Per previous posts, I am making some free software available here (although it’s somewhat niche): A Mac OS X Distributed Objects server for the Neurosky brain wave reading Mindset and a Quartz Composer plug-in client for the server. (If you have neither OS X nor the Mindset, you might want to wait for a future post where I talk more about how the brain wave art project is coming.)

This post will also serve as a brief introduction to what it would take for you to write your own Cocoa client for the server. But, If you just want the software, you can get it here:

Notes:

  • To install the client for Quartz Composer, close QC and copy the .plugin file to: “/Library/Graphics/Quartz Composer Plugins”. When you next open QC, you should find it in your Patch Library listed as “MindSetQCClient”.  Usage of the patch should be obvious,
  • The server shouldn’t need to start first as long as the client periodically checks for a vended object, but when troubleshooting it’s probably a good idea to start the server, then the client.
  • The server needs the Thinkgear bundle in same directory as the server app. (I’m not including the Thinkgear bundle, it’s available from the Neurosky website for free as part of their developer stuff.
  • Neurosky documentation has instructions for how to figure out what serial port your mindset is on, iirc.  The default for the server is the one I use.
  • I’ve borrowed so heavily from a hodge-podge of tutorials and examples, that I’m not going to include a license for the code. Use it as you will.

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So, onward to the tutorial/implementation details:

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Distributed Object Mindset Server and Client

This server is intended to be a little easier to use than some of the connection methods Neurosky provides (at least in my mind). It grabs data from the Mindset and provides it to Cocoa client applications (such as my Quartz Composer plug-in) by using Objective-C / Cocoa’s Distributed Objects interprocess messaging capability.

To access the Mindset data, the client must create an NSConnection to “JacksMindsetServer”. This gives it access to a vended object which supports the following very simple protocol (this protocol will have to be included in your client header file):


@protocol PassingMindData

-(int) getDataCount;

-(NSArray *)getOldestData;

-(void)removeOldestData;

@end


Creating the connection to the vended object which uses that protocol is simple and requires only a short bit of code:

if (!sharedObject)

{

NSString *_host = nil;

sharedObject = (id <PassingMindData>)[[NSConnection rootProxyForConnectionWithRegisteredName:@"JacksMindsetServer" host:_host] retain];

}


You should now have an object called “sharedObject” which allows all of the methods specified by the “PassingMindData” protocol created above and which will pass the data from the mindset server to your code. To do so, the primary method is “getOldestData”. Calling this method will return an array of the oldest line of values from the Mindset and getDataCount returns the number of lines currently queued.

The returned array contains ordered NSNumbers representing each type of value available from the mindset. The array elements can always be accessed in the following order:

  • Attention (0)
  • Meditation (1)
  • Raw (2)
  • Delta (3)
  • Theta (4)
  • Alpha1 (5)
  • Alpha2 (6)
  • Beta1 (7)
  • Beta2 (8)
  • Gamma (9)
  • Gamma2 (10)
  • SignalQuality (11)

The client is left to access these elements as it pleases from the NSArray object returned by getOldestData. The server also relies on the client to remove the original data from the server as soon as it grabs it by calling “removeOldestData” on “sharedObject”.  (If the client does not call this, there is no auto-cleanup by the server until it’s stopped or exits and the client will not be able to access new data.)

If multiple lines of data are queued, getOldestData and removeOldestData should be executed repeatedly. A simple example would be:

if ([sharedObject getDataCount] > 0)

{

mindDataLine = [NSArray arrayWithArray:[sharedObject getOldestData]];

[self setOutputAttention:[[mindDataLine objectAtIndex:0] doubleValue]];

[sharedObject removeOldestData];

}

That’s really it.  How to write a server is out of the scope of this post, but Neurosky has some great documentation and have provided examples from which I have –heavily–  borrowed.

Let me know if you have questions or need further explanation. I’m going to continue to work on the art project with this stuff and will post more about that later.

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