2013-08-13 Getting A Design Made Into A PC Board

Paul sent me an email with some questions about making a generic Joule Thief PC board  and getting it made into some PC boards.  I advised him about using the free ExpressPCB software to design the schematic and PC board, and their service to fabricate the PC board.  They charge 66 dollars U.S. for a “Miniboard” which consists of three boards, each 2.5 inches (63.5 mm) by 3.8 inches (96.5 mm).  Each board can have double layers and if you want silkscreen they charge extra.  Check their website for all the options and prices.

One of my answers was:

They want to [lock you into their service], but Futurlec say that they accept ExpressPCB files.  I’ve never used their service to find out, though.  Some PCB fabs charge a fixed setup fee and then by the square inch or cm.  if you do the numbers, you may find that the fixed setup fee makes the cost higher than ExpressPCB until you go over a certain size, which may be more than you want to buy, especially if you have small PCBs.

So you have to do some calculations to find out how much it’s going to cost per board with all the fees and stuff.  I remember Akimitsu Sadoi (the LED Artist) emailed me about a service that he uses, but I can’t remember the name.  I think it aggregates several members’ boards and submits them periodically, but the service accepts Gerber files, which require Eagle CAD (free) software or other similar s/w to generate.  And as far as I know, there is no way to convert ExpressPCB designs to Gerber, so all of my designs would have to be redone using Eagle.  And I don’t have a Windoze PC at home to do any designs, ExpressPCB OR Eagle.

Galaxy And Proselytizing

I bought a Galaxy S4 last weekend, from Google Play for $701.  I stopped at Wal-mart this evening and bought the T-Mobile SIM only package for $40 which gives me unlimited test and data, no contract, but only 100 minutes a month talk, for $30 a month with T-Mobile, which I already have.  I went to the T-Mobile store and they don’t offer this package, they want you to sign up for the full unlimited everything for $60 a month.  My existing cell phone plan has only 300 minutes, and I seldom go over 100 minutes a month, so I’m okay with this plan.  Wal-mart has other plans, too for various prices, but this particular plan is only offered in store for some reason (probably because if people could get it online, the T-Mobile stores would lose a lot of business!)

My point is that I do have a Windoze PC at work, but I’m mostly away from the office and I already use the iPod and WiFi for some stuff, but I and most everyone else is going Mobile and Windoze is becoming a minority OS, and all the software that has been Windoze only is becoming less and less accessible.  One time not long ago Microsoft Windoze had 80% of the OS, with the remaining 20% split up between Macs and Linux users.  Now the number of devices out there running Android and iOS has far surpassed the number of desktops and laptops, something in the order of billions of them worldwide.

The resolution of the Galaxy S4’s screen is 1920 by 1080, better than my (less than a year old) desktop with a touch screen.  People are carrying around their tablets (iPads, etc.) that do just about everything they need and they don’t have to be tied down to a desk.  The writing that I see on the wall from the perspective of the user support at my employer is that if the companies that have Windoze only apps don’t start converting them to run on Android and iOS, they are going to lose their user base because people are just not going to pay for having a Wintel PC at home that they have to have to run just one or two programs that remain locked into Wintel.  They will demand that if the companies want their money, then it has to run on a tablet or smart phone.

Back to the PC Board

So much for the proselytizing and back to PC boards.  Especially about my designs and the philosophy behind them.  When I designed the Blue Blinky, SJT Flasher and a few others, I made some conscious decisions about how to add some fudge factor to allow me to make mods later.

I had one basic circuit in mind when I started the design.  I had made a schematic of it, and had more than one prototype of the circuit, sometimes with some variations in them  But I also drew up some alternate circuits that I thought I could incorporate into the design by adding a few extra parts and traces.  One was to be able to add a rectifier and filter capacitor to the output to supply DC to the LED or other load.  But the board was based on the basic design that I knew could be used no matter what the results – good OR bad – were when I tried the alternate circuits.  One thing I found was that if I drew up the schematics, I could keep the board layouts separate in my head, and go back to one or other of the schematics to check and verify the layout.

I drew almost all of the traces extra wide – 50 mils – for two reasons.  One was that if I wanted to add a component later, I could drill a hole for a lead right in the middle of the trace and still have enough left to be able to solder the lead.  Also I wanted the traces to have very low resistance to minimize the losses at the very high currents and low voltages at which Joule Thiefs operate.  So if you think my circuits are ‘thick’, then now you know why.

I made custom size holes so that there was more copper around the hole.  I also made the hole slightly larger.  I wanted to have more copper to hold down the hole to the board so that I could unsolder and change components without having the copper pull off the board due to being reheated and unsoldered multiple times.

My boards were double sided, but the component side had just a very few short traces.  Since the board had no silk screen, I used the component side for text to label the boards with name, version number, and other info.

I put two large holes in the board to allow me to put a wire tie through the holes, and through the center of a toroid, to hold it to the board.  Or else put a blob of clear silicone between the toroid and the board, and let some of it ooze through the holes to hold it better.  The holes could also be used to screw the board down to a case.

In The Zone

When I designed the board, I had to concentrate intensely on the design, and exclude everything else.  I would ne be able to do it with distractions around.  The design requires a lot of decision making and visualization of what it is going to look like above the board: how are the parts going to fit together, and what leads might have to cross over others if I decide to put a component in a certain location.  This design doesn’t have autorouter software to make these decisions for me!  I have to visualize the various possibilities of putting the components and their relation to others.  I literally have  to zone in to what I’m doing as if it was some kind of game and there were many decisions that I have to make in real time.

Do I want to stand that resistor up and save board space instead of leaving it flat?  Would it be better if the electrolytic capacitor has the plus and minus swapped, so that the traces don’t have to get too close?  If I swap the + and -, is that going to confuse the person putting in the parts, since the leads are opposite of the positive and negative power buses, which are on top and bottom?  At the same time I have to keep in mind the schematic that I have decided on, and what components are going to be used.  Also, should I consider leaving more space around a certain components, because I may want to change it later?

If I make the wrong decision this time I can always redo it and resubmit the board design later, but it will cost me another 66 dollars; it would be a lot cheaper if the design was right this time.  There are so many things that I have going on in my head that I have to zone in on the design and exclude other distractions.  This is difficult and I have to be in the right mood for it, and it doesn’t happen any time I just want it to.  Therefore I can’t do designs very often and it is very taxing when I do one.

I learned that if I instead used a more professional software package with a BoM (Bill of Materials), autorouter and other features, it would automate many of the things I had to do in my head.  The BoM and library have the part number and the dimensions of the part, and other information such as the cost.  When those are known to the software, then the appropriate component layout gets chosen.  The user doesn’t have to worry about if the part is going to fit and a lot of other things.  But this software costs hundreds or thousands of dollars, so it’s out of reach of the average hobbyist.  Eagle has a limited version for free or low cost, though.  But as I said, I don’t have Windoze at home.

The result of my efforts was worth it.  I can put together one of the circuits in a short time, and it works without hassle.  It looks much better, and with my Blue Blinky, the long board with two loops from a paper clip make a convenient battery holder.  I’ve been very pleased with the PC boards and my efforts.