The electrodes were the biggest part to the construction of the EEG. We had to create adn etch the boards ourselves from scratch. Someone might stumble upon this blog at some point, so I will try to be detailed in describing the process and problems as well.
For starters we made Pedro Ortega’s active Electrodes, which were going to give us the strongest reading and we wouldnt have to get any electro-gels. We liked this because A. it apparently gave us a better reading than the passive electrodes and B. it gave us the ability to just place the electrodes on the head instead of affixing them to the body with gels, etc.
We had to start collecting all the materials, which was a bit of a treasure hunt for us. There was a lot of things we werent sure about how to get but after several days of hunting, we got the majority of it.
The electrodes needed:
a copper board, etching solution, container for etchant, 4 x 200k (we used 220K and it worked fine), 4 x 10k and 4 x 100Ohm resistors; 8 x 100pF and 4 x 10nF capacitors; 4 x TLC272 opamps; some silver wire of 1mm diameter
So in terms of etching, there are a lot of options out there. We tried to go “green” (literally) and get muriatic acid at the hardware store (~5$) and hydrogen peroxide. It gets mixed in a 2 to 1 solution with the peroxide being the “2″ and the muriatic being the “1″. When you pour it in, it releases a gas (im assuming its CL gas) which can be a little toxic smelling, but dont worry, its only frying a little bit of your brain.
You take the layout for your PCB board (which for us, was conveniently on Pedros site) and print it out on MAGAZINE PAPER (FROM A PAGE, NOT THE COVER). we got confused as it said “polyester paper” so we figured we could use any old fabric made paper (read: cotton) and it didnt work. It needs to be water resistant so the LASER printer (which is also very important) ink sticks to it. The laser printer toner is made from plastic and prevents the board from being etched where it is printed. fairly cool actually.
clean it off with acetone, fyi, when its done. its fast and and you don’t waste your time scrubbing.
Ok, so you need a 1mm drill bit. its a pain in the ass to find one and it needs to fit into a dremel. We found one around the corner from NYU on 8th st at the hardware store next to the world of warcraft place. It takes a pretty steady hand to do it (which I don’t have at all) but luckily we didng break the bit. You have to dripp about 36 holes per board so the process gets tedious.
the easy part, right? no.
The parts need to be SECURELY sodered to the board. then CHECK THEM with a multimeter. This is important. That way, when you go to cover them with silicone/glue them to your helmet/seal them with hot glue/whatever – you know that they work on the board end of things. Also, you will do a lot of soldering wires, so be careful not to overdo the soldering. The copper will come off the board with time.
So this was the trickiest part. Our suggestion: go buy cheap XLR cables at a sound shop in sunset park and haggle with the guy on price. two elctrodes will make one channel. So you ended up soldering an XLR to each electrode, then joining them together with a Y connector, then soldering that XLR to a 3 pin female connector. It gets confusing there, so be careful. ****THIS IS IMPORTANT**** There are 4 connections on the electrode (-, +, an arrow, and a box). The + should be your your power, the “-” should be your ground and should be connected to your SHIELD in your shileded XLR Cables. The arrow should be connected to the other wire in the XLR. the BOX is not connected to anything.