Screaming Circuits: May 2011

Day two. Custom parts

Moving on from where I left off a few days ago... I was planning on using the PIC18F2320, but in poking around, I found that the PIC18F2321 is about $3.00 less expensive in small quantities. I'm not entirely sure why. Their virtually identical. The 2320 does have two 8-bit timers instead of one in the 2321, but I haven't spotted any other differences that would matter to me in this case. The 2321 has lower sleep and idle currents but I don't think that matters in this application either.

PCB123 PIC partial sch PCB123 doesn't have the 2321 in its library. I could just use the 2320 part, but to get full use out of the pricing and availability features, I'll have to customize the part so that the BOM tool can find it at DigiKey.

I had the "place component" box up already, so I just clicked on "manage Parts" and started filling in the information in the middle column of the dialog. The I clicked the "Select Simple" button, searched on "2320" and selected the symbol for the PIC18F2320-I/SO. So far, so good.

PCB123 manage parts dialog Now, the question is: do I select "Apply Changes" or "Create a New Part"? This would be easier if I actually looked at the documentation or something, but am I doing that? Of course not. I'm going with "Create a New Part." Oops. Needed to select or generate the footprint first. Do that and search on "SOIC" and pick out an SOIC28, "Create New Part" and save it in a Library. I picked "Microchip."

Done. Now when I go back to the Insert / Add Part function, I search on PIC18F2321, and there it is. Apparently, I did it right, because the BOM tab will find it and show price and availability at DigiKey.

Duane Benson
And, today, it's not just a rain cloud, but a full one


Rain, Rain, Go Away

It's almost June her in the Pacific Northwest. At least, that's what the calendar says. I'm not sure I beleive it at the moment. The weather is acting more like October. It's a bit warmer than January, but every bit as wet. That pretty much equals October. We'll just call in Junetober.

And what does Junetober have to do with electronic assembly?

MSD logo Moisture. That's what it has to do with electronics assembly. Most of the parts running around int he world today have some level of moisture sensitivity. Despite my lament of the rain here, you have to consider component moisture no matter what your climate may be.

Looking at IPC-M-109, you can see the there are sensitivy levels MSL-1 though MSL-6. There are acutally eight levels: 2A and 5A make up the extra two. If you've got an MSL-1 part, you really don't have to worry about. I wouldn't store it in your fish bowl, but the standard says you don't have to bake it. Up at MSL-6, you have to bake the parts before use no matter what.

When you buy your moisture sensitive components, the should come in a moisture barrier antistatic bag with an indicator card and a little baggy of moisture absorbing dessicant. The best approach with these compontnts is to leave them in the original un-opened bag. We'll use what we need and properly seal up the rest just the way IPC-M-109 wants us to.

If you do need to open the bag and ship parts to us without the moisture protection, we may need to bake them for a while to make sure they are properly dried out before putting them in the reflow oven.

Duane Benson
Gore-Tex is a registered trademark of W. L. Gore & Associates.

CAD This or CAD That

I use Eagle CAD a lot. I can get away with the "Light" version, because the designs I create are small and non-commercial. I do use them sometimes to illustrate points here on my blog, but I think that still meets the qualifications of their free version. It's a good program and the multiple license levels from the free version up to the full professional version add a lot of flexibility to have the software grow with you.

Our partner, Sunstone, builds most of our PCBs here, which is a nice segue into an alternative CAD package. There are a lot of reasons to pick one CAD package over another. I won't go into that here because those reasons tend to be specific to the application. Most CAD packages are sold as a lump-sum purchase up front. A lot of them also have yearly license renewal fees. That works sometimes, but there are other times where up front costs are more important. The model that Sunstone uses for PCB123 is to provide the software at no charge and just add a little tiny bit of the software cost onto the PCB board purchase.

PCB123 isn't the only package that follows this business model and is tied into a specific PCB vendor. But, as far as I can tell, PCB123 is the only package of its sort that has enough capability to be a viable replacement for more traditional pay-first CAD packages.

I recently downloaded V4.1.11 and have started to run it through my own personal "can I use this for my stuff" test. I know it's a good package because we, here at Screaming Circuits get boards of all sorts designed with PCB123 to assemble from all manner of company. But, something can be a good package and still not fit an individuals specific requirements. Hence my personal tests.

I do find it odd, but not really an issue, that it starts you off in the layout editor instead of the schematic editor for a new design. Oh well. One click and I'm in the schematic where I can search for my parts. I use PIC chips and it's pretty rare that I find the exact chip. I always seem to have to find something close and then modify it, which just adds more opportunities for error. I know there's a jillion 28-SOIC,M28B_sml varieties, but once in a while it would be nice to just find the actual part.

Fortunately, today I'm looking for PIC18F2320 in an SOIC package. Fortunately, because it's actually there! I hit the "Insert" menu and choose "Add Part". Then I put "PIC18F23" in the search box, and there it is, but not on the computer. It was in their online labraries. (In the cloud?) It took all of about 15 seconds to automatically download the library footprint though, so first test = passed.

And the really cool thing is that once I have that part in there (for the parts found pre-made in the library), I just select the "Bill of Materials" tab down on the bottom and I can see if DigiKey has the part in stock and how much it costs.

Duane Benson
If it's in Oregon, the "cloud" is probably a rain cloud

Top-Ten Ways to Use The Summer to Your Advantage

Now, we're talking in an engineering context here. There certainly are plenty of ways to use the summer to your advantage if you like to water ski or go backpacking, but this is a specific list. Here are my top-ten suggested ways to use the summer to your advantage as an electronics designer:

Eurpoa car#Europa - Work longer. You can spend an extra few hours with you friend the Oscilloscope fighting the demons of clock jitter. With the longer days in the summer, you can do so and still get home just before sunset, as everyone else in the family is ending their relaxing evening and getting ready for bed.

#Luna - Be Green. All of those extra photons bouncing around during the summer will help to keep your solar panels producing at high-output. If only you had thirty years of continuous summer, you could pay for them before they wear out. If you live in Oregon, you'd probably need sixty years because even our summers can be pretty cloudy and rainy.

#Io - Debug thermal problems. Especially if you don't have working air conditioning. Late afternoon, the ambient in your lab will have raised up to at least 90. With the stifling lack of air movement, now is the time to turn on the high powered design that seemed to work just fine when you first prototyped it over the winter, but burps at seeming random intervals when used in the field, down in West Texas.

#Callisto - Increase your workspace. It's hot. It's clear. And, the open road beckons you. Get out your bicycle and pedal the 20 miles from home into the office. You'll be adding to #Luna, and if you don't take a shower when you arrive at the office, you'll be given plenty of extra lab workbench area.

#Mercury - Help marketing out with some product specs. Say you've developed a short-range wireless device. You know how well it works in a real world application. You've been testing it in the lab for several months now. You know how much things like walls and microwave ovens will reduce the practical range. But, it rained all winter and spring so you couldn't go outside and get the absolutely-will-never-happen-in-the-real-world range specs that will go on the brochure and be used to entice and mislead potential customers.

#Titan - Blow some stuff up. Not in the Mythbusters sense, but taking a cue from #Io, you can forget to plug in the cooling fan on your deck of MOSFETs in that new H-bridge you've been working on. Crank the PWM up to about 95% and they seem to be handling things okay - at least from the outside view. Then, with the confidence built from that exercise, put a heavy load on the motor and set the PWM at 20%. It's not gun shots. It's not popcorn. It's exploding MOSFETs!

#Ganymede - Waste some time. This works best if you have a window view. You've got a lot to do. You're overworked, underpaid and not given the help you need to get your job done on time. Rather than stressing out of all of that, arrange your cube so that no one walking by can see you monitor, but you have a clear view out the window. Then sit back in your chair, stare past your monitor, out the window and daydream about golf and barbecuing. People will think you're pondering solutions to design problems.

#Mars - Get more glory. All of your co-workers have been ahead of you throughout the winter. They've finished their projects and get to take vacation while you slave away back at the office. While they're out, fake problems in their designs and then fake the solutions. They'll all get reprimanded when they return and you'll be the star of the department. At least you will until the next design review when your boss wants to know why your design is only half finished despite how busy you've been all summer.

#Venus - Slip out an actual working product. This is the complement to #Mars for people who are actually good at their jobs. Normally, you'd be under artificially created pressure to release the project before it's quite ready. There's some press tour or show or something else that everyone wants it done before. You mess with the company vacation calendar so that the people who want to show it off are never in the office at the same time. That way you'll be able to ge that extra couple of weeks you need and should have been given to make sure the thing works right the first time and every time.

#Earth - And, drum roll please, the anti-climactic #Earth way you can use summer to your advantage: Clear your head. It's been a long, rough year, with downsizing, parts on allocation, competitive pressures and a host of other factors that have put you on the fast track to breakdown. Schedule yourself some vacation time. Leave all that junk behind and take your mountain bike to Moab or something. Just don't take a sharp left when you're on the "Killer B" trail.

Duane Benson
Don't look! Heisenberg may have been right.

Loooooooow Power

ESC Microchip clock 001 (Large) It's not quite grape power, but over in the Microchip booth, the EverReady folks were handing out little digital clock demos. Nothing sounds the least bit interesting about that, except what they're really showcasing is a little Microchip step-up DC-DC converter, the MCP1640. They're using that little chip and an Energizer 1.5V AAAA cell to power the chip at 3.3 volts. ESC Microchip clock 003 (Large)

Looking a little closer, it's a PIC16LF1933. On the other side of the battery, there's a set of six unpopulated pads labeled J1. I'm guessing that's the ICSP port. I do have MPLAB on my laptop here and I have my hand, dandy PicKit 3 with me as well. What I don't have with me is a soldering iron and a spare header... Actually, now that I think about it, I do have some six-pin headers down here with me. I might be able to put in into the PicKit and then just hold it tight to the solder pads. I'll probably sleep tonight though instead of staying up and writing something fun for this to do. I'd probably spend most of the night just trying to get the fuse bits figured out. A project for another day.

Duane Benson
It's a little big to strap on my wrist

Blackout at ESC

There's always excitement at ESC. Almost always, anyway. I think in 2009, it was mostly just spooky quiet. If I remember correctly, the theme for that year was: "but I'm not dead yet..."

Our booth, 823, is across from LeCroy this year. They do cool test equipment. I visited them a few years back to get humiliated by Guitar Hero on the Wii. I didn't play guitar hero this year, but I did get to watch the line for their beer cart and the longer line to get the little robots from Atmel, also near us.

Being mostly stuck in my booth, I haven't been able to get out and about much to see what else is here, but  Blackout fortunately, some of the excitement came to me. At approximately 4:36, the hall went dark in black out. As you can see from the photo, it was completely out except for the occasional dim glow of a laptop here and there. Me and my booth crew considered doing some looting, but we couldn't agree on who would pick up a chair and throw it through a window or a monitor.

Half a minute later, we had some emergency lighting and about ten minutes after that, the main lights started coming back on with the convention center's generators. The power stayed out for the final 45 minutes of the show. As frequently happens, stories of unknown legitimacy started flowing around. The best was that the power was our from Gilroy to just South of San Francisco. Record heat was given as a reason in one case. I'm not sure that 80 degrees should qualify as record heat, but who knows.

Back at the hotel, the elevators were running slowing on generator power. I chose to take the stairs. After a brief stop in our rooms, we were going to go out and hunt down a wild beast to cook on the open fires in the street, but the power came back on and we couldn't find any open fires.

Duane Benson
Tomorrow we we eat ham and jam and Spam a lot.

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