Has been a long time since my last post, almost 8 months.
The very first days of September the first version of the PCB arrived, and it all worked flawlessly (even if the last amplifer stage was designed craply, I'll explain more about it later), it all worked both hardware and software part.
I've been using Eagle for a long time, it was my first ECAD but the time passes and my needs changes, I tried almost any EDA software available, the first one I've tried out was KiCAD, and it's quite impressioning for being an open source software, from this perspective I've liked it, but it didn't meet al my requirements. The second revision of my board was made with KiCAD but unfortunately it didn't work: The last amplifier stage wasn't designed with single supplies in mind, it was a complete mess: the reference wasn't centered at half of the supply and if I swapped the electrodes it saturated in the first version, in this second version the last stage didn't work at all.
School started in september and I was involved in various projects: the city were I attend my courses, Casale Monferrato, is "famous" for being the one were the "Eternit" was made: this material made out of asbestos killed a lot of people in Italy, specially in Casale.
Casale hopefully has been completely cleared since a lot of years, were it used to be the Eternit factory now there's a commemorative park for the victims called "Parco Eternot", when it was opened even the President of the Republic of Italy was present, it was such an important event: it closed one of the worst chapters in the italian history.
But even if Casale is completely cleared, many italian cities aren't, so me and my work team decided to build a robot that sprays some "containing liquid" to prevent workers putting their life at risk (if you're interested here's a link to the introduction video). It was submitted for the Italian Robotics Olympiads and it even was selected for the finals, but we all now what happened in Italy since february: my region, Piedmont, was one of the first to be lock-downed: we don't go to school since the 22nd February, and we almost immediately activated all forms of e-learning available, it's two months now that we do lessons on Google Meet.
This forced quarantine made me pick up this project, and while my work team is thinking out something to help out people in hospitals (we're both Electronics and Mechanics technicians), I'm using my spare time to update this project. Time has passed since the last revision of this project, and obviously I've learned a lot of things in the field, specially in analog electronics. So, after revisiting the old schematics, I've decided to make all over again, it was such a mess that i don't even know how the first revision worked.
So, I don't bother you all anymore with my life and I start talking bout the project, you're here for this, no?
Previously I've talked about ECAD, the last (hopefully) program that I've been using for a while is Cadence Allegro, even if it has an enormous learning curve, is one of the best EDAs I've ever tried, even the inclued simulator, PSpice, is way better than any tools I've been using, Multisim in primis and LTSpice.
The last revision is now functional in breadboard, the reference voltage is correct and the last stage amplifer works flawlessly, I've also changed the filters, the first and second revisions had only an HPF to block dc and a first order LPF, the last revision has 2 HPF (first order) and a second order LPF. I didn't add a notch filtered at 50 Hz because the EOG signal has a bandwidth of about 10 Hz starting from DC, i just set the cutoff frequency of the LPF around that frequency.
The completed board 3D rendering, actually isn't very beautiful, the traces overlap with the soldermask (but way better than the 3D Canvas of the 17.2 release, that was terrifying), I'll redo a Fusion 360 rendering later
I'm ordering the PCB from JLCPCB as usual, hoping that arrives in time with this pandemic, it is such an horrible situation...