Circuit Cellar HAL-4 4-channel EEG
jct4764
California
I built a HAL-4 EEG from a kit in 1989. It was a complicated build that required a lot of soldering, but it worked great. The only issue I had with it was that it was very sensitive to muscle twitching, so you had to sit very still while using it to get good data. I haven't used it in more than 20 years. I'm thinking about trying to revive it. I still have the Technical Manual , and printouts of the software source code that I wrote to use it with an Apple Macintosh. Does anyone else have experience with the HAL-4? Does anyone have any advice on reviving it? Is there any chance of making it compatible with OpenBCI software?
Comments
Hi JCT,
Wow, Steve Ciarcia's Circuit Cellar column in BYTE Magazine. Brings back memories. Steve's page on Wikipedia:
https://en.wikipedia.org/wiki/Steve_Ciarcia
He's still publishing!
https://circuitcellar.com/
Your device appears to send out a serial byte stream at 4800 bps. Likely if you wrote to Steve, he could send you the data format. With that info (and any commands needed to start / stop / etc, the data stream), you could parse the stream yourself.
It's unclear from the description, if he is sending the raw samples (at unspecified sample rate), OR, he could just be sending the FFT result as shown on the screen shot. My guess since the baud rate is so slow, it's the latter. If that is the case, then that precludes doing any other signal processing on the raw EEG.
Regards, William
Actually on closer look, I think Steve sold the magazine. So others are now running Circuit Cellar.
https://circuitcellar.com/cc-blog/ciarcia-onward-upward/
The FFT wasn't done on the board; it was done in the software that came with the kit. I'd really love to take a look at that software, but it is on a 5 1/4" floppy disk. It's been many years since I've seen a drive that could read it. The software that came with the board was for an IBM PC, and I only had a Macintosh at the time, so I wrote my own FFT.
If that is the case, and you wrote your own FFT, then you must know the format in which the HAL-4 is sending samples:
So you should be able to write programs in the language of your choice, to do whatever signal processing you want to do. There are libraries now for DSP such as:
https://www.google.com/search?q=python+dsp+library
https://www.google.com/search?q=python+parse+serial+data
While it is 'possible' to hook up your device to the Brainflow framework, and then in turn to the OpenBCI_GUI, I would not recommend that route because it is quite complex.
https://brainflow.org/
Regards, William
I knew the HAL-4 format 32 years ago when I wrote the FFT software. The manual doesn't have detailed information on the format; that's on the 5 1/4" floppy. I don't have the computer or disks from then. All I have is some printouts of my assembly language code. That should be enough to figure out the format, but it would be a pain in the butt. I've been looking at the OpenBCI hardware and software, and it looks much more capable than what I had back then, and it would certainly be easier. I think I might get a Ganglion board. I think it will be more than good enough to test the brain wave entrainment device I'm building.
Ganglion would be a good upgrade from the HAL-4. Most likely the HAL had a sample rate on the low range of what is typical now. Using OpenBCI will also let you use the GUI and a whole range of other analysis apps.
https://docs.openbci.com/docs/06Software/SoftwareLanding
re: brainwave entrainment
There are various ways this is done. Lights or sound flashing / drumming at the desired frequency will produce some EEG in the occipital (or temporal) area. Some commercial devices use 'binaural beats', which are said to work, but may not produce an EEG signal:
https://www.autodidacts.io/binaural-beat-openbci-eeg-experiment/
https://neurobb.com/t/anyone-have-experience-with-binaural-beats/80/35
Some very sophisticated BCI open source software, allows the creation of a 'speller', using cVEP code based visual evoked potentials.
https://mindaffect-bci.readthedocs.io/en/latest/
Older VEP paradigms focused on SSVEP, steady state VEP.
Regards, William
I built a binaural beat generator in 1988 and later tested it with my HAL-4. It didn't have much effect on my EEG. The HAL-4 showed that flickering LED goggles worked much better. The device I'm working on now will have flickering LED goggles and generate isochronic tones, which are said to be more effective than binaural beats. There are commercial products similar to this, but building my own will let me try out some ideas for brain wave entrainment that I can't try with commercial products.
Thanks for the link to MindAffect. I think I might have a use for that and I'll look into it.