Inexpensive EEG Devices?

Rustcycle akss: "To extend prior music generation experimentation, I'm interested in creating music via genetic algorithms using neurofeedback to assign fitness values. Does anyone have a recommendation for EEG systems that are affordable outside research institutions? What's the best system under $2k? Ideally I'd want a multi-sensor system so I could do sonification experiments to 'hear' correlated data from different regions, but I'd settle for a one or two sensor system for initial experimentation — so long as there are drivers for Mac / Linux. How safe / unsafe is the OpenEEG route?"

Comments

Homebrew

[DrLang21]

Under $2000? I would be surprised if there was a system that cheap. I think your best bet is to build you own differential amplifiers with a couple of opamps.

Re:Homebrew

[smellsofbikes]

Instrumentation amplifiers. They're cheap and astounding. CMRR's of 80 or 100. Take a look at the Analog Designs AD620, for instance. It's superb (even if they are our competitors.) I've used it for making an EKG based on an old Scientific American Amateur Scientist article, and here's a slashdot thread about another AD620-based EKG.

This system is dirt cheap

[Centurix]

1. Buy 2 kilos of sugar and a hand-held Casio keyboard.
2. Eat sugar
3. Compose like your hands are on fire.

You need enough sugar floating around so that if you ever take a PET Scan, your brain would show up a sort of platinum white colour on the screen.

Re:This system is dirt cheap

[lisaparratt]

"Sugar", eh?

Re:This system is dirt cheap

[Centurix]

I subscribe to the Jan Hammer school of Sugar composing. The 80's have never been so alive.

The Casio is interchangable with a Keytar.

Re:This system is dirt cheap

[ceoyoyo]

Hm... you didn't mention it has to be RADIOACTIVE sugar.

That depends

[nizo]

How safe / unsafe is the OpenEEG route?

That depends, how comfortable are you drilling holes into your own skull?

OpenEEG

[Anonymous Coward]

My senior design team from College actually went ahead and tried to build the machine featured on OpenEEG. In my experience, we were not capable of getting a signal with a high enough resolution of detecting anything other than "ACTIVE" or "NOT-SO-ACTIVE". But the circuitry provided does ..work... after a bit of tinkering. The resistor values are very important. Try to be as exact as possible. Also, shield everything you can from inteference. You'd be surprised how much interference the power lines in your house emit. It will be about around 60Hz, and periodic, if you are picking it up. The DRL portion of the circuit helps to reduce it.

As for analyzing the data it produces, that also becomes difficult. "ACtivity" on an EEG signal could be as small as a uV. Sample it as fast as you can. We used a PIC processor to sample.

Also, muscle signals can drown out the electrodes, try not to move.

Re:OpenEEG

[tibike77]

Or, you know, you could try to get your hands on some "vintage" oscilloscopes (should be dirt-cheap) and use THEM as basis for your "machine".
As a kid, I had more than my fair share of fun with some pretty old ('70s or so) osci's at my dad's workplace (electrical engineering).

Re:OpenEEG

[ceoyoyo]

When I was in high school I tried to build an EEG system. I started by looking at the heart -- ECG signals are about a thousand times higher voltage than EEG. Even a vacuum tube scope couldn't pick them up though, and certainly couldn't register anything through the 60 Hz hash.

EEG and ECG use some pretty clever tricks to actually get a signal. One of them is taking the difference between electrodes placed on the heart or head and one placed on an extremity.

Re:OpenEEG

[ChrisMaple]

I think Tektronix made a very sensitive differential amplifier for one of their plugin oscilloscope systems. This might work, but it's not really the best approach. If you have electrical engineering abilities, make a good low frequency differential amp. Chop the output and feed it into the audio input of your computer. Use software to demodulate the chopped signal. (If your audio card has good response down to about 1/4 Hz, skip the chop/demod steps). You now have data on the computer that can be displayed, printed out, or analysed. Costs could be below $30, but there's a fair amount of software and hardware design and construction involved.

Maybe back issues of electronics magazines?

[badfish99]

I remember seeing several designs for this sort of thing back in the 70s or 80s in electronics magazines for hobbyists. I've no idea whether they worked, but it might be worth asking you local library if they have back issues from that long ago (it was pre-world-wide-web, obviously).

I think people used to hook them up to lights and then smoke weed and admire the pretty patterns...

Re:Maybe back issues of electronics magazines?

[danlyke]

Steve Ciarcia did a system back in the '80s in Byte magazine that I remember primarily because I was reading through it and thought "why's he using batteries and doing so much work to isolate this side of the board from the other?", and then realized the possible problems that could stem from power supply failure or getting RS-232 voltages on to the probe side of the board. But whenever I go back to those old circuits I'm shocked by the complexity of the designs, mostly because we now have a much better array of integrated circuits and complete devices.

I've looked at the OpenEEG circuit a bit, and while my hardware experience is limited to building things like stepper motor drivers I've considered building it and hooking it up to myself. If you have trouble with the analog side of the board you might try looking around in the old-school guitarists in your area; I've found a number of guys who played back in the '70s who got really good at analog electronics and noise shielding because they got into building their own pre-amps.

And as others in this thread and elsewhere have said, once you build the hardware you've done the easy parts. You're looking for fairly small low frequency signals in a world full of very big low frequency signals. So put a value on your time and know that a lot of what you'll be doing is signal processing on a bigger CPU, not just using a microcontroller to feed small measurements to that big CPU.

Re:Maybe back issues of electronics magazines?

[cr0sh]

Steve Ciarcia did a system back in the '80s in Byte magazine that I remember primarily...then realized the possible problems that could stem from power supply failure or getting RS-232 voltages on to the probe side of the board

This can't be stressed enough, which is why you will often see "not for medical use" disclaimers on the el-cheapo (comparitively) EEG devices out there. I have a copy of that article (somewhere - maybe one day I will stick it up on my website), and from what I remember, it was nothing more than a special very high gain op-amp. It was originally designed for medical grade devices (which is why it was so expensive even then), and had its own internal isolation. Steve added further isolation external to the device for further protection.

Think about it: you are putting probes on your body with low-resistivity conductive gel, generally on the head or on other areas to read neurologically-based voltage signals. What can flow one way can flow the other, and if your isolation is wrong in any way, you can easily electrocute, and kill or maim yourself. Properly designed and used, these devices can be relatively safe, but always be aware of just what it is you are doing.

Also, be aware that you likely can't just cascade a bunch of op-amps together with their gain signal left open (thus, "infinite" gain) - what you are fighting against (and you hint at) is noise, and el-cheapo op-amps are going to have a ton of it, which was another reason why Steve used a commercial graded medical op-amp, to keep the noise from the electronics down. However, even then you will be left with a signal that is very noisy, and requires a ton of filtering to get anything useful out of it...

Re:Maybe back issues of electronics magazines?

[Amadodd]

I remember Garcia and actually built that ECG circuit back in '87 or so. Didn't have money for the opto-isolators, so i wired it directly to my A/D convertor that was in turn connected directly to my ZX Spectrum. Still used a seperate battery for power, but everything had basically the same ground circuit. I never got any real shocks, just some tingles once or twice, but the fact that it was not completely isolated caused a lot of 50Hz feedback. I had to use a lot of clock cycles in code to clean up the waveform to make it look anything like an ECG.
Those were the days.

A Friend of Mine

[TubeSteak]

A friend of mine bought a EEg for neurofeedback... but the sucker didn't come with any drivers, disks or manual.

And he can't find anything on the internet that is useful to get it working.

So, be careful what you buy, because you might just get a hunk of hardware, but no software to run it.. if you're going the cheap route that is.

Re:A Friend of Mine

[MikeFM]

Some years ago I bought a unit from an ad in Circuit Cellar Inc magazine that worked reasonable well given it's very low cost. It had dos drivers that didn't do much more than interface with their custom program for displaying the output but we were able to write our own drivers without to much pain. Maybe your friend could do the same?

EEG options

[arcmay]

Colorado State University was/is doing some work with EEG. Their project website lists the products they use, which seem to be in your price range.

Sounds familiar...

[tomzyk]

I think this is along the same route that The Bloodhound Gang (the band, not the TV show) used for writing "A Lap Dance Is So Much Better When the Stripper is Crying".

Re:beware of licensing issues...

[Twixter]

...before you link the electrodes to your head, as you wouldn't want to be contaminated by GPL and have to release all your dirty little secrets! Then they will all know how paranoid you are!

Mindset

[sg]

Depending on the channel density you need, you might want to look at Mindset from NeuroPulse-Systems. The 16-channel unit is somewhat close to your price range.

DON"T TRY THIS AT HOME

[MountainLogic]

Seriously, the subject MUST have full galvanic isolation from the power lines. The reason for this is that in every day life your skin provides a surprising amount of resistance and thus protection from shock. What is safe, 48 VDC, can kill an electrically compromised subject. When you put electrodes on the skin you create a low impedance path into the body. The typical solution for this is to use optical isolation. Check out Dallas/Maxim Semi and others for off the shelf solutions. DO NOT hook someone up to an oscilloscope - one leak in a transformer and they are dead. The other solution is to use batteries, but you have to be careful to limit the available voltage and current from a battery source.

Re:DON"T TRY THIS AT HOME

[backwardMechanic]

It's not difficult to do, but you're right, it is critical. Use batteries - it's safer, easier and gives a very clean power supply. Opto-isolate, to protect yourself, and to protect your PC from cockups. I haven't seen a nice USB to digital-over-fiber box, but one must exist - has anyone out there found one?

Re:DON"T TRY THIS AT HOME

[Steve1952]

This is good advice. Pay attention! (I have a biophysics background as well.)

Store down the street

[Unknown_monkey]

The Super Wal-Mart has EGGs in packs of 12 for like US$0.97.

Do you need to own it?

[Iron Condor]

It's not clear to me from your articles whether you actually need ownership. This sounds like the kind of thing you might be able to get some gradstudent at the next medical college interested in. Voila: access to reasonably good and usually well-maintained equipment. Maybe someone is going to get a seniors thesis out of it. Heck, there may even be a way to get some small internal tech-development grant or some such to cover operational costs.

You don't think you're the first one to think of this, right? Heck, there may even be literature left behind from one or a couple other folks who've tried similar things in the past.

My personal experience in the past has been that it is smarter and cheaper to befriend an astronomy grad student for access to some real telescope than spending thousands on buying your own (which will never hold up quality-wise). I can't quite see why this shouldn't hold true for medical equipment as well.

Thanks!

[rustcycle]

Thanks for the ideas and leads...will have to check out CSU up the road - between Darrell Whitley and the EEG work that's two compelling reasons to make the drive for collaboration :-)