Screaming Circuits: Microcontrollers

On Final For Landing on Runway 0805

S part pad shift in oven process Keep out areas can be a problem when adapting a CAD component land pattern, but that's not the only potential problem. Sometimes the part may be close, but the footprint is different enough to cause problems, as in the picture on the right.

You can also run into issues that don't necessarily cause PCB assembly problems, but can be expensive none the less.

Say you are designing with a small microcontroller and the schematic symbol and land pattern don't exist for the one you're using, but something close does. Even though the two parts may look like pin for pin replacements, they may have a few differences.

The PIC family has a number of examples of this. For example, the PIC18F2321 and the PIC18F2455 have enough similarities that they look like pin for pin replacements. However, upon closer inspection, you'll find that RC3 exists on the 18F2321, but doesn't on the 18F2455. SCK/SCL and SDI/SDA are in differnt places on the two processors. You could end up with a bunch of jumpers and a PCB re-spin if you just used one land pattern for the other. It pays to check for those little details.

Duane Benson
Turn left at the big tree, and go until you see the creek.

I'm a capitalist and I'm okay...

I'm a capitalist and I'm okay
I work all night and I sleep all day

300px-LaunchPad_wireframe Well, I don't work all night so much anymore. I used to.  I am a capitalist though. I think money is good (what some people do with it, not so much). And, I also think that when people make money, they should do so in such a way that others benefit as well. That's one of the reasons I like Ti's Beagleboard so much. Speaking of Ti, they have another microcontroller product that I'm excited about as well.

The MSP430 LaunchPad is a little development board designed for education in general as well as familiarization with the MSP430 line of microcontrollers for experienced developers. (I hope they don't mind that I'm using their picture on the right here. I don't have one so I couldn't take my own picture of it.)

A lot of companies have development boards for their chips. That's nothing new. But what is really cool is that they have set a retail price for this of $4.30. Yes, the price of a 16 ounce latte.

Now I know that a latte is important. Some people have speculated that civilization would collapse without caffeine. But, here's what you get in the place of that latte: (from the Ti website, again)

"For $4.30, the LaunchPad includes a development board, 2 programmable MSP430 microcontrollers, mini-USB cable, PCB connectors for expandability, external crystal for increased clock accuracy, and free & downloadable software integrated development environments (IDEs)"

Cool. I can explode one and still have another to finish the project with. I'm going to get me one of these and spend some time with it. I don't have any personal experience with the MSPP430 line, so it will be filling it's primary mission.

On the subject, I ran across an interesting website dedicated to the MSP430: If you're already a 430er or are just intrigued by the chip, go check it out.

Duane Benson
Buttered scones, anyone?