopBits(1)

            showColor(0, 0, 0)
        } catch (ex: IOException) {
            Log.w(TAG, "Error in onCreate", ex)
        }
    }

    override fun onDestroy() {
        super.onDestroy()
        try {
            device.close()
        } catch (ex: IOException) {
            Log.w(TAG, "Error in onDestroy", ex)
        }
    }

    override fun onProgressChanged(seekBar: SeekBar?, progress: Int, fromUser: Boolean) {
        val red = redBarView.progress
        val green = greenBarView.progress
        val blue = blueBarView.progress

        showColor(red, green, blue)
    }

    override fun onStartTrackingTouch(seekBar: SeekBar?) {
        // Don't care
    }

    override fun onStopTrackingTouch(seekBar: SeekBar?) {
        // Don't care
    }

    fun showColor(red: Int, green: Int, blue: Int) {
        redLabelView.setText("Red ($red)")
        greenLabelView.setText("Green ($green)")
        blueLabelView.setText("Blue ($blue)")

        val serialMessage = "$red $green $blue\n"
        val bytes = serialMessage.toByteArray(Charset.forName("ASCII"))
        device.write(bytes, bytes.size)
    }
}

How is an app on a tablet connected serially to an embedded device? Is it an USB cable? And do these amateur boards have Bluetooth? Classic or Low Energy?