Screaming Circuits: October 2008

ZigBee, Part Two

I like the ZigBee module from Microchip that I wrote about below. But theory and practice aren't always the same, so I've ordered two of the modules to try out.

In my spare time, I sometimes build little robots and I've wanted to try out wireless for some time now. I don't have enough time to dig into the low level stuff and figure out how to do it from scratch so these modules seem like they might just be the ticket.

I'm going to see if I can integrate some ZigBee into my robots with these modules and I'll keep you posted on the progress. The modules are backordered at Microchip until November 14th, but that will give me some time to dig out some of the old bot boards and get ready. I'll prototype up the software with my old boards and at the same time, I'll get PCB123, from Sunstone Circuits, out and do a re-design to use more surface mount and shrink the boards.

Check back here periodically to see my progress and if all goes well, I'll have the actual bots in our booth at Embedded Systems Conference, Silicon Valley in April 2009.

Duane Benson
Wireless minds want to know

Easy ZigBee

I did run over to the Microchip booth. I've always been a PIC guy myself for my own little projects. Wireless has always been a lot tougher than any other form of communication (insert "duh" here) but this thing from Microchip may help quite a bit.

They've packaged up a ZigBee radio antenna (MRF24J40MA) and everything onto a little transceiver module. It easily talks to most of their PIC processors via a four wire SPI interface. I think even I could use that. And, I could buy it from DigiKey for $9.95. Very nice.

ESC 1008 Microchip (Small)

The demo shown here is a little tic-tac-toe game run wirelessly between two micro controllers.

Duane Benson
Blogging at the show is good because I get to sit down and rest my feet

Giant Blue People at the ESC Show

I haven't had a lot of time to walk the show floor yet so I don't know what's really new and exciting, or if there is, in fact, anything new and exciting. But, I did see a giant dancing blue person at one of the booths. The picture came out a little blurry from the dancing, or maybe I was just blurry from red-eye flights and lack of sleep.

ESC 1008 (Small) 

I'm going to have to run over to the other guy's booth and see if they have a giant dancing person of their own or something and give them equal time.

Duane Benson
Dance atmelina, dance

Trade Show secrets

I've been to a lot of trade shows. Mostly as an exhibitor, but do remember the days when I went as an attendee only. That was almost a lifetime ago. I was at the West Coast Computer Faire when the original Mac was introduced in 1984. I used to go to that show a lot. I saw Robin Williams there once too. Was anybody else there back then? Fun times.

Somewhere in the late 80's though, I started going as an exhibitor almost exclusively. It's pretty amazing to see the mess of the day prior and watch it change from piles and aisles of junk into a clean and professional looking event.

ESC1008-2 asle ways (small)

This is what it looks like today. This is the secret world of tradeshows that most people don't get to see. Tomorrow, it won't even be the same place. It will be full of people and devoid of trash and boxes.

Duane Benson
Fly and be free!

ESC - Waiting as usual

It's setup day for ESC Boston and that means waiting. Some of our boxes are here, but the booth it's self isn't. It always seems to end up this way. If a box or crate is missing, it's the booth. If they'd do it the other way around and have the booth show up on time and the boxes of junk show up late, we could set up and not worry about anything else.

ESC1008-1 empty.jpb

As it is, here we are, after a red-eye from Portland, waiting again. That's Matt sitting in the booth trying to stay awake. I sort of got about two hours of sleep myself. They played the movie "Get Smart" on the flight from Portland to Newark. I didn't watch it. I love the movie, but I wanted to sleep. It kept me up a bit anyway though because every so often, someone near me would break out laughing and wake me up.

Duane Benson
Bulletins as events warrant

LGA Modules and Footprints

We see a lot of newer power components - DC to DC converters, boost and buck type things in modules these days. They're getting more and more common with the POL (point of load) practice trends these days. Modules are of course, pretty common in thru-hole configuration and have become more and more common in BGA configuration. We see a lot of them.

LGA module Something fairly new though is an LGA module. They aren't too much trouble to deal with. In practice, it's not too different than a QFN. The thermal properties are of course unique to the module and we don't tend to see big center pads, but it's still very important to carefully consider the footprint.

In the case of this part, it would have been a lot better to make a custom parts library and match the pads exactly. There are a couple of opportunities for shorts and I'm not sure what the deal is with the two tiny pads on the bottom side of the picture.

Duane Benson
Hi ho. Hi ho. It's off to the show I go - the ESC show, that is

Pilgrimage to the Embedded Systems Conference

Esc_boston_08 We're going to the Embedded Systems Conference in Boston and we'll be in Booth #517Esc0407_2 on October 28th-29th. Come see us. It'll be fun. You can enter our fun contest and maybe win a cool LED Screaming Circuits flashlight and be entered to win a $2,000 coupon towards your next order!

If you stop by, we'll give you a show discount code for use on your next order too.

And here is a free ESC exhibits guest pass!

Silk on Pad

We've written about things on or in pads before. Mostly vias in pads. But this is something less common: silk screen on pads. It does happen. In fact, I wrote about it just the other day. This one though is a really extreme case.

Silk_on_pad You can see that we did attempt to scrape the sik screen off of one of the pads. Some times we can do that and get away with a decent prototype assembly, but sometimes that just adds in too many other problems. In this specific case, there were just too many cases of silk screen ink covering pads. It was all over the place and it was just too much. We can't use these boards.

There are a few things you can do to prevent this.

  1. First, dig into the parts library. Examine the silk layer and make sure it doesn't stomp on the solder area like this. Modify the library parts if you have to.
  2. Make sure your board fab house has good registration. Sometimes this is caused by poor quality control and the fab house and not the libraries, as was the case here.
  3. Select a board fab house that will clip the silk screen off of the pad area during fab. It's always better to fix the problem where it is caused, like in the library, but it's good to have a back up plan. Sunstone does offer the service of clipping the silk screen off the pads. You have to ask for it, but it could have saved these boards.

My advice to you: Always double check all of the layers and ask your board fab house to clip the silk screen just in case.

Duane Benson
It may look like a silver Oreo, but it doesn't taste as good

QFN / QFP switcheroo

Here's an all too familiar face. We see this a lot with chips that have both a QFP (quad flat pack)and a QFN (quad flat pack, no leads) package. Especially if the QFP packaged part has been around for a long time and the QFN version is fairly new.

Qfp_qfn_4 In the CAD package, the two components look pretty close. You have a center flag pad and lots of leads. Unless you have the component sitting right there with you, it's not always easy to tell at a glance that you have selected the wrong package. A quick give-away though is the length of the leads. If you have long lands for the leads like this footprint, it's a good bet that you have a QFP library part. I won't guarantee it, but it's likely enough that you should conduct some further investigation to make sure you won't end up with sad boards like these.

The reverse is true too. If your actual component is a QFP and the land pattern has very short leads, you should look closer.

Duane Benson
Quirky perhaps Mr Longfellow

Financial Fear and Uncertanty

I'm really old. I remember Black Monday back in 1987 when we all thought the business world was coming to an end. I was working for a company called Metheus at the time, making high resolution graphics systems. I remember when Microsoft lost half it's stock value in 2000 precipitating the dot-com crash. I was just a kid during the energy crisis back in the early seventies, but we all thought that was the end of the American economy. I remember that double-digit inflation back in the 70's and the double digit interest rates in the 80's.

It comes and it goes, you know. I've kind of lost track of the number of business "doom cycles" I've been through and the number of times "experts" have predicted the end of U.S. prosperity. Personally, I'm seeing this as a time to start putting more money into my 401K.

I do know though that when credit gets tough to get, a lot of companies tighten their belts. A lot of small companies retrench and bigger companies cut back. Unfortunately, for us mere working mortals, our work load never seems to lighten up. In fact, it frequently gets worse.

We here at Screaming Circuits are lucky in that we've been growing and expanding. This month we're adding a new surface mount line. We are very strong and we'll be here through this financial tumble to help if you need it. We hear rumors of pcb fab houses struggling and other ems shops struggling. I hate to hear that about any company or any industry, but I would like to reassure you that we're set to keep running at full speed. We're continuing to expand our capacity and improve our quality and service. We are here for you.

Duane Benson
When the going gets tough, the tough eat ice cream

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