Posts Tagged ‘XBee’

Life Update and Checkerbot Follow Up

Wow, it’s been altogether too long since I’ve posted.  Fortunately, and this is important, I’ve been able to spend a lot of great, quality time with my family.  We recently had a great time at the Oregon Beach and at the A.C. Gilbert Children’s Museum since my return from interning at the Robotics Institute at Carnegie Mellon University. (No, really, I was there!)  I’d been away from the wife and kid (“kids” including the one due in September!) for about a month, and it was great to be back.

For just a paragraph or two, I’ve gotta spill some philosophy.  Even before you have a family, and especially after you start one, hopefully everything you’re doing is for their current or future benefit.  There is nothing that can replace the fulfillment of a loving family, and like all great things, it requires preparation.  An interesting point of fact that is that Sam Walton, someone who spent his whole life innovating and who founded the largest retail chain in the world Wal-Mart, determined that he failed in life.  His last three words, given on his death bed while surrounded by his family that he hardly knew, were “I blew it!”

No one’s perfect, it’s just important to be making progress rather than regress.  New goal in life for me: Don’t blow it.  I gotta make a little bit more effort in that area, and I’m thinking even just a random act of kindness or two a day for the people I love will help.  Now, go to your room and think about it for 10 minutes, then come back and read the rest of my post. ;)

Me standing next to Boss, winner of the 2007 DARPA Urban ChallengeI had an amazing time at the Robotics Institute.  That’s me next to Boss, the autonomous Chevy Tahoe that won the DARPA Urban Challenge a few years back.  It drove itself, without collision and following all normal traffic rules, through a 60 mile urban obstacle course.  It is one of the most famous robots alive.  Boss vs Brad: Brad loses.  Boss vs Millenium Falcon: I’d love to see that show up on Youtube…

I got to work with a great group of people on a really fun, agriculture related robotic project.  I’ll probably share more on that in the future, but it’s not for me to talk about yet ;).  Most of the people around me were working on the Google XPrize project, and it was awesome to see that and other jaw-dropping amazing projects in the bay I was in.

I’d like to share a follow up post on how the checker playing robot went.  It was pretty fun, albeit stressful.  We knew at the outset that the chances of successfully navigating this project was 3,720 to 1, but we decided the risk was worth it.  Plus, we figured we could call the support desk to help us get through any ID10T errors.

The robot was based on the new XMega AVR processor.  It has quite a few more features than the standard AVR chips, which also made it a bit more difficult to use.  I recommend AVR processors highly, but unless you need functionality only provided by the XMega series, I would recommend most beginners stick with AVR chips from the ATMega series.  This project, however, needed the higher processing power, the larger RAM, and the higher flexibility of peripheral hardware offered by the XMegas.

I don’t want to repeat too much of the description of the design and process that my lab partners and I went through to do this project – it’s already available on the project website here.  You can download the SolidWorks CAD, EagleCAD, C code, and other project files from there.

So it wasn’t quite capable of playing checkers at the end of the term.  Our grades took a bit of a hit because of that, too, but it was great to try something new and the reason for this design is as follows:  We tried tackling this problem from a user’s point of view, which is something I believe is left out of academic and commercial projects all too often.  Who likes to play checkers?  Children and old men in the park.  Most other robots in the class were gantry or industrial robot arm based and relied on a laptop tether to function, which could never be practical when used by children or the elderly for safety, expense, and ease of use reasons.

Our robot weighed in under a pound and was, at least theoretically, easy to use and setup.  It used AA batteries and would be safe for anyone to use, and not expensive to replace if broken.

Now, if only it had worked :D.  The robot performs computer vision by reading images in from a UART based camera directly into the RAM of the XMega.  The XMega then determines where the checker pieces are at, calculates moves, and then goes out onto the board to execute those moves.  We fell just short of what was needed for full functionality in most areas due to lack of time and lack of experience with certain components.  As you’ll see in the video, poor motor control and localization was the primary point of failure.  Check the project website for a more detailed synopsis of what worked and what didn’t.

In this video, the robot has just captured an image and is moving from the image capture location to the checker board to make a move.  All decisions were autonomous, but the bot was stepped through its motions one step at a time and assisted when its localization or movements were out of place.

XBoot – Quick Start Guide (for a sweet XMega bootloader!)

So in my recent XMega wanderings,  I needed a good bootloader.  After muddling through various app notes and forum postings, I came across the culmination of what I couldn’t do on my own – XBoot!

In my defense, I’ve worked on bootloaders before.  But the errata sheet on the XMegas is longer than the list of men Princess Leia has broken the hearts of.  And I’ve become one of the many casualties of that list.  (Erm, the errata list…  awkward…)

Big thanks to Alex Forencich!  XBoot, a fantastic reincarnation of the AVR1605 app note, is open source and highly configurable bootloader, which at the time of writing is capable of UART or I2C bootloading XMega processors.  I believe his intentions are to expand both processor compatibility and protocol options, so visit the XBoot Google Code project for more info.

I’ll  be going through and explaining the options that I used, so this isn’t an exhaustive tutorial.  This guide assumes you have a working XMega development environment, AVRDude installed, and SVN (if you want to download the code this way).  WinAVR should work just fine with a few minor alterations, but I’ve only tested this on Kubuntu with the development environment described in this previous blog post.  Also, as a side note, I’ve been using XBoot with XBee Series 1 wireless modules and it works fantabulous (that’s so good, I had to come up with a new word for it).


Here’s the step-by-step big picture:

  1. Download the code.
  2. Pick a bootloader entry method.
  3. Configure communication parameters (Port/Baud Rate/I2C addressing, etc.).
  4. Compile & program XBoot onto the MCU.
  5. Send main application via XBoot and AVRDude.

Download the Code

So let’s get started.  Download the code from the XBoot download page and uncompress it, or (my preference) use SVN to download the code:

svn checkout avr-xboot

Configure XBoot

Once the code is downloaded, find the file named “xboot.h”.  Most configuration changes, if not all, will be made here.  We’ll take it one section at a time.  Line item references are from Rev12 out of the repository, but you should be able to match them up to any version.  The idea is that all available options are enabled, so comment out what you won’t be using.

// AVR1008 fixes
// Really only applicable to 256a3 rev A and B devices
//#define USE_AVR1008_EEPROM

Uncomment this line if you’ll be using an XMega256a3.  This fixes certain problems (remember Princess Leia the errata list?). I’ve heard this has hit some people but not others, even on the same silicon revision.  It may be useful for certain other chips and families – YMMV.  Check with Google if concerned.

Line 64:
// bootloader entrance
//#define USE_ENTER_PIN
//#define USE_ENTER_I2C

Here I picked the “USE_ENTER_DELAY” and “USE_ENTER_UART”, hence I commented the other two out.  Note that the “USE_ENTER_DELAY” just puts a delay at the start of the program, and isn’t mutually exclusive with the other options.  Here’s what the options mean:

  • USE_ENTER_DELAY: Delays entry by a timeout.  Timeout is set by “ENTER_BLINK_COUNT” and “ENTER_BLINK_WAIT”, but I found the default settings worked well.
  • USE_ENTER_PIN: Select this option if you want to enter the bootloader when a pin is in a certain state at power on.  Ex: You press a switch when you power cycle to enter the bootloader.  You’ll have to configure which port/pin at line 95, at the section titled “ENTER_PIN”.
  • USE_ENTER_UART: Select this option if you want to enter the bootloader if a character is received on the UART.  This requires using “USE_ENTER_DELAY” by necessity.  You’ll need to configure the UART options at line 111.
  • USE_ENTER_I2C: Select this option if you want to enter the bootloader if a byte is received through I2C.  I haven’t used this option, hence I won’t try to elaborate.

On to the next section:

Line 73:
// bootloader communication
#define USE_LED
#define USE_UART
//#define USE_I2C
//#define USE_ATTACH_LED

I’ll be using the UART and LED, so everything else is commented out.  If you use the LED, configure the next section also:

Line 106:
// LED
#define LED_PORT                PORTA
#define LED_PIN                 0
#define LED_INV                 1

If you’re using the UART, configure this section:

Line 111:
#define UART_BAUD_RATE                  19200
#define UART_PORT                       PORTD
#define UART_DEVICE_PORT                D1
#define UART_DEVICE                     token_paste2(USART, UART_DEVICE_PORT)
#define UART_DEVICE_RXC_ISR             token_paste3(USART, UART_DEVICE_PORT, _RXC_vect)
#define UART_DEVICE_DRE_ISR             token_paste3(USART, UART_DEVICE_PORT, _DRE_vect)
#define UART_DEVICE_TXC_ISR             token_paste3(USART, UART_DEVICE_PORT, _TXC_vect)
#define UART_TX_PIN                     PIN7_bm

Should be pretty self-explanatory.  You should only need to change UART_BAUD_RATE, UART_PORT, UART_DEVICE_PORT, and UART_TX_PIN.  If you use an exotic baud rate (non-standard and/or fast), you might want to change the settings at line 51 and select the 32MHz clock option.

That’s pretty much it for this section!

Compile & Program

This should work if you’re using AVR-GCC in Linux.  I can’t vouch for WinAVR, but it shouldn’t take much to change it.  That said, the only thing that really needs to change in the Makefile is the programmer name and the chip you’re compiling it for:

Line 42:
# MCU name
## MCU = atxmega16a4
## MCU = atxmega32a4
## MCU = atxmega64a1
## MCU = atxmega64a3
## MCU = atxmega64a4
## MCU = atxmega128a1
## MCU = atxmega128a3
## MCU = atxmega128a4
## MCU = atxmega192a1
## MCU = atxmega192a3
## MCU = atxmega256a1
## MCU = atxmega256a3b
MCU = atxmega256a3
#MCU = atxmega64a3
#MCU = atxmega128a1
#MCU = atxmega32a4

For me, I’ve been using the XMega256A3 chip.  At random, I decided to uncomment the atxmega256a3 line.  YMMV.

Line 209:

And I’m using an AVRISP mkII programmer, which is pretty cheap for an authentic Atmel programmer.  It only does PDI programming (no debugging), and needs to be updated to the latest firmware using AVR Studio (sorry, penguins – you’ll have to boot into Windows), but it does the XMega trick right nicely.

To compile and subsequently program:

$ make
$ make program

This should compile and program XBoot into the programmer.  Shazaam!  If you get any errors, feel free to leave me a comment and I’ll try to help you out.

Programming an Application Via XBoot

So now that you’ve got XBoot loaded, you can use AVRDude again to program your application to your XMega:

avrdude -p atxmega64a3 -P /dev/ttyUSB0 -c avr109 -b 19200 -U flash:w:main.hex

For those of you who may have installed Eclipse as described in previous posts, you can make Eclipse use the bootloader by:

  • Click on “Run -> Run Configurations…”
  • Right click on “C/C++ Application” on the left and select “New”
  • In the “Name:” textbox, enter “Program via XBoot”
  • In the “C/C++ Application:” textbox, enter “/usr/bin/avrdude” (or where ever it’s installed if you’re using Windows)
  • Click on the “Arguments” tab.  Enter the following line, modify to suit your needs, and then click “Apply” and “Close”
-c avr109 -p x256a3 -P /dev/ttyUSB0 -b 19200 -e -U flash:w:Debug/eclipse_project_name.hex

There you have it.  As always, if you need any help just ask in the comments below!


svn checkout avr-xboot-read-only

Checkers? What the … oh … Checkers!

In case you’ve noticed, my last few posts have not been about the ZephyrEye.  Not to fear – ZephyrEye is alive and well!  Boards should be readily available soon.  So for everyone out there interested in hacking together some Battlefront radar screens with your paintball/laser tag buddies, it is coming shortly.  Of course, if you can’t wait, feel free to grab the schematics and spin your own PCB ;)

So what the heck have I been posting about?  As I mentioned previously, I’m taking a Mechatronics course where we have to build a checker playing robot.  Here’s a conceptual animation for the design that my team and I came up with:

I used Blender3D to animate this video.  I’ve found with several of my robotics projects that most people get confused when I try to describe it.  By making a rough 3D sketch and animating the intended functionality, I’ve been able to talk with people much more effectively and get faster and better feedback about what will or won’t work.  It also helps me get several jumbled and mixed together concepts in my head down to a single, better defined concept.  If you’re planning on doing robotics, especially if you’re working on it from an electronics point of view, I’d highly recommend learning a 3D sketching system.  But I digress…

So this checker playing robot needs to be able to play checkers completely autonomously.  Most teams used either a stationary robotic arm or gantry style approach.  I’ve never been a big fan of either, in fact, I’m pretty enamored with the concept of small autonomous mobile robots.  A big reason for this is the ability to quickly apply swarm concepts to these robots if you build a few up, which is something I always toy around with in the back of my head but never do.

Here’s some of the primary system components and a simple description of each of them:

  • XMega256: Pretty powerful little chip.  I both appreciate this chip and its potential, and at the same time can’t believe how long the errata list is.  It’s pretty bad, but fortunately I haven’t run into too much trouble yet.  I’ll be using this for all of the checker-playing AI, computer vision, and localization tasks.  Yep, you heard me: computer vision on an AVR!
  • C328: OK, so the computer vision isn’t as hard as it could be – the COMedia C328 is a pretty easy to use (relatively speaking) UART camera.  The datasheet sucks, and it looks like it’s being discontinued.  I’m sure other similar parts will crop up soon, though.  I’ve been reading in raw 565 RGB images into the XMega RAM and finding color blobs with it.  I can also transmit a JPEG to a computer via XBee.
  • XBee: I use these for just about everything.  I usually write up a debug interface between the computer terminal and the robot so I can debug very quickly, and portably – it’s just as easy to debug and control from my desktop as it is my laptop, making presentations a lot easier.
  • Servos: We went with servos for motor control.  As my other posts have alluded, I’m using some hacked for continuous rotation, and instead of controlling position I’m controlling their speed with a standard servo signal.  To maintain balance (I didn’t want to go down the inverted pendulum road…), the bot also has a servo with a “propeller” mounted in front.  The propeller slides over checkers as the bot goes forward and backwards, but rotates when the bot turns to avoid strafing the board and moving checker pieces all over the place.
  • IR Sensors: There’s a bank of 6 IR emitter/detector pairs on the front of the bot.  These are used to detect where the bot is at on the checkerboard.    By monitoring the difference between when a left and IR detectors hit a checker square, you can also correct and maintain orientation so you don’t knock checkers all over the board.
  • Odometer Sensors: More IR sensors, this time the QRE1113 reflectance sensors.  These sensors monitor a band of alternating light/dark colors on the inside of the wheel, so every time the wheel moves a certain distance, the XMega gets a “tick” that’s worth a certain distance.
  • Chassis: A benefit of being in school, I have access to 3D printers that can take certain CAD files and actually “print” 3D objects in ABS plastic.  We used this for the chassis, which put all of our servo mounts, sensor mounts, and other typically difficult-to-make-precise-on-prototype features a lot more accurate.  It cost about $30 – not bad for what we get.

That’s the general idea.  Here’s a picture of where it’s at right now:

Here’s hoping that I get it done in time!  I don’t think it’ll get done in 12 parsecs, but that’s a measurement of space and not time anyway …

ZephyrEye Rev2: Board Layout in Eagle

5 March 2010 3 comments

An update on Rev2 status:  The schematic is looking pretty good, albeit there are probably still some errors that will seep up to the surface.  I’ve started on the board layout, which will also help uncover any schematic errors.  Today I’d like to go through the process I usually use to layout circuit boards in EagleCAD.

In case anyone was wondering if I was kidding about the cat and laser pointer thing, here’s a great chance to find out.  Download the schematic by itself, open it in EagleCAD, and click the “Board” button (5th from the left on the toolbar), and try laying out the board.  Make sure and give yourself some time (a day or two without sleep should do it), and dig in!

So here are the steps I use when laying out a board.  After the schematic has been reviewed several times (preferably by someone capable and also familiar with the project, not just by yourself), click the “Board” button (location described above).  What Eagle does here is it takes all of your components and puts them next to a random outline.

From here, let’s just go down the list.  Note that this is just what I do for boards like this.  It gets the job done very quick, with decent quality, but others do things different and may agree or disagree with this approach – I’d love to hear what others do in the comments!

  1. Draw a circuit board outline
  2. Group components into proper areas
  3. Manually route critical traces
  4. Autoroute remaining traces
  5. Manually fix autorouter mistakes (sometimes, the autorouter makes no sense!)
  6. Run Design Rule Checks against the board
  7. Redo steps 3 through 6 if necessary
  8. Send design to the boardhouse

1) Draw a circuit board outline.

If you don’t care what size your circuit board is, this is a very easy step.  Take the default, and shrink or expand it as you get closer to finishing step two.  Chances are, however, you should make careful considerations about your intended enclosure(s) for the circuit board.  Don’t skip this step lightly, or you’ll pay for it exponentially down the road.  Case in point: ZephyrEye Rev1, from the side as shown below.  Originally I thought I would use a different case, but it was too bulky and looked horrible.  But it didn’t exactly fit in my backup case, either:  I had to cut out the side just to get it to fit.

This is what happens when you don't think carefully about enclosures ahead of time ...The result: Ugliness.

I’ve downloaded the manufacturer’s datasheet for the enclosure, and following it’s recommendation outlined the board to maximize the PCB surface area – I’m going to need it all to get it all the features packed into this tiny little enclosure.  Either modify the existing outline, or draw using wires on the “Dimension” layer 20.  The board house will router your PCB following this outline.

Another item I always forget (and actually just remembered while writing this), is mounting holes.  Some people use vias connected to ground, while others use drill holes.  I usually prefer vias, because you can set the diameter of the copper around the via and avoid routing other traces within range of the head of the screw.  It also lets you ground your circuit board to the enclosure, which is common with metal enclosures.

2) Group components into proper areas.

For most components this is pretty straightforward.  Put all the schematic elements in the same area: an IC, supporting passives, and related supporting circuitry.  But you’ll also need to take into account any special needs of that part of the circuit:

  • Sensitivity to noise
    • The digital compass would potentially have issues if placed near the transmitter, or near any high current wires due to the magnetic field around a current-carrying wire.
  • Proximity to the edge
    • The GPS circuit needs to be near the edge because it has an antenna.  You can’t trace antenna wires very far without serious signal degradation, so it gets a special spot.
    • Most components that need to be near the edge are there because they need to match up with enclosure features – measure these things out carefully when necessary.
  • Proximity to other chips it needs to communicate with
    • If you can, put inter-communicating chips near each other.  There’s considerable flexibility on this point, depending on the protocol, the speeds they communicate at, and sensitive areas that these signals must avoid.
    • Example: If you were routing wires carrying USB 2.0 at 480MHz, it would be bad news for both other chips on the board as well as your USB signal integrity if these were long.  In fact, at this high of speed, there are very specific routing guidelines that must be followed.
  • Speeds of signals that will travel on the signal wire
    • Crystal wires should always be very short.  Once you get a signal that will be up in the megahertz range, the shorter it can be the less noise you’ll get at other locations on the board.  The trace carrying the signal can act as an antenna if it is too long.
  • Analog signals need special consideration.
    • Usually, you’ll want to avoid routing communication wires (RS232, SPI, or I2C) near analog wires.  These communication wires will put noise into your analog signals, causing headaches and very weird errors when debugging the board.
    • Antenna signals are analog of the most sensitive kind, and usually need to be a specific width if they travel very far.  You may also need to “impedance match” the trace to avoid distorting the signal.

That’s not an exhaustive list, and not detailed by any stretch of the imagination.  Google for more details on any above item you fear a board you’re laying out may have issues with.  Datasheets will have very specific layout requirements as well, many have a PCB layout guide for the chip.  Lastly, check for reference designs.  These are great to follow because you know they have been proven.

Prior to routing, all the components should be grouped into logical areas.

You’ll notice the schematic is already outlined in this way.  For example, the digital compass (HMC5843) should be placed somewhere within the outline that will be away from high-current lines (e.g., lines which may induce magnetism and noise).  I picked a corner away from everything else for this guy.  It was pretty easy to look at the schematic and see that I needed to pull in C31, C34, C40, R11, and R19.  Quickly looking at the air wires, I put them in an order that seemed like would work once the traces were routed.  Then I did more or less the same for the remaining component “groups”.

Notice the surface mount components are on top as much as possible – this makes it easier to assemble, particularly for pick & place machines and/or if you are going to bake it in a reflow oven.

3) Connect Vcc, GND, and critical traces

Vcc and ground traces go first.  Usually, I go for a ground plane on top.  Some people do Vcc planes on the bottom – I’m not a big fan of this, but I have done it.  Make sure the traces are wide enough to carry the current they need to (this calculator may come in handy) – in general, they are but it’s better to make wires that carry a lot of current be thicker anyway, no sense having a bunch of fuses around the board.  I estimated my max current delivered to this board to be less than 250 mA, but I still use .024″ traces for VBAT, and 0.16 for a few of the VCC traces.

For a few of the components, you’ll also want to trace things out before you let the autorouter have its way.  You can also quarantine areas as off-limits to the autorouter for sensitive areas.  For example, the GPS circuit is pretty sensitive, especially with regards to the RF ground plane and the antenna trace.  I routed this area up ahead of time.  To make sure  areas like this aren’t touched, you can then place polygons on the top and bottom restrict, keepout, and vRestrict (for vias) layers to manage the autorouter.

4) Autoroute remaining traces

This step has a few tricky items that can make the difference between a successful autoroute and a complete failure autoroute.  Pay close attention to the setup!  Here are the steps I used:

  • Save before you start! You will NOT be allowed to use “Undo” commands after you start the autorouter.  I usually save a separate copy before I start just to be safe.
  • Make sure your design rules are set up correctly as the autorouter follows these rules while routing traces.  Use the toolbar or click “Edit -> Design Rules…” to open the DRC dialog.  Set up the rules to follow your intended board house’s manufacturing guidelines and minimum tolerances (check their website).  Here are the ones I modified from the default:
    • Clearance Tab:
      • I set all clearances to 8 mils.
    • Distances Tab:
      • Copper/Dimension: This is the minimum distance between any copper (whether a trace, polygon, or component) and the board outline on the dimension layer 20.  I set it to 10 mils.  If you route traces too close to the edge of the board, they may get cut or damaged.
      • Drill/Hole: Distance from anything to a hole on the board.  Set to 8 mils.
    • Sizes:
      • Minimum Width:  This is the minimum width of a trace, and the autorouter will use this for everything.  10 mils is a good minimum if you have plenty of space – I used 8 mils.
      • Minimum Drill: This is the smallest drill size available from your board house.  20 mils for me.
    • The rest of the defaults generally work fine for me, but make sure you’ve met all your board house requirements before continuing.
    • Click “Apply” and then either “Check” or “Cancel”.  It’s a good idea to check your work so far to make sure you pass off a clean board to the autorouter.
  • Now click on the “Tools -> Auto…” (or use the toolbar) to open the Autorouter Setup dialog box.  Make the following changes according to your design needs:
    • Routing Grid: Here’s the deal.  The larger the grid size, the less time it takes.  But the autorouter will only consider trace joints and intersections every 50 mils.  So for surface mount components pins at, say, .5mm pitch (pin centers are .5mm apart), the autorouter will fail to connect most pins.  It will also have issues in congested routing areas.  On the other hand, using a 1 mil grid will take forever.  I used 2 mil routing grid – It took about 30 minutes.
    • Change Top and Bottom preferred routing directions if desired.  I haven’t found this to make a big difference in actual implementation, just make sure you don’t pick two parallel directions unless you want issues.
    • To be honest, I’ve never bothered playing around with rest of the settings, or the optimization settings.  I’m sure there are some advantages that can be made here, but I’ve never dove in.  Feel free to comment if you know how to change these to some advantage!

The Rev2 Main Board after being autorouted and cleaned up. Notice a few parts have moved a little to allow better routing, but not many.

Once everything is set up, save again and then hit the “OK” button.  Alternately, if you only want the autorouter to work on a particular subset of traces, use the select button and then hit the green stoplight button on the toolbar to go.  Be forewarned that the autorouter will ripup and retrace ONLY its own traces, and traces there prior to beginning the autoroute will remain untouched.  This can be a problem, especially if you have cut off certain sections of the board with traces on both the top and bottom, or have routed so close to surface mount pins the autorouter cannot place  a via to get around it.

In situations like this, and sometimes just due to trace density, sometimes the autorouter just can’t find a path for all the traces.  These will be left as airwires for you to manually route…

5) Manually fix autorouter mistakes

The Autorouter makes as much sense sometimes...

Sometimes, the autorouter just doesn’t make any sense.  I couldn’t help but post this picture – it’s a classic.

But seriously, sometimes the autorouter just does ridiculous things.  Traces have random and startling paths, take weird angles, overshoot and then overcorrect, etc.  Check through the history of the Rev2 cad files for examples.  You’ll want to shorten most of these traces if you can, take out the weird angles, and fix any traces that went through places they shouldn’t have.

And the autorouter generally uses a LOT of vias.  Vias can actually cost you extra if you use too many from some board houses, because they take extra time to drill and plate in the manufacturing process.  So minimizing vias is important.  You can usually clean a few off manually with a little effort.

It took about 30 minutes to finish the autoroute, because my routing grid was so small.  Before the first optimization step, it had around 320 vias.  Youch!  By the end, however, it was down to around 170.  Go optimizer!

It also left about 7 traces for me to finish by hand.  Most of them were because the ground plane polygon had “fallen apart”, meaning there were so many traces that parts of the ground plane had become separated and were not longer interconnected.  Many were fixed by pushing and pulling vias and traces around.  On a few, though, I had to place vias and bottom side traces that jump under traces that cut up the ground plane to make the connection.

6) Run Design Rule Checks against the board

This step is CRITICAL!  Don’t even consider sending the board off without checking your board against the design rules.  Since you’ve already got the DRC rules setup, just hit the “Design Rule Check” button on the toolbar to run it.  It’s pretty straightforward: Anywhere you have traces that are too close or overlap, parts off the boundary, or drill holes that go through traces or components, you’ll get an error that you’ll have to fix by hand.

This isn’t too bad usually, but in densely routed areas can sometimes be a little tricky.  Just use your elbows, push things out, and make some room.

7) Redo steps 3 through 6 if necessary

Well, as hard as all this has been, you may find something that needs changing.  Say you forgot a critical component, or left off a significant number of traces.  Sometimes you can add these things in after the fact, sometimes this is as practical as putting Jabba the Hutt on Jenny Craig.

If you have to, don’t resist starting over.  The command to get this to happen quickly can be typed into the command bar: “ripup ! ;”.  This will ripup everything, so if there were certain traces you wanted to keep the alternative is selecting the traces to leave alone one signal at a time by leaving off the semicolon, then hitting the green stoplight to execute the command.

If you’re happy with the board, then congratulations!  The next step is to get someone to review your board layout.  A fresh set of eyes makes all the difference.  But don’t be disappointed if, even after several reviews, it comes back with a few hardware bugs.  Have Xacto knife and patch wire ready ;)

8) Send board to boardhouse.

There are a lot of boardhouses, each with different pros and cons.  Here’s a list of other houses I’ve heard good things about:

  • Personally, I use PCBExpress because of proximity – They do small, low-feature two layer boards for pretty cheap, and they ship ground for free.  Since they are also located in Oregon, I get them in two days.  They also accept Eagle files directly – no need to generate Gerbers.
  • I’ve heard good things about Advanced Circuits.
  • BatchPCB is related to SparkFun.  This one is pretty cheap @ $2.50/sq in (plus setup fee), but takes a while to get your boards back.  Time flexibility = lower cost boards.

All of the above have Internet order options.  Just upload your file, answer a few questions (usually about layers), pay for it, and you’re done.  Usually, this is when I put together my final bill of materials and get the parts ordered so they arrive about the same time as the board.

Well, that just about covers it.  I’m sure I forgot something, so as usual feel free to remind me or ask questions in the comments.

ZephyrEye Rev2: Call for Schematic Reviewers

24 February 2010 3 comments

There are a few inevitable truths in this world.  Taxes will rise, Wookies shed all over the furniture, Luke and Leia are related, and there is no such thing as a perfect first draft schematic.

The Rev2 circuit is nearly complete.  It looks AMAZING if I do say so myself.  That’s the problem, though:  I’m inundated with excitement and therefore am unable to find things that are wrong because I don’t want to find any reason that might delay getting the circuit boards back as soon as possible.

I’m calling out for a few extra set of eyes to look over the schematic   If anyone could please go to the Google code, download the Eagle CAD files and take a look, I’d really appreciate it.  If you want to make changes, let me know so I can arrange for them to be merged back in properly.  Even if you’ve never looked at schematics before, take a look and as always, feel free to ask what’s going on in the comments.

This is also a great chance to give suggestions on functionality.  I should add, it may be your LAST chance!  Please give some comments if you think you might ever build one, if nothing else just to say you think it works for what you’d like to use it for.

If you’re not familiar with CAD schematics and circuit board layouts, it might be interesting to look at the history of the .sch and .brd files in the Google Code repository.  By looking at older revisions, you can see the steps taken along the way chronologically.  I commit changes at least at the end of almost every day I work on the project.

The current Bill of Materials can also be found at this Google Docs spreadsheet.  It includes estimated pricing – it currently comes in at just under $200.  A little bit higher than I was hoping, but about the same cost as Rev1 and Chuck Norris (adverbicized) packed with new extra features!

The schematic is hopefully organized well enough for someone not intimately familiar with this project to try and understand one section of the schematic at a time.  The capacitive touch schematic is separate, because it will be a separate board.  The way it works is you put copper pads on the board, glue it to the inside of your enclosure, and it senses you touching it on the outside of the enclosure.  Pretty nifty, and a great way to avoid milling the enclosure.

Please post comments below, or add to the Google Groups discussion page.

ZephyrEye: Rev1 vs Rev2

11 February 2010 7 comments

OK folks, I’ve received quite a few requests so here’s what’s up with the circuit boards I have available.  They are Revision 1, and have some hardware bugs (all of which can be corrected with a scalpel, soldering iron, and a fair amount of skill).  I’d like to go through the rundown once here so everyone understands what’s up.

The plan is to get started with Revision 2 soon.  There are quite a few feature improvements that would make the ZephyrEye work a lot better, and I’d like to list them.  I’m not trying to talk anyone out of a Rev1 board, I will gladly send them (without charge but unpopulated) to anyone until I run out, but I would like to avoid anyone having false expectations of what it can do.  That being said, it will probably be at least a few months before Revision 2 is ready.

If you are thinking about building a ZephyrEye, please use this post to consider your options.  Remember, it really can’t do much of anything by itself – it only tracks other ZephyrEyes, so think in pairs.  And Rev2 is very unlikely to be backwards compatible with Rev1.

Revision 1

I feel kind of like I’m hanging out my dirty laundry, these are some pretty silly mistakes:

  • LCD connector is missing two traces, which requires hand soldering wires to this connector.
  • Traces ran too close under the LCD connector, so installing the connector requires bending the pins down at an angle and soldering them without the connector having full flush contact with the board.  This bug proudly brought to you by the autorouter.
  • An extra voltage regulator needs to get patched in for the XBee, which outdid the current supply capabilities of the original regulator.

Hardware that is still untested:

  • Microphone to ADC
  • ADC channel for voltage monitoring
  • Charging indicator from LiPoly chip

State of Software:

  • Has a bootloader for easy, wireless program updates
  • Can do simple system setup
  • Can play King of the Hill, but currently limited to 2 players (I currently only have two ZephyrEyes to play with ;)
  • Still has a few bugs, graphic artifacts, etc.
  • Still needs other games programmed into it.

I only have unpopulated circuit boards (e.g., bare as the day they were born), so it’s up to you to have the tools, AVR programmer, XBees, GPS module, and pretty much every other part if you are considering putting one of these together.  Alternately, if enough people request it and are interested, I might put together some kits.  Email me or leave a comment if interested.

Revision 2

On top of the features Revision 1 already has, I would like to add the following features.  Note that some of these are crucial to be successful in playing paintball with a ZephyrEye.

  • Clear epoxy filled case that can take direct paintball impact and other abuse
  • Capacitive touch buttons, which would enable the above feature.  These would replace the tact switch buttons for the menu, zoom, and power buttons.
  • Digital compass for heading compensation.  This way the “radar” is oriented the direction you’re facing, rather than just pointing north, which is a little confusing if you aren’t a well-oriented person.
  • Helical GPS antenna, for better reception when near other objects (like your arm, body, or hopper)
  • GPS module (or chipset) with higher sensitivity and output frequency (> 1Hz)
  • Swap out the Series 1 XBee for either a 900MHz XBee or a MeshNetics ZigBit module, which have longer range and more complete, ZigBee compliant firmware.
  • If possible, an optional external ZigBee antenna for better transmissions in, say, densely forested or urban arenas.
  • Use the newer, faster XMega256.  More peripherals, and runs at a blazing 32MHz.  She’s fast enough for you, old man.

Make sure and post comments here or join the Google Code project if you’d like to have input on what Version 2 will be able to do.

Edit: I’ve also just created a Google Group for project development discussions.  If you think you’d ever be interested in using a ZephyrEye, for paintball or other, please join the group and put your thoughts up.  Revision 2 hardware development will begin in earnest soon, so now is the time to ask for features.  I’m torn between adding a can-opener or laser pointer … surely your ideas are better.

ZephyrEye: Parts List

11 February 2010 2 comments

So, the stats tools on WordPress are kind of impressive … and useful at correcting idoits like me.  I’ve talked all around it, but I noticed I haven’t released an actual bill of materials and noticed quite a few people have been searching for it.  Maybe they want to build a ZephyrEye?  I’ll try to do my best to appease the masses.  It’s been quite a while since I actually built the hardware, but here it goes…

Lucky for me, and anyone else using EagleCAD, there’s a handy User Language Program (ULP) called bom.ulp that autogenerates a BOM.  It only lists items that are actually on the schematic, however, so don’t forget things: the LCD connector denotes you should also buy an LCD display.  I’ve never made that mistake though.

Partlist exported from /home/brad/Development/zephyreye/trunk/cad/ZephyrEye Rev0.2.sch at 2/11/10 1:32 PM

Qty Value Device Parts
2 LED1206 LED1, LED2
1 .01uF C-USC0603K C5
7 .1uF C-USC0603K C3, C7, C17, C18, C21, C22, C23
2 1.5K R-US_R0603 R4, R7
1 1K R-US_R0603 R1
3 1uF CAP_POL1206 C8, C9, C12
1 2.2K R-US_R0603 R2
2 2.2uF (TANT) C-USC0603K C14, C15
1 4.7K R-US_R0603 R9
4 10uF CAP_POL1206 C1, C2, C6, C10
1 10uH INDUCTOR0603 L7
2 18pF C-USC0603K C19, C20
1 22K R-US_R0603 R55
2 100K R-US_R0603 R5, R54
1 100pF C-USC0603K C11
3 470 R-US_R0603 R6, R8, R16
1 470K R-US_R0603 R3
2 470pF C-USC0603K C13, C16
1 1000pF C-USC0603K C4
1 BC108B BC108B Q1
1 EM408 EM408 GPS
1 MAX1555 MAX1555 MAX1555
1 MEGA128-A MEGA128-A IC1
1 TPS61040 TPS61040 VR_LCD

Most of the “primary” components are from Sparkfun, with most of the passives, voltage regulators, etc. coming from Digikey.  So, on top of this list, you’ll also need:

If anybody is seriously interested in making one of these guys, let me know.  If at least 10 people are interested, I would be willing to make kits at cost (should be ~10-20% cheaper), and help those wary of the SMT soldering (for a nominal reimbursement).  Keep in mind the programming either comes from you, me, or the community and that the software has basic functionality but is not yet complete.  Also, you’ll want at least two (unless you want to use it for something other than paintball/laser tag gaming).

Note: I’ve started adding a few product links in.  As I have time, I’ll fill in the rest.  Feel free to help out in the comments if you find links to products (from SparkFun or DigiKey generally) before I do.