From: Doug Sutherland (wearable_at_earthlink.net)
Date: 2001-12-13 01:17:49
Hi Theron,
> Recently I purchased an older EEG machine TECA 1A97A for
> a very reasonable price.
Interesting. I've been noticing some cheap older used EEGs
at sites like these:
http://www.brainwavetx.com/tech/nt/
http://www.pemed.com/neuro/neuro.htm
> What I'd like to do is some how interface with the machine
> so as to do monitoring on my pc rather than the paper/pen output.
>
> so my question is two fold.
>
> 1. Has anyone here done such a thing with an older machine.
I haven't done whis with EEGs, but I bought a bunch of cheap
industrial instrumentation hardware on ebay and have been
able to interface some of it to PCs. Most industrial and
medical devices have either an RS232 serial port or analog
outputs. Here are some ideas:
1) Check to see if there is an RS232 serial port on that
machine (DB9 or DB25 connector). If there is, then there
is a good chance that you can interface it to a PC.
2) Check if the manufacturer is still around. If so, send
them an email and ask:
a) if you can get the manuals
b) if they can tell you the details on the serial port
protocol
I bought an air quality monitor for cheap on ebay and
it had a serial port, but I couldn't figure out how to
get data from the port. I emailed the company and they
told me the protocol info and the magic key to enable
data on the port. In this case the PC had to send a 7
character sequence to enable "real time monitoring"
on the port. After I knew that, it was easy to write
a little driver to grab and parse the data.
3) If there is a serial port but you don't have the info
on its protocol, then you need to experiment. Try
using a serial terminal program like hyperterminal
on windows or minicom on linux. You will need to try
different baud rates and parity settings. With some
devices I have been able to figure out the baud rate
and parity this way, by trial and error.
If you see data arriving in ascii text then you will
be lucky and it might not be hard to figure out. If
the data arrives in binary then you need to write a
little program to aid in figuring out the data stream.
This is what I would do. Write a program that tries
different baud rates and spits the data out into a
console. If it all looks like special chars then its
probably is binary and needs conversion to character
so you can read it.
The data that comes from an EEG is pretty simple, it
is just a bunch of voltages. So it's probably easier
to figure out an EEG data stream than it might be for
other devices. There may be some header info followed
by data. You need to look for patterns. I hope you
have lots of time and patience.
4) If there is no serial port, then there might be
analog ports. These are another way to send the data
to another machine. They will scale the original data
down to a 0-5V range or some other range. The challenge
is figuring out what algorithm they use for scaling so
can revert the data back. This might be harder to
figure out than a serial data stream. I have a device
that does this, it's an infrared spectrophotometer.
The device will scale PPM (parts per million) down
to a 0-5V range and send that out the analog port.
There is a meter on the device with a needle showing
the readings, so I was able to watch the needle and
look at the voltages coming across the analog port
and figure out the scale. You may be able to do the
same if the EEG shows the readings on the device.
You can start with a multimeter and see if you can
figure it out. Of course your PC doesn't have analog
input ports, so you either need to add an ADC card
(ISA or PCI) or used a serial addon ADC capture
device (RS232 or USB) or put a microcontroller in
between the PC serial port and the analog output
port on the EEG.
> 2. If so what software would you recommend me using on my
> pc for monitoring and where can I get this software.
As far as I can tell, there are not many industry
standards for EEG data formats. This throws a loop
into generic software that will work with EEGs. It
seems that most companies have their own proprietary
software. But the data is just voltages and the
techniques for sprectral analysis are pretty much
the same for most devices. The most standard way
to look at the data is using fast fourier transform
(FFT). There are tons of free software sources for
this. See my web page for some sources. Another
possibility is Matlab, it seems like a lot of EEG
researchers use Matlab to look at EEG data.
http://home.earthlink.net/~wearable/biopsy/#dsp-articles
-- Doug
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