Published October 29, 2017 © Apache-2.0

Decibels Indicator

A way to visualize how noisy is our open space office.

BeginnerFull instructions provided2 hours1,599

Things used in this project

Hardware components

Raspberry Pi 3 Model B

Or any Android Things compatible board

Adafruit Mini USB Microphone

APA102 RGB LED Strip (60 LEDs/m)

You can use any APA102 LED strip

SparkFun Breadboard Power Supply 5V/3.3V

Breadboard (generic)

Software apps and online services

Google Android Things

Story

Do you like noisy open plan offices? Neither do we! This project helps visualizing the amount of decibels in real time, to encourage employees to work more calmly.

Creating the device

The device is really easy to build. We only need an Android Things board (e.g. a Raspberry Pi 3), an USB microphone and an APA102 LED strip. See the schematics below for additional information.

Getting the decibel value

The USB microphone will record audio using the MediaRecorder from the Android SDK. Since we do not want to keep the audio file, both for security and privacy reasons, but also because the device internal space is limited, we will record to /dev/null. Then, we can call the mediaRecorder.maxAmplitude method every 250ms to get the sound pressure value and convert it to decibels using the following formula:

val decibels = 20 * Math.log10(volume.toDouble()).toFloat()

Once we have the decibels value, we can forward this data to the LED strip.

Displaying the decibel value with the LED strip

We are going to use the driver-apa102 from the official contrib-drivers github repository. First, we need to initialize the LED strip:

@OnLifecycleEvent(Lifecycle.Event.ON_START)
fun start() {
 ledStrip = Apa102(SPI_NAME, LED_MODE).apply {
   brightness = LED_BRIGHTNESS
   write(IntArray(NUM_LEDS))
 }
}

Then, we need to show the decibels. Our LED strip has 60 LEDS. It should start from Green to Red, which means in HSB from 90° to 0°.

val colors = IntArray(NUM_LEDS)
 
for (i in 0 until NUM_LEDS) {
    colors[i] = Color.HSVToColor(255, floatArrayOf((HSV_GREEN - (i.toFloat() * (HSV_GREEN - HSV_RED) / (NUM_LEDS - 1)) + 360) % 360, 1.0f, 1.0f))
}
ledStrip!!.write(colors)

The LED strip will look like that:

Our LED strip

To show a progress bar, we will turn off LEDs above the current amount of decibels setting the color to 0:

var decibelLevel: Float
for (i in 0 until NUM_LEDS) {
    decibelLevel = i.toFloat() * (MAX_DECIBELS - MIN_DECIBELS) / (NUM_LEDS - 1) + MIN_DECIBELS
    colors[i] = if (decibels > decibelLevel) getColor(i) } else 0
}
ledStrip!!.write(colors)

And we have our decibel indicator working!

Going further?

This would be a good idea to periodically send those data into Google Cloud IoT Core, so that we could inspect those data over the time, and potentially add some machine learning to detect abnormal noisy behaviors and warn people when they are making too much noise.

Code

// Every 250ms, we will get the decibel value
class DecibelsLiveData(private val frequencyMs: Long = 250) : LiveData<Float>() {

    companion object {
        private const val HANDLER_MSG_GET_DECIBELS = 1
    }

    private val mediaRecorder = MediaRecorder()
    private var handler: Handler? = null
    private var handlerThread: HandlerThread? = null

    private val handlerCallback = { msg: Message ->
        if (msg.what == HANDLER_MSG_GET_DECIBELS) {
            // Get the sound pressure value
            val volume = mediaRecorder.maxAmplitude
            if (volume != 0) {
                // Change the sound pressure value to the decibel value and post it
                val decibels = 20 * Math.log10(volume.toDouble()).toFloat()
                postValue(decibels)
            }

            handler?.sendEmptyMessageDelayed(HANDLER_MSG_GET_DECIBELS, frequencyMs)
        }
        true
    }

    override fun onActive() {
        startRecording()
    }

    override fun onInactive() {
        stopRecording()
    }

    // Records to /dev/null (we don't need to keep the recording, we only need to get the sound pressure value)
    fun startRecording() {
        with(mediaRecorder) {
            try {
                reset()
                setAudioSource(MediaRecorder.AudioSource.MIC)
                setOutputFormat(MediaRecorder.OutputFormat.THREE_GPP)
                setAudioEncoder(MediaRecorder.AudioEncoder.AMR_NB)
                setOutputFile("/dev/null")

                prepare()
                start()

                // Start handler thread
                handlerThread = HandlerThread(TAG).also { handlerThread ->
                    handlerThread.start()
                    handler = Handler(handlerThread.looper, handlerCallback).also { handler ->
                        handler.sendEmptyMessage(HANDLER_MSG_GET_DECIBELS)
                    }
                }
            } catch (e: Exception) {
                Log.e("TAG", "Error initializing mediaRecorder", e)
            }
        }
    }

    fun stopRecording() {
        handler?.removeMessages(HANDLER_MSG_GET_DECIBELS).also { handler = null }
        handlerThread?.quitSafely().also { handlerThread = null }

        try {
            mediaRecorder.stop()
            mediaRecorder.release()
        } catch (e: IllegalStateException) {
            Log.e("TAG", "Error stopping mediaRecorder")
        }
    }
}

class LedStrip : LifecycleObserver {

    companion object {
        private const val SPI_NAME = "SPI0.0"
        private const val NUM_LEDS = 60
        private const val LED_BRIGHTNESS = 6 // 0 ... 31

        private const val HSV_GREEN = 90
        private const val HSV_RED = 0

        private const val MIN_DECIBELS = 30
        private const val MAX_DECIBELS = 90

        private val LED_MODE = Apa102.Mode.BGR
    }

    private var ledStrip: Apa102? = null
    private val colors = IntArray(NUM_LEDS)

    // Initialize the Apa102 LED strip
    @OnLifecycleEvent(Lifecycle.Event.ON_START)
    fun start() {
        ledStrip = Apa102(SPI_NAME, LED_MODE).apply {
            brightness = LED_BRIGHTNESS
            write(IntArray(NUM_LEDS))
        }
    }

    // Close the LED strip
    @OnLifecycleEvent(Lifecycle.Event.ON_STOP)
    fun stop() {
        ledStrip?.close().also { ledStrip = null }
    }

    // Show the decibels "progress bar"
    fun showDecibels(decibels: Float) {
        var decibelLevel: Float

        for (i in 0 until NUM_LEDS) {
            decibelLevel = i.toFloat() * (MAX_DECIBELS - MIN_DECIBELS) / (NUM_LEDS - 1) + MIN_DECIBELS

            colors[i] = if (decibels > decibelLevel) {
                Color.HSVToColor(255, floatArrayOf((HSV_GREEN - (i.toFloat() * (HSV_GREEN - HSV_RED) / (NUM_LEDS - 1)) + 360) % 360, 1.0f, 1.0f))
            } else {
                0
            }
        }
        ledStrip!!.write(colors)
    }
}