Arduino-AudioKitOSX Demo Project

Overview

This project demonstrates how an OSX oscillator app created with AudioKit can be controlled by an Arduino via serial communication. A demo video shows the project in action.

Arduino Sketch

The schematic below shows the two potentiometers and SPDT (single pole - double throw) switch used to control the OSX app:

The assembled circuit:

The Arduino sketch is found in the SerialInputReading folder. The data from the potentiometers and the SPDT switch is read by the readAndSendPotentiometerDataIfChanged method. This method is called in the void loop(), so that the potentiometer values are checked exectued as long as the Arduino sketch is running.

First, a variable is created that reads the the input value for the analog pin that the potentiometer is connected to. The first potentiometer's data is read on Analog Input 0 (A0), and the second potentiometer's data is read on Analog Input 1 (A1).

///Potentiometer One
// Read the input on analog pin 0:
int potentiometerOneValue = analogRead(A0);

Then, the raw value from the potentiometer (the Arduino reads analog input as values to between 0 and 1023) to be a voltage value between 0 and 1:

int potOneVoltageValue = potentiometerOneValue * (1.0 / 1023.0);

Next, the value of the potentiometer is printed through the serial output. The format below is used so that the SerialCommunicator can correctly parse the values from the serial bus.

Serial.print("!pot1");
Serial.print(potOneVoltageValue);
Serial.print(";");

The readAndSendSwitchDataIfChanged method reads the state of the SPDT switch, which will be used to switch the instrument on and off, and is also called in the void loop().

The pin the switch is attached is digital pin 2: const int switchPin = 2;

The switch's state (whether it's HIGH or LOW) is determined by using the digitalRead function, which, according to the Arduino documentation, "Reads the value from a specified pin, either HIGH or LOW".

A series of checks are then performed. If the state of switchState is different from the value of lastSwitchState, then we'll check the current state of switchState. If the current state is HIGH, then the switch went from "Off" to "On". The following output would then be written to the serial log:

Serial.print("!state");
Serial.print("1");
Serial.print(";");

Otherwise, the switch state is LOW, and the switch went from "On" to "Off". The following output would then be written to the serial log:

Serial.print("!state");
Serial.print("0");
Serial.print(";");

A delay of 50 milliseconds is added to prevent bouncing. Effectively, we're checking the state of the input twice in a short time to make sure the button is "definitely pressed" (Arduino documentation).

Finally, at the end of the method, we save the lastSwitchState value as that of the current switchState.

Xcode Project

NOTE: Xcode 7.3 is required to run this project. Because it uses CocoaPods, make sure to open the .xcworkspace file, and not the .xcodeproj file.

There are three classes in the app; the Serial Communicator, FMSynth, and the View Controller. The View Controller is responsible both for opening the serial port so communication can occur:

let serialPort = ORSSerialPort(path: "/dev/tty.usbmodem1411")
serialCommunicator.serialPort = serialPort

and, for creating an instance of FMSynth:

let fmSynth = FMSynth()

The FMSynth class specifies the values of the properties that we want to use for our oscillator. AKFMOscillatorhas six properties that can be modified:

    let fmOscillator = AKFMOscillator(
        waveform: AKTable(.Sine),
        baseFrequency: 440,
        carrierMultiplier: 1,
        modulatingMultiplier: 1,
        modulationIndex: 1,
        amplitude: 0.2
    )

These properties are then added to our instrument, and assigned to the instance variables of AKFMOscillator:

    override init() {
        super.init()
        AudioKit.output = fmOscillator
        AudioKit.start()
    }

For this project though, we're just going to control the frequency and modulationIndex properties.

The Serial Communicator calss conforms to the ORSSerialPortDelegate. When serialPortWasOpened is called, three instances ofORSSerialPacketDescriptor are created: one descriptor for each potentiometer, and one descriptor for the switch state. These descriptors specify that we should be listening for a packet that starts with the string values we logged in our Arduino sketch:

let descriptorPotOne = ORSSerialPacketDescriptor(prefixString: "!pos1",
	suffixString: ";",
maximumPacketLength:9,
	userInfo: SerialPortPacketType.PotentiometerOne.rawValue)
let descriptorPotTwo = ORSSerialPacketDescriptor(prefixString: "!pos2",
	suffixString: ";",
	maximumPacketLength:9,
	userInfo: SerialPortPacketType.PotentiometerTwo.rawValue)
let descriptorState = ORSSerialPacketDescriptor(prefixString: "!state",
	suffixString: ";",
	maximumPacketLength:9,
  userInfo: SerialPortPacketType.State.rawValue)

The app then begins "listening" for packets that match the correct description:

serialPort.startListeningForPacketsMatchingDescriptor(descriptorPotOne)
serialPort.startListeningForPacketsMatchingDescriptor(descriptorPotTwo)
serialPort.startListeningForPacketsMatchingDescriptor(descriptorState)

The didReceivePacket delegate method posts a notification whenever a new potentiometer value or switch-state is detected:

	func serialPort(serialPort: ORSSerialPort, didReceivePacket packetData: NSData, matchingDescriptor descriptor: ORSSerialPacketDescriptor) {
		let packetType = SerialPortPacketType(rawValue: descriptor.userInfo as! Int)!
		switch packetType {
		case .PotentiometerOne:
			self.potentiometerOneValue = self.potentiometerFromResponsePacket(packetData)
            NSNotificationCenter.defaultCenter().postNotificationName("PotentiometerOneChanged", object: self.potentiometerOneValue)
		case .PotentiometerTwo:
			self.potentiometerTwoValue = self.potentiometerFromResponsePacket(packetData)
            NSNotificationCenter.defaultCenter().postNotificationName("PotentiometerTwoChanged", object: self.potentiometerTwoValue)
		case .State:
			self.switchState = self.switchStateFromResponsePacket(packetData)
            NSNotificationCenter.defaultCenter().postNotificationName("SwitchStateChanged", object: self.switchState)
		}
	}

Inside of our ViewController's viewDidLoad method, observers for these notifications are added. Whenever a notification is received, it means that our app has received either a new potentiometer value or swtich state from our Arduino sketch:

NSNotificationCenter.defaultCenter().addObserver(self, selector: "potOneValueChanged:", name:"PotentiometerOneChanged", object: nil)
NSNotificationCenter.defaultCenter().addObserver(self, selector: "potTwoValueChanged:", name:"PotentiometerTwoChanged", object: nil)
NSNotificationCenter.defaultCenter().addObserver(self, selector: "switchStateChanged:", name:"SwitchStateChanged", object: nil)

Depending on which potentiometer value has changed, one of the two methods below are called:

    func potOneValueChanged(notification: NSNotification){
        fmSynth.fmOscillator.baseFrequency = Double(serialCommunicator.potentiometerOneValue * 4)
        self.frequencyLabel.stringValue = "\(fmSynth.fmOscillator.baseFrequency)"
        self.frequencySlider.floatValue = Float(fmSynth.fmOscillator.baseFrequency)
    }
    
    func potTwoValueChanged(notification: NSNotification){
        fmSynth.fmOscillator.modulationIndex = Double(serialCommunicator.potentiometerTwoValue / 4)
        self.modulationIndexLabel.stringValue = "\(fmSynth.fmOscillator.modulationIndex)"
        self.modulationIndexSlider.floatValue = Float(fmSynth.fmOscillator.modulationIndex)
    }

Those methods set the value of the oscillator's frequency and modulation parameters, as well as display the values in two labels in the user-interface.

If a notification is received that the switch-state has changed, the method below is called:

    func switchStateChanged(notification: NSNotification){
        if serialCommunicator.switchState == true {
            fmSynth.startSound()
            self.statusLabel.stringValue = "Stop"
        } else {
            fmSynth.stopSound()
            self.statusLabel.stringValue = "Play Sound"
        }
    }

If the switch is in an "On" state, then the oscillator's note is played, and text is updated in another label. If the switch is in an "Off" state, then the note is stopped, and the label is updated appropriately.

The UI is shown below:

Attribution The sound synthesis is implemented through AudioKit, an open- source audio analysis, synthesis, and processing library for iOS and OS X. This project uses AudioKit 3.5.

The OS X app makes use of the ORSSerialPort library.

Thanks to Andrew Madsen for answering questions regarding the library.

This project is licensed under the MIT License.

Contact Info

Email: nicholasarner (at) gmail.com

Website: www.nickarner.com

Twitter: @nickarner

narner/Arduino-AudioKitOSX

Arduino-AudioKitOSX Demo Project

Overview

Arduino Sketch

Xcode Project

Contact Info