Wow!  What an exciting couple of weeks.  Sure, most folks wont care about all the fantastic things I'm about to reveal, but at least I can count on Mom to read what I write, smile, and nod. The first thing I want to share is a pencil box that I modified to hold some of my projects.  I made holes in the side for plugging in the cables.  Now, projects can sit on my desk safely without fear of being molested by the cats when I'm not looking.  The MT128 board is attached using plastic concrete anchors from the hardware instead of "real" standoffs.  The other three boards are attached with double stick tape.  You'll notice that the board in the upper right hand corner is one of my home-brew AT90USB162 boards, being used as a UART bridge. By the way, yes, I know that putting my boards in a plastic box is like running around in a thunderstorm holding up a lightning rod...especially in the winter.  I'm considering some strategies for ESD dissipation, so if you have good advice, I'm listening! ...

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This evening, as soon as Evelyn was supposed to go to bed, I snuck off to the basement.  The 2560 circuit board has a lot of holes in it, so I cheated and drilled out only the holes I would need to get the board to power up for me.  There were seven vias and ten holes for the programming header.  There were also, of course, 100 very tiny pins to solder. As soon as I finished soldering everything together, I raced upstairs to plug the board into my computer.  As these things go, instant success is rare, so I wasn't surprised when the programmer failed to detect the board.  After rooting around with a multimeter, I found the problem.  This is a problem I noticed the last time I printed the board, but somehow I failed to remedy it.  The reset pin was not connected to the programming header. A friend called this afternoon to chastise me for not simply shipping the design off to a board house to have a professional board made.  You will notice my temporary "reset" wire, connected to the programmer.  This would also be the reason I have not shipped the board out to manufacturer yet.  Once I finished the design I'll have several professional boards printed....

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When we last left our hero (yeah, that's me), he was about to try his luck with a second two layer board after his initial failure... I did.  And I failed.  Again.  The board still didn't etch cleanly the second time around, but it was better.  In fact, it was "good enough".  Using a very tiny screwdriver, I separated the many traces that did not etch properly.  That time consuming process was followed by a very careful testing process, so that I would know precisely how poorly the etching job was.  Finally, after lowering my expectations to simply being able to "talk" to the chip, I attached it to the board. This is a $17 chip, and etching a double sided, high density board is a pain in the rear.  You might imagine what I was saying to myself as I soldered the chip onto the board.  It was something to the effect of "Don't screw up.  Don't screw up.  Check your alignment.  Check your orientation." The programmer couldn't talk to the chip.  Nothing.  Nada.  I busted out the eye loupe and checked my solder...

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Over the Labor Day weekend, I could not bear to leave my computer at home.  While my wife read in the evenings, I worked out the design for my newest circuit board.  This board will incorporate an Atmega 2560, TQFP 100.  That's 100 pins at 1/2 mm spacing.  Good stuff. Now, I've done a TQFP 144 board...but it was just a breakout board.  This board actually has to do something.  That's a bit more challenging.  Getting the whole shebang to work on one layer may have been possible, but not very practical.  I have big plans for this board! (Insert maniacal laughter)  These big plans necessitated a two layer board.  My first, as it turns out. Although I have never created a two layer board, I have rehearsed the process in my mind many, many times.  The big problem is getting the registration right between the two sides.  My technique was pretty darn good.  I would glue a paper printout of the circuit to the outside of board and drill holes through the board before removing the plastic sheeting and exposing it....

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Tonight I decided to put XBee to the test.  By the time we got Evelyn in bed, it was already pretty late.  My new RC transmitter also came in today, and I had to show it my neighbor.  After we discussed our various toys and projects, it was dark out. I recently procured an ultra light laptop for my wife, and this seemed like a good inaugural use for it.  After installing the XBee tools on it, and setting up another laptop on the front porch, I wandered down the street. My first trip was short.  Only to the end of the block.  After changing the default transmit\receive channel and turning the manners down (basically, I told the transmitter to transmit even if the channel did not appear to be clear) it was time for another trip down the block. So, on I walked.  When I got to the first stopping place, my signal was still great.  Half a block later, the signal was still quite strong...but it faded rapidly.  At the end of two blocks, I had just about maximized the range of the modules.  Not bad, though.  With...

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This evening, having just gotten my hands on another USB to TTL\serial adapter, there was but one logical thing to do...revisit my XBee experiments. My initial trial with XBee was mixed.  I got the devices working, but they were incredibly unreliable from only a few inches away.  That was shockingly short of the expected one mile range. This time I decided that measuring transmission distance in inches simply wouldn't do, upped the ante.  The following photograph shows the extreme communication distance that I attempted from my secret laboratory.  Please note that the modules are separated by feet! Sadly, my results were the same.  That's unfortunate, because I had blamed poor board design on my part for the failure.  Not so.  Transmission was slow, and characters dropped for no apparent reason.  The setup would be...

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One of the things I discovered while working with the XBee boards is that I need another reliable USB-TTL serial adapter.  Since the most recent incarnation of my USB board seems "Ok", I decided to print another one and use the chip that I rescued when I wrote about the Chip Quik. When I finished the board, it looked really good.  Almost perfect.  It had nice traces with very little stippling due to over-exposure.  I drilled the board, populated it, and plugged it in. My computer complained about an "unrecognizable USB device".  Great.  I checked the traces and found one short, which I fixed.  Still nothing.  I swapped out the passive components on the board.  Still no deals.  Next, I tried a different crystal (a through hole instead of surface mount).  Finally, I pulled the chip again and replaced it with a brand new one. It still didn't work.  My pretty board was now a mess.  ...

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Ever tried desoldering an SMD?  Did it work?  I tried once.  The heatgun that I used melted many of the plastic parts on the board, but I did get the chip replaced.  It was dangerous, and I wouldn't make a habit of such operations.  After working with my USB boards, I recently decided to try using some ChipQuik to pull the chip from a failed board.



ChipQuik is wild stuff.  It comes with flux and some alloy.  You use it by melting the alloy onto the pins.  When it mixes with the solder, it lowers the melting point of the solder-making it possible to heat all the pins and remove the chip without damaging the board.  This stuff could have saved me $100 recently, when I destroyed a stepper driver board trying to replace...

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Now that I seemed to have squared away some nagging problems with my USB development board, I was ready for a new and exciting challenge: wireless communication.  In case you have never heard of XBee, you really should hop over to www.digi.com and do some reading. After not nearly enough research, I decided to purchase a pair of XBee pro modules.  These little buggers are quite small, so they don't use standard headers.  This turned out to be a blessing in disguise because they also expect 3.3v for power, and communication.  The board I wanted to use to talk to the XBee module was powered by USB at 5V.  I knew that something would have to be done about the mismatch in voltage, so I did some digging about. A company called SelmaWare created the perfect board for interfacing with an XBee, at a reasonable price.  The AppBee-Sip cost me about $12 for two bare boards, shipped.  The parts required to populate the boards cost almost nothing from DigiKey.  After getting my modules and soldering the parts to the board, I powered one up and tried to talk to it....

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