Preamp.

Since I had finished my first board a couple weeks ago, this is still pretty much all summary, although hopefully I'll be done after this. At least this enables me to skip over the rather painful details of the whole process, since I was still learning a lot at the same time.

So the physical board itself looks a bit like this:


It is, in fact, a rather simple and tame board, in retrospect. Notice the large gaping hole in the center on the bottom, along with the seven other, much smaller holes. They are just board cutouts, for placement with other boards after it was completed. The light green, the main stuff of the board, is copper, the conducting material on which charge can flow freely; the dark green is insulating material. Finally, the silvery stuff would be solder, where the copper was eroded away.

Notice the many little squares on the board? Those are pads, the parts on which the actual components would stand. Each pair would hold either a capacitor or resistor, depending on how I assigned it, and there were also transistor triplets lurking here and there. The shields around each of the 12 sections are rather unusual, however, as they are not often found on boards.

The theory behind this board is rather simple: Signals come in through the four center holes from the bottom, snake their way through the (essentially) identical circuits, each having three parts, and come out on the other end. In other words:


I really don't know what the circuits do to the input signals (although "preamp" most likely has something to do with it); I just know this is how it works. You may also be wondering how on earth do the electrons travel in such precise paths? Well, if you can make it out, there are routes within each of the shielded sections that guide them through. As for crossing each section and out into the output holes, the traces actually go a layer deeper.


This is how the board's second layer looks like. In fact, there are no fewer than four layers to the board, with every layer but the third classified as a ground layer (the third is the power layer). If you remember from physics, ground allows for the dissipation of an electric signal, whereas power would do the opposite. Hence, for this particular board, the darker green insulating material was key to producing the circuit tracing on the top: It surrounds the lighter green copper, forcing the electrons to travel along a particular path rather than dissipating through the rest of the board.

The key element allowing for the interaction among the layers is the through hole, or via. If you look carefully, you can make out (and certainly in the above CAM file) small holes scattered everywhere. They are friendly to the excited electrons, and allow them to progress from the top layer to another. Where they are supposed to flow, conducting material is soldered around the via; otherwise, they are blocked by the dark green material. A closer inspection of the back will show what I mean.


Some of the vias are surrounded fully by the insulation, others only partially. And still others have the full silvery material around them for full conduction. And finally, one of the circuits is shown below in schematic form (the other three are nearly identical), if you should want an idea of how the input signal gets to the output. Notice the many grounds throughout the circuit, as well as the one power source at the top. Some of the vias allows for a physical connection to the power layer; others link the grounded pads outside the shields for dissipation. Since layers 1, 2, and 4 are all ground layers, it doesn't make a difference where they are linked to.

Anyway, that's enough talking about how the first board works. Details of how I accomplished my goal of reproducing it in PADS will accompany those of the board I am working on now--since it is the same process, there is no point in explaining it more than once. All together, it took over a month (although that was mostly due to the learning process and my own laziness, more on that later). But it is more or less finished by now, a proud product of a month's hard work.


It is, I must admit, quite beautiful, and as close to the original as I could make it. As for the changes, they were just additions here or deletions there, but they did not impact the board very much. The one thing that did change significantly were the input and output connections at the center and bottom sides. They are no longer one huge hole (or pin, in technical terms), but five, with the major connection in the center. That was a source of constant agony for me, and they have to do with the other two boards that this particular one is connected to. But they are done with and finalized, and they will (hopefully) torture me no more.

Round One... FIGHT!

Well, not really. The first day (June 1) was nothing too intense. Mostly just getting acquainted to the place and surroundings and where my room would be, as well as meeting the people I would have to work with most. More details to come interspliced randomly later on.

Anyway, the week was relatively uneventful; I was essentially getting paid to do nothing but go through the tutorials of this new program. For anyone who is curious, PADS is a product of the Mentor Graphics company, which specializes in EDA, electronic design automation. PADS itself is actually three separate programs: Layout, Router, and Logic.

For those who care, Layout would be the one that I use most, to "lay out" the circuit boards.


Fun stuff. Actually, that was just one of the tutorial boards, not the one I was working on. It's actually relatively less complex than the one I'm working on now. The other programs, Logic and Router, aren't really used so much, even by the other engineers. Router is mainly for routing (duh?)--in other words, the circuit traces that you see up on the image above. It is a pain to do manually, which is why PADS has a program to do it automatically for you. Like any automation program, however, results don't always come out as intended aesthetically, and most people still stick with doing it themselves (including me).

As for Logic, it is the schematic editor of PADS. For any circuit board, there goes along with it a series of schematic diagrams, where the circuit is written out in a legible form. I was inclined to use this over the other program, OrCAD Capture by Cadence, since either way the schematic would eventually have to be linked over to Layout.

Unfortunately, the older engineers at the lab have been used to working with OrCAD first, then exporting over to PADS, which is a much newer program. So the schematics I received from Jim were all in OrCAD format; it's not mutually incompatible with Logic, but it was too much hassle to convert over. PADS Logic is definitely cleaner though, and I wouldn't be surprised if the engineers make a transition in the near future.

In any case, here's what OrCAD looks like.


Again, PADS Logic is pretty similar, just cleaner imo. So there you have it, the main programs with which I'm working this summer. That first week was actually pretty tough; not only was I learning how to use the programs, but I also had to learn the various terminologies and whatnot.

So after a week, with the simplest understanding of how everything worked, I was to start on my first assignment, a board that looks like this.


Oh yeah, that program happens to be CAMvu, forgot to introduce it earlier. Anyway, it's more or less something of an image viewer, allowing examination but not editing of the board. It's kinda annoying in that it's rather inflexible (maybe I just don't know how to use it well enough), but I need this as a reference as to how the original board looks like. I have the physical board too, but obviously I can't look into the inner layers of it, as CAMvu allows me to do.

In summary, I had three weapons to fight this war. The schematics for each board, which I require, provide the backbone of each board, telling how each component would be connected to each other. I have the actual boards themselves, which is useful as a real-world visual (for the outer layers anyway). And I have the CAM files, which are necessary, as Jim wanted me to do as close of a reimplementation as possible.

Details of this first battle to come.

Prologue

Sometime in mid-May (a couple weeks after I got confirmed), I went back to the lab to get logistic stuff settled and to meet with my supervisor Jim again. First I signed a series of contracts with one of the secretaries there. Literally, just "sign here," "sign there"--I really didn't read anything. -_-

Oh well, I'm pretty sure it was mostly for pay and stuff anyway. I did notice one of them stated that anything I produced would be the property of UC Berkeley. Not that I'm really "producing" anything this summer anyway.

Then Jim showed me what I would be doing this summer. He has three circuit boards (pictures to come), all of which were laid out by an engineer who recently passed away, and he wanted me to reimplement them (with some changes) on this program called PADS. Honestly, I had no idea why he accepted me to work with him; in our interview, I blatantly told him, somewhat shamefully, that I had no experience whatsoever in boards--I still haven't taken my undergrad circuits course yet.

Detour--this was the reason why I chose this job in the first place over another one. The other involved heavy programming in C, a language with which I have little experience aside from the related C++. But after some heavy debating, I decided that, for all my CS experience, I have virtually no EE to match it up--some EECS major I am. Naturally, since Jim was willing to take me, I was quite keen to accept.

Anyway, so he showed me the boards, as well as the matching schematics (circuit diagrams), and he kinda led me through them and how they worked. At the time I got lost pretty quickly; both the terminology and the complex circuitry was more than I could bear, having been exposed to almost none of it before. Yes, I took physics, but all that amounted to here was being able to identify which part was a capacitor and which part was a resistor.

Feeling fairly unconfident at the end of the meeting, I walked out of there with pretty low expectations about the upcoming summer. The learning curve seemed so steep, and how was I supposed to do a job which involves dealing with things that I have never worked with before?

SPLURGE!

Ok I'm going to be writing many posts in succession to make up for the first half. So a lot of people wonder how I came upon this in the first place.

Around mid-spring semester, my physics professor gave out an announcement in class telling us about working at the Space Sciences Lab over the summer, basically a good opportunity to gain some research experience and get some pay. Well, it was pretty simple, just submit a resume and he'll do the rest. So I did, and a couple weeks later, I was one of the several who were selected for interviews. At the time I was still expecting the SFMTA job and didn't think much of it though.

The interview took place on a Friday soon after. It was my first time going up to the lab, which was way up in the hills of the campus--it takes about 10 minutes by shuttle from the main campus (nice view though, go sometime if you can). I remember that it was also a warm day, and I was only wearing a t-shirt and shorts (thanks to the other people for making me feel bad by dressing so nicely). Well, once we got there, we met our physics professor and he handed us a huge list of names.

I looked at the list and I was like O_O--"see as many of them as you can." So basically, long story short, I went up and down and around the entire building, getting interviewed by no less than seven graduate students and post-docs and whatever else. Some were pretty chill and friendly; others were more serious and intimidating. Toward the end (3 hours later) I was becoming weary and very frustrated with one of them--I waited over 40 minutes for him, and he was still with the same guy.

Needless to say, I was pretty worn out when I got back to my dorm. Over the next couple days, I sent out emails thanking each one for the interviews. Some got back to me; others didn't. I was accepted for a couple offers, and, after a lot of juggling back and forth (and a silent rejection from the MTA), I finally decided to choose one.

Introduction

So I was showering not too long ago when it occurred to me that what I'm doing this summer will probably turn out to be pretty useful later in life. And I was talking with The Hare earlier about how people always rant to me about stuff like sports or politics, stuff on which I'm not necessarily "expertise"; why don't I do the same thing about material that I'm involved in (i.e., this blog)? I don't always understand what people talk to me about--same principle if I'm talking to others about PCB's or SMD's.

Hence, this blog (with an intended lifetime of the remainder of this summer, but who knows) will primarily be for my reflections and feelings on what I've been doing and what I will do for the next month and a half. Granted, it's pretty weird that I'm starting this like halfway in, but better late than never, I guess.