Actually Building Something (PCB)

First Steps

OK, here is a short primer on how the good guys build things in a serious hobbyist setting.

The development is done in 2 main stages: breadboarding and PCB construction (with pre-sensitized board).

The reason for the breadboarding phase is because the Inet is great, but you can't believe everything you read on it. What you want to do is look on the WWW for ideas and then breadboard them out. Once you get them reliable and you understand their operation, you can use the technique in your personal projects.

How you do this on a budget (as it is the Great Recession) is you get cheap Chinese breadboards on eBay for $5 a piece free shipping. Like here, on eBay.

The latest and greatest idea, the only downside is that it takes longer than a week to get your stuff in, but the price is right. You can also get broken out sensors and the like for dirt cheap (basically mounted great stuff the big guys use in smart phones and tablets). $5 per component is typical, if you know where to go.

What you do is peel the backs off them and mount them to a 2' x 2' piece of plywood you can get at Home Depot. And you are ready to rock. Next step is to find inexpensive, reliable power. A cool thing I've been playing with is tablet bricks because they are reliable, ubiquitous and a lot of them deliver a strong 1.0 Amp or 5VDC. Take your soldering iron, figure out the GND and the +5VDC and you have comfortable power on the 1 amp range. As always, PC switching power supplies are great too (just get a $5 DMM from Harbor Freight and sacrifice its leads so you have a constant digital power monitor; solder it on and wrap with electrical tape).

What you do is you mount everything on your plywood. You take your Fiscar's drill (with $2 high-speed steel Harbor Freight drill bits) and you get a nice selection of dollar-store machine screws (and nuts) that you've "tackle-box-ized". Shop the 99 Cent Store for these cheap tackle boxes and pick up about a dozen of them to keep your stuff in (resisters, relays, diodes and voltage regulators). The trick with this is: mouser; but listen, you can get ready-made kits for around $70 but they have less than $5 worth of parts in them. What you want to do is put them together yourself and when you get low on standard parts (like certain resistor values) you just restock. All it takes is time to build these part kits, you put together generic BoM (bill of materials) for your tackle box kits, so you have a nice selection of standard caps, diodes, transistors, MOSFETs, tiny relays, optoisolators, MCUs like PICs, and of course exotics like NEO6Ms, pre-programmed MCUs and MCU6050s.

Modern hacking requires attention to ESD (electrostatic discharge) because a lot of your stuff has sensitive digital logic in it. The fix is basic. Take a piece of silver solder and stick it in your ground power rail so about an inch of its hanging out. Every time you get up to walk around (where you accumulate chip-killing static) when you sit back down, just run your finger unconsciously across the solder tail. You are now grounded. Formal ESC with a wrist strap is OK too. But don't wire yourself to ground by the way, as this can lead to you doing an impression of a light-emitting resistor (an old joke but a good one); think about it electrically.

OK, you BBB (in my case my BBBW), what you want to do is mount everything to your plywood so when the wife says playtime is over, you can just put it up. Also, claiming a second "junk drawer" in your kitchen is a life-saver specifically for all your little tools and tackle boxes. What you do is you get ...

Standoffs

To make standoffs, you get a length of small-diameter ridged plastic tube and you cut pieces off yourself (getting them from Home Hardware is expensive). One of my little secrets.

To attach your BBB to the plywood, mark the holes with a fine Sharpy, load your bit in your Fiscars (at a slightly smaller diameter than the screw you will use) and just sink a hole half-way through. Then take handful of screws, a few standoffs and mount your BBB in a majestic location on your plywood. Takes like 30 seconds and its secured for weeks of tinkering.

Cut lengths of SOLID CORE insulated wire and strip the ends with a solid professional grade wire stripper (they are cheap and so worth it). Now you have all the wire you will ever need. First step with it is to wire your breadboards power rails. Connect all the blue (or GND) rails with insulated wire and what I do is run 3.3V on the left rail and 5V on the right rail (because I'm working a lot of times with both BBB and TTL), but if just working with 3.3V parts you can wire all your rails 3.3V to cut down on confusion.

You can do strain-relief by just knotting the power cord or whatever through a hole in your plywood. Keeps you from jerking sensitive wires and cables loose when moving around.

The Plan

OK, what you do is experiment on your breadboards connecting everything with wire. We all know how to do this. Get a complete working version of the circuit(s) on your breadboard set up. This will become your master reference for the next step.

DIY PCB construction

OK, throw out everything you think you've learned about DIY PCB construction and I'll tell you how to do it the right way. (Lol jk.)

OK, what you do is stick with SINGLE-SIDED pre-sensitized board that you can get from eBay or MG Chemicals. Bear with me on this one.

What you need is a florescent source, so you might want to get the little light unit with metal stands full price. You'll need a sheet of Lexan, as its called (found at Home Depot), some printable transparency sheets (and remember that laser and inkjet use different types, so get the right type for your printer; use an inexpensive version, and you tend to go through it, so get a small stack). Ferric chloride solution is HAZMAT so obtain it locally by driving down to pick it up (as it costs $14 just for the additional hazmat on shipping). Also, pick up a bottle of "developer" (it's basically bleach concentrate). While you are running around pick up a box of disposable rubber gloves and some dollar-store foam brushes.

Forget Gerber and Eagle for now. What I want you to do is download OpenOffice (its free) and use the vector drawing program on it. Set your grid to 0.1" and snap on. Build up circles and lines of the appropriate line width. Its parametric so you get your little connection circles just right. You might have to eyeball a little with stuff like DB9s, so turn off snap and get it as close as you can (remember to turn snap back on). Remember to group things intelligently, so you can duplicate things like DIP patterns and move them around like a pro.

Don't get the bubbler. Again bear with on this one. This is how the pros do it. Get 2 glass casserole dishes for this and a small Pyrex sauce pan.

What you do is you manually transfer your master reference working circuit you have breadboarded out to OpenDraw (it's virtually identical to Adobe Illustrator but it's free). If you do it this way, it's a total shortcut. Instead of wasting weeks or months on learning stuff you'll never use, you just transcribe from the physical circuit to vector drawing program. And it works like the dickens. When you are ready to go to PCB load your transparency sheet and print. Cut it out with a pair of scissors.

Wipe clean your Lexan (maybe even wash it with your dishes, so it's nice and transparent). Set up your light source and get your pre-sensitized board. OK, now STOP! I'll give you years of experience right here. The actual transferring process is very time dependent. Follow exactly (like with a stopwatch) the time recommended by the pre-sensitized board manufacturer. The reason why you use the full-price light unit and legs is because it's also distance-dependent and radiance-dependent. You don't do it right, you will have residual mask on the board that is irreparable (you just throw out the ruined board and get a new piece of pre-sensitized), under-exposed, or because transparency film isn't perfectly opaque, the light will work its way around and through the black traces, over-exposed.

I have years of commercial prototyping experience and this is the distillation of what I have discovered. It's prohibitively expensive for the hobbyist to just go through supplies like I used to to find these things out. (Elance: Rosewoodind)

OK, take the mask off the pre-sensitized board (you can make smaller boards or get a large sheet and cut it down with a regular chop saw - abrasive blade, or band/jig saw), and quickly put the transparency fragment on it (THE RIGHT SIDE UP! It's possible to transfer backward so think it through first; measure twice, cut once kind of thing). Then drop the Lexan onto it so it holds it in place. Registration isn't critically important here. But do it quickly and carefully all directly under the light source (turned off). Click your stopwatch and turn on the light source. AGAIN, exact timing according to manufacturer's instruction down to about seconds to tens of seconds.

Throw one disposable glove on your left-hand (keep you right hand normal).

When the timer expires, turn off the florescent (it's the UV from it that actually transfers, not the visible light) so you can look at the finished transfer under regular incandescent for a bit. You'll notice you can see if it transferred right as it is a slightly different color than the unexposed traces.

Pre-mix the developer (and you can do this in a lit room, it's not as sensitive as photography, just move with a purpose) directly in one of the casserole dishes. Just add water and mix well with a foam brush. Concentration isn't super-critical but measure. Temperature doesn't matter. Then drop the transferred board into the solution. Grab it with your gloved left hand and take a foam brush and wipe it periodically and gently, carrying away the dissolving exposed photomask to the rest of the solution. You know you are done when you have bright copper-clad everywhere except for your traces (this is normal) which will be a kind of green-blue color. Visually inspect.

On your stove, heat up your FC solution to very warm (this is warmer than lukewarm). Just touch your gloved left finger in periodically until you get it just a touch hotter than hot bath water. Pour it carefully into one of your casserole dishes. Contrary to public opinion FC isn't corrosive, but when warmed up (and I'll tell you how to do this) it cuts through copper like a hot knife through butter. With that said, don't get any on you as it is a real irritant. Don't touch your eyes accidentally, its like hot peppers on steroids.

Just drop your developed board into the ferric chloride solution. Heat is the key here. If it's room-temperature, you can wait all day for it to "etch". If it's very warm it only takes 10 - 15 minutes. Get a clean foam brush and manually wipe it across the surface carrying away the dissolving copper. You will know its done when the only copped left on it is under the photomask. Remember, ZERO copper left on the paper-phenolic substrate - not even flecks. They will conduct.

When you have fully etched, take the board to your sink and neutralize it with regular tap water, maybe even washing it a bit with soap. This stops the etching processes cold. You now have a perfectly etched DIY PCB. You are done for now.

Why Single-Sided PCB?

OK, a lot of you have wondered why I advocate the use of single-sided PCB. Let me justify my opinion.

When you work with DIY PCB's enough you realize kinesthetically that you can't geometrically wire up a real board with just one side (the reason why motherboards even have more than 2 "sides," they laminate several layers together giving more "sides"). Especially with multi-line buses. However, you'll find you can usually circle them around in such a way that you only need a few jumps to get finicky ones hooked up (like from one side of the board to another, or to pass a single line across a bus of lines).

What you do in your drawing program is make a connector pad circle and you put "J#" next to it in copper. Then you do the other jumper the same way with the same jumper number (so you know at assembly time exactly which pads you are jumping). Then you take a piece of insulated, end-stripped wire and you run your jumpers on the top side of the board, snaking it around the components.

The problem with double-sided and pre-sensitized is that it's pretty advanced to get the two sides to line up with the level of registration you need every time. The funny part about this is that the problem is the little whiff of air that slightly shifts your transparency mask just a fraction of a millimeter when you drop the Lexan on it during exposure. Can you do it? Yes, of course, But it's another skill to learn. To do this, just put circles with crosses through them and line them up like crosshairs.

Next Step

How do I complete my DIY PCB Board? Here are the steps: board cutting, drilling holes, mounting components, soldering, and cutting your leads.

Board cutting

You will probably want your board a certain size different than the pre-sensitized blank. You can also etch multiple boards and sub-boards on the same blank. So you can case it, etc. My opinion: chop saw with abrasive circular blade. Why? You can band saw it but you can't get it perfectly straight. A cut on a chop saw takes about 5 seconds to line it up perfectly and cut a perfectly straight cut at 90 degrees. Can I use a Dremel tool? Honey, this is America. You can do whatever you want :D

This approach is appropriate for enthusiast/serious hobbyist. Etch single-side bottom, then jumper the finicky ones on the top side. Anything else just wouldn't be civilized.

Drilling Holes

As far as I'm concerned, the way to do it is with a Fiscars drill and precision bits (Harbor Freight - $8 for a set). You just palm the drill, insert the bit and hand tighten. You will find that your copper connector pads accept the precision bit perfectly drill all the holes in the board in one operation. Tape or clamp the board to a sacrificial piece of plywood or just wood. For larger mounting holes, just use your regular bits in the Fiscars.

Mounting Components

Break out your tackle box or mouser package and lay out everything you need. You will need a scrap of paper with the resistor band colors on them. The rest of the components have their values on them. Don't cut the leads yet, it'll look like a porcupine when you are done, but just insert the part and bend the leads outward to keep them on the board - one operation.

Soldering

Use a nice hot soldering iron (just be careful). Make quick contact with point and both lead and copper-clad and touch the solder to the point where they all meet. You'll be an expert in about 2 minutes. I use a de-soldering hand pump (spring driven) for mistakes.

Lead cutting

Use a pair of "dikes". This is one of the tools you don't want to skimp on...an actual set of dikes with a spring. $2 at Harbor freight about the same size as your hand (not wire cutters - you'll find out why).