Unfortunately, I have yet to solve the circuit issue. However, I’ve been trying many different things to try to figure out what’s wrong.
The first thing I did was test my electrode adapters and my battery connection leads. Both registered as normal as per the multimeter, so I’m confident that it isn’t a soldering or resistance issue due to the length of the battery wires. I also tested my electrodes by themselves, to make sure it wasn’t just faulty electrodes causing the problem, but they also seemed fine.
I also tested my battery voltage, but there was not issue there too. They read right around 9V, as is expected.
Sometime very important that I did figure out is what the black wire all the way to the right of the photo layout is.
The first time I tested my circuit with my laptop, I noticed that that wire had gotten warm. I had questioned why the wire was there before, and I didn’t understand why, but I figured I could remove it if need be. Originally, with the way I had the batteries plugged in (positive and negative leads in the “correct” power strips on top, but reversed on the bottom), that wire connected the two negative leads of the batteries together, such that the current was just intersecting within that wire, which make sense as to why it got hot. After doing some research, I finally figured out that the batteries actually had to be plugged in in a very unique way, which is something the original Instructable did not explain very thoroughly.
However, this Instructable did.
Basically, the circuit only needs three inputs: 9V, 0V (ground), and -9V. The reason we need negative voltage is because the op-amps function from a positive to a negative range of voltage, which in this case is 9V to -9V. This prevents the clipping of signals lower than 0V. We get 0V by combining a negative lead with a positive lead, and then that right-most wire transfers the ground from one power strip where it’s plugged in to the bottom.
After some consideration, I’ve decided to scrap the idea of printing a custom box to house the circuits in. I’m still going to house the circuits, but instead I’ve opted to purchase a simple wooden box with a hinged lid. My main concerns about the box are the electrodes and batteries. I’m going to need to plug my batteries in each time I begin using the circuit, so they’ll have to be accessible, which I why I’ve decided to go with a hinged lid. This will make it easier to work on plugging them in before sessions. However, my original idea was to have the electrode adapter plugs visible from the top of the box, in order to contain the wires better and make it easier to plug the electrodes in and to remove them. If I plan on keeping this idea, I’ll have to solder much longer wires onto the touchproof electrode adapters in order for them to be able to stay plugged in when I open and close the lid. This will take some playing around with, but I’m excited to figure out a solution to this problem.