EEG sensors

I am thinking of building a brain computer interface device and am not sure how to go about this. I need a sensor that reads brainwaves and transmits them to the arduino. I found these expensive devices that can be bought can hacked to get the sensors and chips out. But does anyone know some cheap sensors that can get the data from the brain? It need not be all that much sophisticated. Even if I could get the most basic device that basically does something based on signals from your brain, I would be happy. Please help!!

Have you looked into Mindwave EEG Headsets | NeuroSky Store ? I have seen some Arduino projects using that.

Anantha:
But does anyone know some cheap sensors that can get the data from the brain?

There's no such animal. Some fairly sophisticated amplification, filtering and processing is required to get even the most basic brainwave data.

As suggested by lmrudner, the Neurosky headsets, or even the Mattel Mindflex headsets, can be hacked to extract the data.
I used a Mattel Mindflex headset, to keep costs as low as possible.
(Both use the Neurosky TGAM1 chip.)

If you do a thorough search, there's plenty of info available on the web.

As a starter, take a look here:-
How to hack toy EEGs

See this thread:
Is it safe to connect Arduino to human body?

Archibald:
See this thread:
Is it safe to connect Arduino to human body?

You raise a good point.

Most of the Mindflex/Neurosky hacking articles that I've read, (including the one I linked to), have pointed out that it's not wise to connect directly to a PC via USB. (A laptop is OK, if the charger isn't connected, of course.)
The Neurosky headsets use Bluetooth comms, so there's no problem. You just use, (or hack), the receiving Bluetooth dongle.

The Mindflex headsets also use RF, but it's proprietary and hard to hack, so the simplest safe option, (and the method that most people use), is an RF transmitter module powered by and attached to the headset. I used an APC220 serial 433MHz module for my setup. The TGAM1 chip's data is standard serial at 9600 baud, so it's easy to connect to a serial RF module.

It's not worth risking a zap of high voltage from a faulty/poorly designed PC USB interface/PSU.

If the setup will only be used when connected to a battery-powered Arduino (without a PC), it's perfectly safe. No one ever died from low-voltage DC, as far as I'm aware.

OldSteve:
It's not worth risking a zap of high voltage from a faulty/poorly designed PC USB interface/PSU.

Consider a short between live and earth occurring elsewhere on the electrical power distribution. I wouldn't want a low-resistance electrode on my head connected to earth when that happens.

Archibald:
Consider a short between live and earth occurring elsewhere on the electrical power distribution. I wouldn't want a low-resistance electrode on my head connected to ground when that happens.

True. As I mentioned, the best way to avoid anything like that is to keep the headset totally isolated using RF comms powered by the headset's batteries.
There's no need for any direct connection whatsoever, plus there's more freedom-of-movement using RF.
It's no more dangerous than the original Mattel Mindflex game itself.

Edit: Here's a pic:-

OldSteve:
Edit: Here's a pic:-

I have almost the same thing. I used a XBee.

DuaneDegn:
I have almost the same thing. I used a XBee.

I've been meaning to get back onto that project for a while, but keep getting side-tracked.
Are you using the "Brain" library?

@Anantha, if you do go the Mattel Mindflex route, that library is pretty handy.
It's available here:-
Arduino Brain Library

The measurement is tricky because its a small signal with high impedance drowned out by all the mains-borne
noise in the environment. You want battery powered simply to filter out a lot of the mains interference
anyway (the sensor unit floats at the same potential as the user). Remember you want millivolt level
signals and ambient mains electric fields in buildings are in the 10--100V range.

Also laptop screens put out tonnes of interference too - its an education just to wave a scope-probe round a
room and see how much electromagnetic junk is around.

Take the easy route and use a known working sensor (unless you enjoy challenges!)

OldSteve:
Are you using the "Brain" library?

I haven't used mine with an Arduino yet. I used a Propeller microcontroller.

DuaneDegn:
I haven't used mine with an Arduino yet. I used a Propeller microcontroller.

I used a PIC initially and parsed the TGAM1 data myself, but then switched to the "Brain" library when I started playing with Arduinos, to avoid doing it all over again the hard way. That's one of the best things about Arduino - the availability of such a wide range of libraries to do all of the legwork.