Post by thread:[PICLIST] Brainwave monitor

Is there anybody that can help me to design a pic based interface for a brainwave monitor? I need at least a four channel display. It can be for pc or gameboy. I think a dual channel oscilloscope presented in EPE magazine, based in 16F877 can help, but I would like to know how to add more channels. In Elektor was presented a gameboy based oscilloscope, but I have not read it. The analog part is easier for me. Victor -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email spam_OUTlistservTakeThisOuTmitvma.mit.edu with SET PICList DIGEST in the body

At 10:59 AM 6/14/01 -0600, Victor Valdez wrote: >Is there anybody that can help me to design a pic based interface for a >brainwave monitor? I need at least a four channel display. It can be for >pc or gameboy. >I think a dual channel oscilloscope presented in EPE magazine, based in >16F877 can help, but I would like to know how to add more channels. In >Elektor was presented a gameboy based oscilloscope, but I have not read it. > >The analog part is easier for me. >Victor You have a major amount of isolation work to do for anything like this that connects to a line powered device. Serious safety issues. That being said, you need differential amps for the signals, with wide CMRR. A browse through national semi' s web page should let you find some good op-amps to do the job. The most bandwidth you need is only a few hundred Hz, so you can really compromise on speed. Once you have the isolation and analog part worked out, the rest becomes ADC and output issues. -- Dave's Engineering Page: http://www.dvanhorn.org I would have a link to http://www.findu.com/cgi-bin/find.cgi?KC6ETE-9 here in my signature line, but due to the inability of sysadmins at TELOCITY to differentiate a signature line from the text of an email, I am forbidden to have it. -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email .....listservKILLspam@spam@mitvma.mit.edu with SET PICList DIGEST in the body

Dave Van Horn wrote: >At 10:59 AM 6/14/01 -0600, Victor Valdez wrote: >>Is there anybody that can help me to design a pic based interface for a >>brainwave monitor? I need at least a four channel display. It can be for >>pc or gameboy. ........ >You have a major amount of isolation work to do for anything like this that >connects to a line powered device. Serious safety issues. > >That being said, you need differential amps for the signals, with wide CMRR. >A browse through national semi' s web page should let you find some good >op-amps to do the job. >The most bandwidth you need is only a few hundred Hz, so you can really >compromise on speed. > Victor, EEG signals are very small, in the 5-100 uV range. You will need a differential amp, a low-pass filter, very good electrodes, and a well-filtered power supply, in addition to isolation as Dave said. Anything you connect to the body has the definite possibility of shock hazard, so this should be your first concern. Running your amps off batteries and feeding to a gameboy or battery operated notebook is a good idea. The amp should have the highest CMRR possible and preferably be battery run. 60 [or 50] hz pickup from the mains is a big problem with this type of recording, due to the low signal levels. You should try to put a lot of gain in the headstage, as opposed to downstream, because this usually results in less overall noise. You can use a "driven shield" on the electrode wires. You also need a very good ground/reference lead on the scalp, located near the recording electrodes. It's exact placement has a lot to do with the type of recordings you end up with, and you might do some research on what is called the "10-20" EEG arrangement. The electrodes should be high quality silver/etc, and contact made using conductive gel. They should be taped down firmed to prevent movement artifacts. The technicians usually clean the oils off of, and rough up the scalp surface a little, to get good contact. If you head is covered with a bunch of tiny little welts afterwards, the technicians know they did their job correctly. The headstage needs some kind of AC-coupling in order to reject the contact potential of the electrodes. You have uV level signals riding on a time-varying contact potential that is on the order of 0.5-0.7v. Plenty to think about, good luck, - dan michaels http://www.oricomtech.com ========================== -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listservKILLspammitvma.mit.edu with SET PICList DIGEST in the body

>AM modulator This will work but it requires a lot of work. In fact using FM is much easier. One uses the input signal after some DC amplification to provide frequency deviation in a simple FM transmitter and listens in a commercial receiver. Since the FM transmitter has microphone level input sensitivity the required dc gain is only of 100 or so. Galvanic separation and wireless transmission are solved at the same time. Turn off AFC in the receiver. Once upon a time there was a biofeedback scheme based on this I think. It used an extra audio subcarrier and a modulator in the transmitter. Peter -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads