Code and article for building an iOS-controlled Bluetooth enabled desk lighting rig.
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Building a Custom iOS-Controlled Lighting System

I recently moved into a new apartment. It's a great place, except for one glaring omission: the built-in desk area has terrible light. I looked online a bit, and discovered that there are excellent LED strip lights that would fit under an overhanging shelf and illuminate the desk beatifully.

But I am an Engineer, and Engineers love to build stuff, even when it's not an especially good idea! I decided the preferable course would be to create my own lighting system. With LEDs that can display custom colors. And make it controlled by iOS.

More expensive, harder to build, and probably won't work as well as a commercial solution? NOW WE'RE TALKING!

Because I've done most of my hobby electronics work on the Arduino, I decided to use one of those as the controller for the project. I'd recently learned about the LightBlue Bean, a super-cool Arduino controller that adds Bluetooth 4.0 to the standard Arduino formula. The Bluetooth support would allow it to easily talk with an iOS or Android phone. (Android support is left as an exercise to the reader, because I don't know how to do it.) The NeoPixel LEDs work well, and since you can wire a ton of them in serial, keep the wiring hassle to a minimum. Because the LEDs won't run long on battery power, a 3v power supply is also needed. ("3v" means "3 volts". Using too few volts to power something will result in it not working; too many will cause it to emit smoke and stop working forever. Matching the required voltage to the supplied voltage is therefore pretty important.)

Here's our parts list:

In addition, since we'll be making an iOS app to control the project, we'll need Xcode and an iPhone. And since we'll be programming the Bean, we'll also need the Arduino IDE and LightBlue's Bean Loader software.

Step 1: Wire Up the Parts

We don't want to have to be replacing batteries all the time, so an external power supply seems the way to go. There's one potentially tricky problem here: the NeoPixel strip runs at 5v, and the Bean runs at 3.3v. Fortunately, per "Powering the NeoPixel", "Lower voltages are always acceptable, with the caveat that the LEDs will be slightly dimmer." Dimmer is OK; having our project catch fire and burn the apartment to the ground (which would probably ensure I wouldn't get my damage deposit back) is not. Thus, we'll use a 3v external supply.

We'll also put another safety measure in place: a 1000Ω resistor between the control board and the strip's data pin. (The NeoPixel folks recommend 300-500Ω, but I didn't have one in that range, and the higher resistance does no harm.)

With all that in mind, here's what our final wiring diagram ends up looking like (note -- Safari doesn't render this SVG well. If you can't see the Bean in the diagram, click on it to display it by itself, which appears to fix the rendering problem):

Wiring Diagram

Step 2: The Arduino Software

(Note: you can download the completed software for this project from GitHub.) In order to build the code, you'll need both the LightBlue extensions to the IDE to support the bean and the NeoPixel Library to allow the bean to talk to the LED strip.

The Bean's software supports communicating over Bluetooth two different ways: using a virtual wireless serial port (already familiar to anyone who has done much Arduino work), and through five "Scratch" Bluetooth Low Energy characteristics. Each of these is a 20 byte section of memory, the values of which can be set and read through standard Bluetooth LE protocols.

Scratch Characteristics 1 through 5

For our project, we'll need to communicate four bytes of information: the on/off status for the light strip, and a byte each for red, green and blue color values. Since the payload is small and predictably structured, we'll use the first four bytes of one of the scratch characteristics to store the data:

Sending Data to the Lightblue Bean

Once we've determined how we're going to be receiving the data on the Bean, the main loop becomes straightforward:

void loop() 
  ScratchData thisScratch = 

  if ( thisScratch.length >= 4 ) {
    bool isOn =[0];
    int r =[1];
    int g =[2];
    int b =[3];

    updateLight( isOn, r, g, b ); // more on this in a minute



In the first line, we use the Bean library to read the data from the frist Scratch area. After verifying the we have enough data to break apart, we extract the values for whether the light should be on and each of the color channels and then pass them off to a yet-to-be-written routine for updating our lights. Finally, we use the Bean library's sleep command to put the controller to sleep for one second. (The Bean library's sleep command puts the microcontroller into "deep sleep" mode, and is more power-efficient than the standard one.)

void updateLight( bool isOn, int r, int g, int b ) {
  uint32_t c = strip.Color( r, g, b );
  if ( isOn ) {
    colorWipe( c, 50 );
  else {
    colorWipe( strip.Color( 0, 0, 0 ), 50 );

// Fill the dots one after the other with a color
void colorWipe(uint32_t c, uint8_t wait) {
  for( uint16_t i=0; i<strip.numPixels(); i++ ) {
    strip.setPixelColor( i, c );;
    delay( wait );

In our next section of code, we have an updateLight method that either sets all the lights on the NeoPixel strip to the specified color or turns them all off. In order to have the lights appear sequentially, rather than all at once, we borrow the colorWipe method from some of the sample code that is provided with the NeoPixels. (This is, of course, just for a bit of sci-fi flair -- we could easily have them all come on at once.)

Step 3: The iOS Software

Since we're going for maximum engineering nerdiness, it would be silly not to write our own custom software to control the project. The only UI we'll need for this is a way to select a Bean, an on/off switch, and a way to specify the color:

Bean PickerLight Controls

We'll also include the LightBlue Bean's iOS/OS X SDK, which makes working with the Bean a little easier. Since we are using Bluetooth characteristics to send our data, we could also simply use CoreBluetooth. Including the SDK, however, gives us the flexibility to also take advantage of the Bean's serial connection in the future if we want to.

The Browser Screen

When the browser for available Beans appears, we use the Bean library to scan for available devices:

- (void)viewDidLoad {
    [super viewDidLoad];
    self.beanManager = [[PTDBeanManager alloc] initWithDelegate:self];

-(void)viewDidAppear:(BOOL)animated {
    // call will fail if we don't give Bluetooth a bit of time to spin up
    dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(1 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
        NSError *error;
        if ( self.currentBean != nil ) {
            [self.beanManager disconnectBean:self.currentBean error:nil];
            self.currentBean = nil;
        self.beanArray = [NSMutableArray array];
        [self.tableView reloadData];
        [self.beanManager startScanningForBeans_error:&error];
        if ( error != nil ) {
            NSLog(@"Error scanning for beans: %@", error );

Note one potential pitfall: when we create a PTDBeanManager, we have to give it a little bit of time to get the Bluetooth radio online -- otherwise scanning will fail with an error.

When the Bean manager calls our delegate method to indicate that it found a Bean, we simply add it to our array and update the table to reflect the new device:

-(void)beanManager:(PTDBeanManager *)beanManager didDiscoverBean:(PTDBean *)bean error:(NSError *)error {
    [self.beanArray addObject:bean];
    [self.tableView reloadData];

If the user taps a bean to select it, we then try to establish a connection:

-(void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath {
    PTDBean *bean = [self.beanArray objectAtIndex:indexPath.row];
    [self.beanManager connectToBean:bean error:nil];
    NSLog(@"Connecting to bean: %@",;

And when the connection is made, we finally initiate the segue to show the controls for the bean:

-(void)beanManager:(PTDBeanManager *)beanManager didConnectBean:(PTDBean *)bean error:(NSError *)error {
    [self performSegueWithIdentifier:@"showBeanSegue" sender:nil];

- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {
    PTDBean *bean = [self.beanArray objectAtIndex:self.tableView.indexPathForSelectedRow.row];
    BeanViewController *beanViewController = [segue destinationViewController];
    beanViewController.bean = bean;

The Control Screen

Most of the control panel code just deals with UI. The interesting methods allow us to send an update, with a little bit of data massaging, to the Bean. (ColorSwatchView is simply a UIView. We use the background color to store and display the current color selected.)

- (IBAction)didTapSwitch:(UISwitch*)sender {
    [self sendUpdateToBean];

- (IBAction)sliderDragCompleted:(UISlider *)sender {
    [self sendUpdateToBean];

- (void)sendUpdateToBean {
    CGFloat red;
    CGFloat green;
    CGFloat blue;
    CGFloat alpha;
    [self.colorSwatchView.backgroundColor getRed:&red green:&green blue:&blue alpha:&alpha];

    Byte redByte = floor( red * 255 );
    Byte greenByte = floor( green * 255 );
    Byte blueByte = floor( blue * 255 );

    Byte dataArray[4];
    dataArray[0] = self.onOffSwitch.on;
    dataArray[1] = redByte;
    dataArray[2] = greenByte;
    dataArray[3] = blueByte;

    NSData *payload = [NSData dataWithBytes:dataArray length:sizeof(dataArray)];
    [self.bean setScratchBank:1 data:payload];

We also read the data from the bean when we display the screen to set the status of the UI appropriately:

- (void)viewDidLoad {
    [super viewDidLoad];
    self.bean.delegate = self;
    [self.bean readScratchBank:1];

- (void)bean:(PTDBean *)bean didUpdateScratchBank:(NSInteger)bank data:(NSData *)data {
    Byte dataArray[4];
    [data getBytes:&dataArray length:4];

    BOOL isOn = dataArray[0];
    Byte redByte = dataArray[1];
    Byte greenByte = dataArray[2];
    Byte blueByte = dataArray[3];

    CGFloat red = redByte / 255.0;
    CGFloat green = greenByte / 255.0;
    CGFloat blue = blueByte / 255.0;

    UIColor *color = [UIColor colorWithRed:red green:green blue:blue alpha:1];

    self.onOffSwitch.on = isOn;

    self.colorSwatchView.backgroundColor = color;

    self.redSlider.value = red;
    self.greenSlider.value = green;
    self.blueSlider.value = blue;

With all this code in place, we can finally send updates to our completed light system!

Step 4: Profit?

This is almost certainly not a practical lighting system for everyone, but for folks with an inclination toward tinkering, it opens up lots of interesting possibilities for customization and improvement. It would be easy to add a variety of animation effects when changing the light's color. One could monitor the Bean's accelerometers so that you can turn the light on and off by thumping the shelf it's mounted under with your fist (I call this "Fonzie mode"). The lighting could be automatically adjusted to be more blue in the morning to help you wake up, and more red in the evening so as not to interfere with your sleep, a la Flux. And of course one could tie it into various web services to provide quick information on weather, the stock market, etc.

The project was great for learning better how to control hardware from iOS, and should be a fun build for anyone interested in that sort of integration. If you decide to give it a try, feel free to email me at if you bump into any issues, or if you have suggestions or code improvements. I'd be glad to hear from you!