Royce's Log

2D Laser Range Finder

2010-03-01T00:21:00.003-06:00

Ever since I read Ken Maxon's article: 'A Real-time Laser Range Finding Vision System', I've wanted to experiment with a similar system. This past Sunday afternoon, I finally got around to it. I don't have any CLPD chops, so I used a regular computer. Above you can see my initial rough results. The line laser registers lower in the image field for the block than for the background. The software properly converted that lower registration to a distance of about 26.5 inches.

The idea behind the concept is fairly straight forward. By angling and elevating the camera relative to the laser we can establish a trigonometric relationship between the vertical location of the laser and the distance to the object that the laser is striking. Since the laser is a line on the screen, each pixel column in the image field becomes it's own independent laser range finder.

In the picture above four possible angles are shown to demonstrate that each angle corresponds to a different obstruction distance.

Each possible height in the image field corresponds to a specific angle of light into the camera's roughly conical field of view. The line from the laser's point of impact to the camera, the vertical line from the camera to the laser generator and the horizontal laser line itself form a right triangle that allows us to compute distance. By dividing the angular field of vision by the number of rows in the the camera we come up with a formula to compute the angle of entry for the reflected laser light for each of the rows in the camera. We also know the distance from the camera to the laser generator. (Its fixed). Plugging the angle and the vertical distance in the trigonometry equation: tangent of theta equals the opposite leg length divided by the adjacent leg length, and re-arranging, we compute the opposite leg length and determine how far away the object is.

You can see my software doing just that in the first picture. The software doesn't compensate for the fact that the horizontal pixels are each their own angle as well, but in this first rough pass I felt it wasn't necessary. You'll note the the software makes no attempt to measure the left/right distances.

With a sub 5mW power level and a popular frequency (red), something like is probably restricted to a small indoor bot with somewhat short range needs. Still in complement to other scanning systems like a spinning ultra sonic range finder, I can see this adding mechanism to the reliability of local environment mapping system. If I ever build my home security patrol bot, I'll definitely think about this technique.

Below you can see the rig I used to test this idea out. It's pretty basic but it got the job done. To the left you see the paper back drop and the paper obstruction. To the right you can see the line laser generator sitting at the bottom of the dremel drill press with the webcam perched on top.

Hexamon

2009-08-08T23:45:00.000-05:00

So today I discovered two things: I have a transistor in backwards on Uno-version-Dos' drive board and I am out of de-soldering braid. :(

Nevertheless, as the wife was tied up all afternoon today, I was determined to work on robots. I stopped by Trossen Robotics and caught some of the footage of the Mech Warfare event they held at the 2009 RoboGames. Boy, it was really neat. I also caught a note from Alex that indicated they were creating a hexapod league.

It occurred to me that hexapod gaits were simple enough that it might well be a good project for me to get some custom Dynamixel gait code up and running. From there I could branch off and do more complex tasks. Custom gait code is something "I've Been Meaning to Do."(TM).

So, I spent all afternoon assembling the frame below from my Bioloid kits.

Its always shocking to me just how long it takes to do mechanical things. Looking at that pic, I think it should have taken no more than a hour, but it was actually more like four or five hours. Nevertheless, it was a fun afternoon and my head filled with delusions of grandeur as I built it.

I rather like my name too. Its from Eon. I figure I'll wind up letting this bot will ride on a whole line of design flaws, so it seems appropriate.

Uno Sensor Board Update

2009-07-29T00:57:00.002-05:00

I worked on my sensor board again tonight. I got the sensor portion, as opposed to the led driver portion, working. I had to do a bit more board repair. Apparently, when I swapped the incorrectly routed op-amp outputs and power lines, I damaged a via and disconnected the forward looking opamp from the MCU. I wound up drilling out a couple vias to fix it.

Once I had it going I tried to run a simple test program to show which of the four sensors saw the greatest amount of light. For the test I just used a loose IR LED wired to be always on at about 20 mA. I have moved the code around a bit since last time I talked about it. I don't use the timer interrupts at all now. I just use the ADC conversion complete interrupt. I discovered you can configure the ADC to automatically begin a conversion based off of a number of other interrupts. So I set the ADC to trigger off of Compare Match A for Timer 1. That interrupt is the one that raises the strobe line to the LEDs to begin emitting light for 10us. However, I don't actually have to service the Compare Match A interrupt, the ADC will begin conversion regardless. Instead I can just service the conversion complete interrupt and do everything there. The timing of the conversion is such that the sample and hold should happen somewhere around 7 us into the pulse. I've yet to verify that's really what's happening on the scope however.

Anyway my test program behaved quite oddly and only the forward channel seemed to ever detect anything. After some digging I discovered that there are restrictions on changing the ADC channel while in auto-trigger mode. Two of the three times they list that its OK to change, I could not puzzle out how to get at in code. I wound up actually disabling the auto-trigger bit, a listed time to change the channel, and then reset the bit right after the channel change. That seemed to work. But, it took about more than an hour to figure out what was going on.

I'll chalk it up to a learning experience. I've explored a corner of the AVR that'd I'd never visited before and found an annoying quirk. I'll know better next time and maybe I can get someone past the quirk in the future without them having to puzzle for an hour or more.

Rapid PCB Etching with a Sponge

2009-07-13T19:31:00.002-05:00

hack-a-day picked this up from instructables who picked it up from Pulsar. Its a story about etching VERY rapidly, in about 60 seconds, by using a tiny amount of Ferric Chloride and a sponge. I am pretty excited for this technique and will try it very shortly. I found a second error on my LED emitter board so its over-due for a re-etch. Once I've tried it I'll report back here. If you've already tried it, leave a comment and let me know if the technique lives up to it amazing promises.

Update: Unfortunately I must report failure. Tonight at RBNO I tried this technique and found only moderate reduction in etch time for a whole lot more work than an agitated bath. I think that the copper clad the fellow in the instructable is using must be quite thin indeed. I would expect that an agitated bath would run pretty quick as well. For my standard 1oz copper clad it took me 8 or nine minutes of wiping to clear the board. An agitated bath take 10 to 15 minutes, but I don't have to do anything, I just wait for the board to finish.

So, I don't think I'll be using this technique. Its a shame, I was really salivating over a 60 second etch time.

Uno V Dos Sensor Board Progress

2009-06-10T01:48:00.001-05:00

So tonight I finally got back around to working on Uno V. Dos. The part I really wanted to get working was the multiplexer driver. The idea behind the multiplexer circuit is that the 10us pulse that happens 300 times per a second will redirected to a new IR LED bank after each pulse causing the LED banks to fire one at a time in a ring sequence. To effect that, I set my timer up to generate a 10us pulse 300 times a second on the Timer1 Output Compare A pin (OC1A). That was pretty easy and I was able to see the pulse in TomG's old but still quite capable o-scope.

The pulse goes to the enable pin of the high power 3-to-8 multiplexer chip. Each of the eight outputs goes to a different bank of LEDs. So when that pulse comes in one bank and one bank only will light up for 10 us. Exactly which bank lights up is controlled by the 3 address lines of the multiplexer. I needed to swap out those address lines shortly after the strobe pulse ended when the multiplexer would be disabled, the LEDs off and there would be a goodly wait until the next pulse.

Initially I set my Timer to Fast PWM mode with the TOP controlled by ICR1 and set to about 27,000. The compare register was set to 67. OC1A was configured to set on overflow and clear on compare match. This looked great on the scope and I didn't think I'd need touch those values again. Since OC1A was set to clear on a compare match I figured that of the several timer interrupts, the Compare A Interrupt was the right time adjust my address lines that headed to the multiplexer. Wrong.

For some reason that I still not certain of, the Compare A Interrupt does not seem to fire. I know I had the Timer 1 Interrupt mask set properly to enable both Compare A and Overflow and I had the Global Interrupts Enabled flag set, but still no joy. Overflow Interrupt, however, worked just fine. Odd. Of course, the way the timer was configured, overflow was a terrible time to mess with the address Lines. It could result in two banks lighting up, each for some percentage of the 10 us time.

Maybe its just a quirk of Fast PWM mode, but by the time I determined that Overflow worked and Compare A didn't it was late and I didn't want to change the mode. I wound up setting the Compare Register to 27000 minus 67 and changing OC1A to clear on overflow and set on compare match. This gave me the same over all signal, it just occurred at the other end of the time period. (26933 through 27000 rather than 0 through 67) It also made overflow the correct time to change the address lines.

Above you can see a picture of my success. The top two pairs of lines are two of the three address lines. The last square wave at the bottom is the strobe pulse signal from the Output Compare pin (OC1A). The Address lines appear double because the o-scope is set to trigger on OC1A and the value of the address lines changes with each pulse. The rapid variation makes the high and the low states blur together and appear to be occurring simultaneously on the o-scope. However the code that actually changes the line first sets them all to zero so that a simple bitwise OR operation can be used to write the new line states all at once. This causes a noticeable glitch in the address line wave shape where all the lines are zero for a time. However, as you can see in the photo the glitch occurs a few microseconds after the LED strobe pulse comes down meaning the LEDs are off. So the glitch does not affect them. What the glitch does do is provide me a nice point of reference that allows me to overcome the blurring of states and confirm that the address lines are changing at the right time. It was a happy glitch to end the evening with!

Slow Progress

2009-04-23T00:23:00.001-05:00

Not a lot of progress this week. All I managed to do was attach my repair wires to fix the reversed power and output on the TI OPA380A chips. I haven't even had a chance to test it. With any luck I did not smoke the chips.

It took me around two or three hours of futzing to put the wires on. Just a bit faster than I could remake the whole board. Of course, if I smoked the chips, I'll be remaking it any way.

On another note I happened to run across a really neat piece of electronics art. I really dig the air-wire scheme it has going on. I can see using the technique in a trophy design.

Blunderifc

2009-04-15T17:14:00.001-05:00

Well it seems I made another blunder quite some time ago and have only now just seen it. I finally got around to firing up Uno's sensor board for testing. The Transimpedance Amplifiers immediately got hot. After poking around a bit I discovered that the library component that I created for DipTrace has the pins in descending order.. on both side of the SOIC chip. Doh. I got lucky, two of the four pins are N/C on the bad side, but the output and the Vcc got swapped.

You can see where I've begun cutting the traces on one of the four amplifiers. I hate to make this board even more ugly than it is, but if I didn't fry the chips its still a good bit less time to cut traces and solder jumpers than to remake the whole board, even with my new solder paster skills.

Side Project: Necklace

2009-04-01T13:57:00.001-05:00

My wife had been after me for a while to make her a necklace with a copper pattern. At last I got around to it this past week. I learned a few new things and it was also pretty good solder paste practice.

The necklace itself is four jewel style LEDs that run off an ATtiny13 and are powered by a CR2032 coin cell battery. The program starts the Timer in Normal Mode with a 1024 clock divisor and then goes to sleep. When it wakes up on the timer overflow it increments a variable and goes back to sleep. Once the variable exceeds a threshold the MCU makes the LEDs blink around a bit, resets the variable and goes to sleep once more. The ATtiny13 is clocked at 600kHz and the variable threshold is calibrated to make the LEDs run about once an hour.

It had been my intent to clock the MCU at 128kHz to save the extra power. The first time I tried to set up that clock I had AVR Studio set to the the wrong MCU type. I bricked the MCU. Doh! As I discovered however, with an extra person applying leverage with an exacto knife, you can use an embossing gun to pop the chip off with little to no damage to the PCB.

Having mounted a new chip I tried to set up the clock once more. After the clock was set to 128kHz I could not talk to the chip any more. It seems that little note about making sure the ISP clock is less than 1/4 the MCU clock is for real. My ISP's clock speed is adjustable, but I learned at that moment that 56k was as low as it would go. Another MCU bricked. Doh!

The third chip was the charm because I decided that I could live with 600kHz. The docs say that in sleep mode at 1MHz the chip draws 24uA. I was able to turn off a couple extra peripherals and am running lower than 1Mhz so hopefully I'm doing better than 24uA and will get a decent life out of my coin cell. However, even with the 1024 divisor the chip has to wake up more often than twice a second to increment the variable. I guess we'll see what the ultimate battery life really is.

Blunder!

2009-03-07T16:45:00.004-06:00

I've made an awful blunder in the design of my drive board for Uno. I really wanted to use these nice dual LED holders that I salvaged from a circuit board that TomG gave me. However, I was so excited to get to the part where I used the solder paste that I neglected to do any final fit measurements with the parts on paper or even on the un-soldered board.

The IR leds did not nest as deeply as the original leds and thus stick further out than I was expecting. The result is that my board is 7mm too wide per the Mini-Sumo rules. Now I am looking at desoldering as many components as I can so that I can remount them on a redesigned board. If I break too much stuff during the process I'll have to place another order. Before I start desoldering, however, I think I will power the board up and see if I can get it to work.

Solder Paste is Cool

2009-03-05T23:52:00.001-06:00

So I gave solder paste shot. I really like it. I bought a syringe of no-clean from Howard Electronics Instruments. The syringe comes with a fairly wide tip but the syringe and tip are luer lock type so you can buy all sorts of different width tips for the syringe. I wasn't 100% certain that the syringe would be a luer lock type when I bought it so I skipped buying extra tips. I found that even though the supplied tip is imprecise when the paste reflows even significant errors seem to shrink right up to the pad dimensions. What's better is that if the geometry of your pads is not disturbed by large intersecting traces the part will sqaure up automatically with the pads. (As you'll see below one cap with one pad pretty much engulfed by a wide high-current trace is a bit skewed.. but still not too bad.) Nevertheless I'll probably buy a couple/three boxes of tips.

So below is my board with un-reflowed paste on it.

(Ok I forgot a couple components )

Now here is the after photo

I used the techniue described on Cash Olsen's site (which seems to be down now). I set a skillet to around 100 degrees C, put the circuit on it and let it heat for a few moments. I let the paste flatten out a bit under the effect of the skillet heat. Then I hit each component with a $20 emobossing heat gun at a ~3-4 inch range until the paste reflowed and actually turned silver. This generally took just a few seconds for the small components.

As you can see in the after photo I left the heat gun on the 7805 a little too long and singed the edge of the circuit board. I probabyl got the gun too close. I should have been more patient from a farther distance.

I still need a better pick and place mechnism but that will be for the next board. One step at a time. The solder paste dramaticly speeds the process of soldering components down on the board and I am quite pleased with the technique.

Populating SMD Components is Slow

2009-02-18T00:21:00.002-06:00

Wow is it slow. I spent most of BDO plodding along soldering down LEDs, resistors and capacitors. I breezed through as many or more through-hole solder joints for the vias in a tiny fraction of the time I spent on the SMDs.

It as slow as point-to-point soldering on a perfboard. I prefer home-etched through-hole boards to point-to-point because of the time difference. If there is a major error in the board it is easy to start over. On a point-to-point board there is a lot of time invested in the assembly.

With my current technique for populating SMDs, I might as well be doing point-to-point. I need to up my game somehow. I'm going to look into solder paste, a reflow skillet and some sort of suction device to manipulate the devices into position.

Toner Transfer

2009-02-15T22:24:00.004-06:00

My skill level is increasing with Toner Transfer. I'm really careful to scrub the snot out of the of board with a Scotch Brite and acetone while wearing gloves. I rinse with only water, still wearing gloves. I'm careful to wrap the board with exactly two layers of bounty. I've gotten the hang of minimum trace widths and separations. I know what I can drill.

Usually, when I go for a dense board, the densest area always gets massive transfer failures. But this time, with all my skills and experience working with me, I transferred a really dense board with very few easily correctable errors. Its pretty darn satisfying to be able to transfer a board like this one.

Transimpedance Amplifiers!

2009-02-03T23:01:00.004-06:00

Thanks to my buddy Tom I have discovered Transimpedance Amplifiers. These chips wrap up the entire functionality of the circuit I was trying to mimic. They work great. A little expensive at $4.50 but worth it. I'm using TI's OPA380A. Digi-Key has them in single quantities. So, I've now quite successfully breadboarded my IR detection circuit and am ready to commit the design to DipTrace.

I learned a little something about FETs tonight. After getting the detector working well, I tried to up the amperage on my LEDs. At some point I pulled the wire off the gate of the FET to connect it in a different way to the MCU. Suddenly my invisible light LEDs became visible light LEDS. Then they turned black and smoke actually escaped the plastic housing! Apparently I pulled the FET just at the moment the gate was charged. Since the gate is a kind of capacitor, it had no way to discharge once I pulled the wire and thus the FET remained on long past 10us. Since the LEDs are only rated for that amperage for 10us at a time, they promptly smoked. Lesson learned! Anyway the 1.32 amps should be fine. I'll just go with that.

Tues Jan 27 RDNO

2009-01-27T23:33:00.002-06:00

Well its been another long time since I've updated. I haven't done a thing with that PS2 controller. Much of my effort has been centered around getting the Milwaukee Robotics Club up and running. The first club contest will be Mini-Sumo.

To that end I've been working on getting a detection scheme working that I saw many years ago in Atlanta on the robot Delta Force. Tonight I got the two high-power LEDs running 1.32Amps for 10us, 300 times per a second. And they didn't burn up! It was tough to get higher than that. I ran them with a variety of current limiting resistors and found that the lower the resistance the less voltage the resistor would drop. I think it is likely that I'm not turning my FET on all the way. They are supposed to be TTL compatible, but maybe just barely. Or possibly the voltage drop of the LED starts to get wonky at these high current levels. Still 1.32 Amps is good enough. The sheet says they are rated for 2 Amps for 10us, 300pps.

The detection circuit was much tougher. I don't fully understand the circuit he is using. I am pretty sure that the first stage is a current to voltage converter and the second stage is a regular voltage non-inverting amplifier. However, there are clearly AC aspects to the circuit and those are a bit beyond me. I think the circuit is designed to pick up the momentary current flow that results when the photodiode changes capacitance due to incident light. On my bread-board I was able to get it pretty much working but with only a half to one volt change with a 1 volt bias. I messed about with the circuit quite a bit to try to get a higher voltage swing out, but all I did was demonstrate my ignorance of the fundamentals behind the circuit. Worse, later I *think* discovered a serious wiring error even though the circuit seemed to have been working. After correcting it the circuit seem to have a strange warbling noise that was not present before. However, the circuit seemed to still function, just with the noise added in. It was starting to get late so I left off.

I think my next step is to either make an etched pcb for the detection circuit or do point-to-point on one of Eddy's nice prototype boards. Bread-boards are super great for messing about with the structure of a circuit. But, they are sloppy. Things pull out of the sockets under the weight of o-scope probes, leads get pushed down and into other leads they are not supposed to touch and there is stray capacitance aplenty. And anyway, as was made apparent to me tonight, I am not qualified to mess about with the structure of this circuit. With a soldered-up etched or point to point circuit I am hopeful that I'll get better results.

PS2 Controller no worky

2008-08-28T12:52:00.003-05:00

Well, last session I got the code into the MCU and got the receiver attached to the MCU. However, I could not get the receiver to respond to my SPI requests at all. A bunch of the session time was spent diagnosing what I was transmitting however. I had the bit order wrong. I was going at the maximum 500Khz which probably wasn't so good on a bread-board with all it's capacitance. I had a code path which didn't manage the slave select properly.

I was able to see all this on Tom's nifty LogicPort usb analyzer. Oh, yea, it took a while to figure out how that software worked too.

However, I worked through all those issues and got what I was transmitting to look pretty good before the session was over. However, still no replies.

I have two things I want to investigate next time:

I am mixing 3.3V and 5V tech here. Now, the logic analyzer was set to 1.5V logic so I would have seen any response from the PS2 controller on the LogicPort even if the MCU didn't see it. However, the notes I'm reading say only some of the PS2 controllers are good at 5V whereas others won't work at all. I need to suck it up and slap down the transistors I need to do the voltage conversion properly. I should also look into using the ATmega48/88/168 which will run at 3.3V no problem. However, the code is setup for the ATmega32 core at the moment and it will take less time to plop down the transistors than switch the code to the newer cores.
One odd bit I noticed about the slave select: it selects long before it sends any data. In fact about half the time the the device is selected, no data is sent at all. Most of that time is before any data is sent. I'm not sure what my code is doing to cause such a delay but I should look into the issue against the possiblity that being selected so long with out data angers the reciever.

PS2 Controller

2008-08-13T17:50:00.003-05:00

Going to try to start blogging regularly again. I think its a good habit. Anyway, I'm working on my Robomagellan again. Towards that project I've been working on communicating with a regular Sony PS2 wireless controller.

When I got the controller I decided that I did not want to bust out the receiver from its plastic case and solder to the connections inside directly. I found a place that sells repair parts for the PS2 console and bought a controller/memory card socket module for $20. There were two controller receptacles in the module and a circuit board. I de-soldered the circuit board and sawed the module in half netting me two sockets. The socket you see above has had junk desktop computer wires soldered back to it and all plugged into a long pin length 0.1" header to make it compatible with a ordinary solderless breadboard. I'll use this to debug the controller interface software I've written. The socket I will eventually mount on to my own custom circuit board for integration with my robot.

Fall Chibotica 2007 at iHobby Expo is finished!

2007-10-24T21:59:00.000-05:00

Well Fall Chibotica 2007 is finally over. Months of effort culminated in a pretty great show. I hope we get invited back. The combat side went the worst in the planning stages and yet they got invited back immediately. Go figure.

Things went wrong during the show to be sure. Chibotica definitely had creeping contestitis. We were so far behind our schedule it wasn't funny. Its a good thing three contests were canceled due to lack of participants. Next year we'll spread it out over both days and maybe even run some some loser brackets during the trade only days.

Scotty and Mike Overstreet have some good footage of the show.

I'll be glad to get back to some regular robot time for a little while. At least until Spring Chibotica starts getting hot. The bi-annual schedule kills me. Calkins wants to do RoboGames once a quarter. I can't even imagine.

Anyway, I want to revive my Robomagellan dreams, do some good humanoid balance and gait work and make a decent Mini-Sumo with my secret weapon. I'll consider myself lucky if I get one of the three done in '08.

RoboGames

2007-07-24T22:49:00.000-05:00

Has it been so long since I've posted? Amazing.

I'm back from RoboGames (long since, actually). It was a blast! So many pictures. I've been so busy with work and trying to organized my own little robot competition that I have neglected my duties here. I won two bronzes at RoboGames 2007. One for Robo-One Wrestling and one for Robo-One demonstration.

I had the opportunity to give Dave Calkins one of our medals in thanks for his inspiration to build our medals in the first place. I hung out with the Robo-One guys quite a bit and even convinced Matt Bauer, a particularly good Robo-One Builder, to come to Fall Chibotica. I'm really going to enjoy going back in 2008! We had four Chibots members there this time! My hope is to go as Team Chibots in 2008. That would be the bomb!

Laboratory Night

2007-05-17T01:01:00.000-05:00

I've decided that my robot building sessions need to be scheduled if I'm to make any progress at all. Usually I just do fits and starts of intense robot building that result in poor robots. I had my first official laboratory night tonight. However, I need to move it to Tues. to align with my gf's late work night.

It should be noted that it is "La Bore A Tory" and not "Lab Ra Tory". The difference is important.

It should also be noted that one can get lab coats with one's name embroidered for about $35. I'm seriously considering getting one. If the night is to be official I need official garb, naturally.

In any case above is the results of my first night. I built this step up converter out of the simple, but not widely available MAX856 and Eddy's new prototype board. Eddy's prototype board is kinda cool in that it some what mimics the layout of a regular breadboard. I wound up with about as many jumpers as one would on a breadboard, but I also didn't need to glob together pads with cold solder. It is a pretty nice board. I had just recently tried to build this circuit with a traditional isolated pad prototype board and, not unexpectedly, it did not work. Who knows where a glob went wrong? This board worked perfectly on the first try.

I'm going to see what else I can cram on the board. I'd like to use it on my upcoming mini-sumo.

Spring Chibotica 2007 a Success!

2007-05-12T23:35:00.000-05:00

Hassenplug brandishes his array of medals, per usual. He actually traded in a first place medal for a third place medal so he could have every color!

Tom W. sports a nice second place medal for his mini-sumo robot, Shadow!

Ryan Myrda sport a second place medal as well.

Mel's granddaughter get interviewed on TV! Mel is hiding behind the purple column to her right.

The pits! Yay! We finally had pits at one of our contests!

Mini-Sumo in action! My evil twin thought it was a good time to take a photo as well, apparently.

Tom G. tries to interview a robot. This went on for several minutes before we finally wrestled the microphone from him.

More Sponsored Material

2007-02-13T09:33:00.000-06:00

The PCBs from Advanced Circuits came in and they look great! Thanks a bunch, Advanced Circuits!

With all the sponsorship so far, the cost of the medal has fallen to $7.81!

I'd also like to thank our other sponsors Rick Buesing, Tom Gralewicz, Terry Surma, Wright Hobbies, Merkursets, Robots Dreams, and once again Atmel.

Chibots Digital Medal

2007-01-18T13:19:00.000-06:00

The design is a success! All five prototype medals worked perfectly on the first try. They look great! With sponsorships and donations the cost is at $12.10 per a medal and is falling as more donations come in. I'm really excited to be able to deploy this medal to the club! I can't wait to award the first one!

2006-12-22T19:56:00.000-06:00

I put the LEDs in and put it in a 1/3 drop resin medal. Red for this prototype. I'll make white and blue medals as well. I ended up going with 180 ohms in the reds after all. That brings them to just at 20mA whereas on the white LEDs its more like 14 or 15mA. The whites actually seem a touch brighter than the red even so.

Overall the effect is wonderful. In the picture the area around the LED is saturated but it looks great in person. Woot!

Success for the Serial Medal

2006-12-22T17:24:00.000-06:00

The very first PCB for the serial medal worked flawlessly on the first attempt! I know it looks a little screwed up in the picture, but that is because of my crappy cell phone camera's very slow shutter speed. Anyway, I am terribly excited! This thing is finally coming together. I need to run out to get resistors for the red LEDs I want to put in it. 180 Ohms works great for the white LEDs but the reds have a much lower voltage drop. And I probably need to snag some 47s for the row selectors as I just had 58s on hand. Although, it looks fine with 58s.

To be certain I need to make up the other four boards and sit on them for a few days to be sure they are stable. Assuming that goes OK the next step will be to finish the work up on the Bill of Materials. I'm pretty sure I'm going to need some sponsorship to get the cost under $15 per a medal. However, I have high hopes for getting the PCBs themselves sponsored which may land me right in the $13 range.

Brazing

2006-12-17T22:21:00.000-06:00

I gave aluminum brazing a shot this weekend. Its pretty cool really. I got a pound of rods from DuraFix. (Check their sales video. Another company that sells the stuff and also has a video is Aluminum Repair.) I also picked up a mapp gas torch kit from a hardware store. The idea is that you get the aluminum up to a certain temperature such that the silver alloy in the rods will melt, but the aluminum itself won't. The alloy act as a sort of metal glue.

It turns out that the metal needs to be pretty clean and further it has to be cleaned the right way. A stainless steel brush was provided with the rods but I soon discovered you really need two: one for pre-cleaning and one for manipulating the alloy while hot. To to make a joint its a good idea to tin both sides.

It also turns out that mapp gas is plenty hot enough to melt aluminum. I slagged a couple of pieces before I got the hang of it. Probably need to back down to propane or even butane.

After around five or six attempts I got a pretty strong joint. Its the one in the picture. I managed to crack the joint open but it's still pretty strong and it took a hell of a beating just to get to that point. To be able to make that strong of a joint with a couple hours practice is pretty cool. Supposedly, after I master the techniuqe the joints will be stronger than the original metal.

I figure this brazing thing can be very useful for making custom aluminum chassis for my robots. When it comes time to make my RoboMagellan bot water tight I think I'll be using this technique.

Anyway I just wanted to do a quick post with a couple links. Sorry its not longer and doesn't share the experience more in depth.

The Serial Digital Medal PCB Layout

2006-12-09T12:40:00.000-06:00

I've also finished the PCB layout for the circuit. I want to fuss over it a bit more, because 5 prototypes boards run me about $95 . Thus any mistake is an expensive one. I'm still kicking myself for the too-small hole sizes from the very first version of the board.

However, the last layout took about a week and a half of work to get it 100% routed to where I was happy. This board auto-routed fully on the second placement attempt. I still needed to do some manual re-routing but nothing too serious. Plus, all the normal lines are 10 mil and the power lines are 15 mil. Each chip has its own 0.1uF anti-noise cap to boot. I'm hopeful the intermittent noise and dust problems of the past will be gone from this design. I'll still probably get it a good solid flux cleaner bath though.

Chances are I'll put PCB layout in today or Monday. I kinda wish I could have them for tomorrows meeting, but that meeting is going to be busy anyway and I absolutely don't wont to rush this. Rushing was a big factor in all the mistakes of the previous version of the medal.

This is starting to get exciting again!

Serial Digital Medal now on ATtiny45

2006-12-09T12:28:00.000-06:00

So the medal is now working off of the ATtiny45 instead of the ATmega32. You can see the 8 pin DIP just to the left of the red dip switch. The display is working great with no glitches. I'm not sure what caused it before but if the problem doesn't come back I should be good. It might have been a loose connection or something. There are a lot of wires for this circuit.

In the picture the text looks pretty bad, but its really my cell phone camera. In real life the display is perfect. I still can't find my good 3MP cannon. :(

If you look to the lower left in the picture you'll see two more ATtiny45's. Those are the two MCUs I bricked before realizing that the programmer was still set to ATmega32. I wondered why the display started out slow and then actually got SLOWER when I set the fuses for a faster clock. Doh! I hope someone in the club with an STK500 can get them back for me.

Serial Digitial Medal working!

2006-12-06T14:07:00.000-06:00

So the problem with the breadboarded serial medal was that the data and the strobe line was backwards and I had shifted the pins connections by one on one of the displays. Nothing that required an o-scope/logic analyzer at all. If I had bother to trace the lines I would have found it. Once I fix the problem the code started working pretty well. Oh well, the device I bought looks fairly neat. At the very least the software is super simple to use.

The breadboard is still using the ATmega32 at the moment but there is not much logical difference in this case. Still, to be safe I will through the ATtiny45 in there before I put the board order in.

Also the display isn't perfect. It does seem to glitch some times on the capital letters. It doesn't look too terrible, but I'd like to figure it out. It seems to be associated with the character rather than a particular location on the display. So it could be the algorithm. Overall it still looks good even with the glitch.

The Serial Digital Medal Design

2006-11-28T13:54:00.000-06:00

So I mentioned before that, to reduce cost and pin count, we were changing the digital medal design over to some serial driver chips. I'd like to talk about the new design a little.

The big cost saver is the ability to use the ATtiny45 (2.13USD Qty: 1) instead of the ATmega32 (8.28USD Qty: 1). Previously, the driver chips that we were using were really just gangs of transistors. Each transistor had an input and output pin. Hence the MCU pin count requirement to operate the chips was high and forced us to the ATmega32.

After some searching our members came up with transistor arrays that, instead of individual transistor inputs feature a clocked serial data input line that feeds into a shift register and a strobe line that latches the shift register bits up to the (now internal) transistor inputs. Additionally the chips feature a serial data out line that leads away from the far side of the shift registers. The source driver, U1 in the schematic and used to select rows in the 5x7 LED matrix displays is the MIC5891. The sink drivers, U2 and U3 in the schematic, used to select columns, are two A6821's.

So in the new design the three driver chips and the MCU are daisy chained: Serial Data Out connects to Serial Data in, one chip after another with common clock and strobe lines. From the point of view of the MCU this forms a single shift register that is 24 bits wide. The first two bytes shifted out become the column selectors and the final byte becomes the row selectors. The idea is for the MCU to clock out three bytes, hit the strobe and then repeat. This basic scheme uses a mere three pins to reset the state of all row and all column selectors and is why the ATtiny45 will work.

Of course, this is just the design. I have the circuit fully breadboarded up and can see the clock, data and strobe lines popping away at the first chip in the daisy chain, but nothing is coming out of the other side of the shift register on its Serial Data Out line. Most likely this mean that something is wrong with the clocked data that the MCU is emitting and thus the first chip isn't properly receiving the data in the first place. I only own voltmeters so it is hard to tell what is wrong with the signal. I've ordered a cheap O-scope/Logic Analyzer from Hobby Lab that should help me out. It should present me with timing diagrams of the signals on clock, data and strobe lines that I can then compare to the example timings in the data sheets for the chips. Hopefully there will be something I can do to correct the signal. My concern is that since I'm using the Bascom Shiftout command, that the only solution will be to shift to C for greater control of the timing. Maybe it won't suck too bad if I really do have to port the code though.

Chibotica Fall 2006

2006-11-13T11:29:00.000-06:00

Chibotica went pretty well. The turn-out was lower than I had hoped for. To my knowledge we only got one person from iHobby Expo. Still, I'm convinced the the Outreach program is the right thing to do. If I can convince the member to have our next fall contest at iHobby Expo, I think we will be quite well attended.

But again the show itself was very fun. The Mini-Sumo especially was dramatic. Its great that Mel's grand-daughter won it. I wish I could have given her a medal as reward. But oh well.

Digitial Medal Super Funness!

2006-11-06T07:36:00.000-06:00

Well, I'm still working on the damn digital Medal. I have one fully working. It looks great actually. (I'd post a pic but I can't find my camera) But of course, we are going to change the design. The board is just not stable. I had one that worked great after construction but then it failed a couple of days later. It improved a lot with a alcohol bath. So at least part of my problem is just dust and debris. I need to buy flux cleaner so I can clean these boards too.

However, my ability to experiment further is limited because I have no good boards left. Basically i can try to repair one malfunctioning board. I will do that, but it won't bring me the confidence that I truly know what is going on with the boards. I am NOT going to order more boards. At $95/five they are just too expensive.

Anyway, another problem with the board is that it is expensive. The massive number of pins required on the MCU means that a ATmega32 is required. However, the MCU can't drive the LED matrix directly so driver chips are required. Some of the members rounded up some driver chips that take a serial input and can be cascaded. This means that the MCU now only needs three pins instead of 22. So we can go from an ATmega32 to an ATtiny45. Its a pretty big savings.

Still More Digital Medal

2006-10-26T10:44:00.000-05:00

Weirdness.

Having missed all my deadlines for the medal I can now relax and go back to the drawing board to get the stupid thing right. I have breadboarded the entire circuit to see where I went wrong.

I got the same sort of weird errors on the breadboard. That's good from a troubleshooting perspective. When I traced it back I came all the way to the MCU pins. Some of the MCU pins can't hold an Active High under any condition except open. The inputs to the ULN2803A are decently high impedance I think. But some of the MCU pins can do it. Others can.

I may have been mis-handling the MCUs the whole time and destroying outputs at random. That could explain what I've been seeing in all my prototypes. I'm going to swap MCUs tonight and see if the symptoms change.

iHobby Expo

2006-10-26T10:42:00.000-05:00

iHobby Expo was pretty cool. Its the largest outreach I've done so far. I learned a lot. The Hobby RC crowd was actually pretty interested in what we were doing. That was a little bit of a surprise. I think we'll get at least a couple new members out of this. Woot!

Disappointment

2006-10-04T21:55:00.000-05:00

Pretty bummed tonight. I got the new corrected PCB boards today as well as the components to populate them. The boards went together easy. No more hole size silliness. I knew already to solder the UDN2981 on the bottom of the board.

However, the board doesn't work. A few columns light up. The best thing I can say is that soft power works. I have no idea of what's wrong at this point and the chances of correcting it by meeting time are slim.

Digital Medal sort of working Part 2

2006-09-21T00:25:00.000-05:00

So, some heat applied to the row seven current limiting resistor fixed the dead row number seven. As for the doubled up column, I've determined that the column is shorted to Vcc on the MCU to transistor array link. That has to be an assembly issue. An unpopulated board doesn't have the problem.

So now the only worry is the soft power. Can it handle the load? Why is it dropping out to two volts in the present circuit? The short doesn't draw that much current, but since I don't know exactly where it is, I can't be sure of its full effect on the circuit.

I'd like to just cut the column signal line to see if I can get rid of the soft power problem, but its really hard physically. Plus there is no guarantee the as to the extent of the short. Maybe I should just test the load carrying capability with a false load? But what if the load is not the real issue? Hmmm. Hmmm. I will have to ponder it for a while.

Arrrr

2006-09-19T14:20:00.000-05:00

My pirate name is:

Black Roger Rackham

Like anyone confronted with the harshness of robbery on the high seas, you can be pessimistic at times. You have the good fortune of having a good name, since Rackham (pronounced RACKem, not rack-ham) is one of the coolest sounding surnames for a pirate. Arr!

Li-ion Batteries

2006-09-18T22:27:00.000-05:00

So today, bored at work, I began to think of the Li-ion batteries I got from Eddy some time back and how I might connect them. A lot of folks just solder the pads, but I kinda wanted to do a removable pressure contact type thing similar to what cell phones do. (The battery is actually intended for a cell phone.) I remember my old cell phone had theses sort of spring loaded plunger style contactors the rear battery door pushed the battery pads onto.

Anyway I went looking for the contactors, thinking they were custom and I'd never find them. I found these .1" Mill-Max spring loaded headers but, having only my faulty memory, felt sure that the battery pads were well over a .1" pitch. To my delight, when I returned home and bothered to check I discovered that my cell phone plunger things looked exactly like the Mill-Max headers and that the battery pads were in fact .1" pitch.

This looks like it will be a cool way to connect my batteries if I can come up with a good way to put pressure on the battery.

Digital Medal sort of working

2006-09-18T22:23:00.000-05:00

Well I made some progress tonight. I have to short out the soft power circuit, but I can get the digital medal to mostly run. One column appears to be doubled up and the bottom row is completely dead. But the text is scrolling! Woot! I'll review the PCB design for the affected row and column, but it could easily be a drilled out hole issue. Its possible that heating the affected pad for a bit will get me a connection.

Anyway I'm happy to have progress.

Digital Medal Struggle

2006-09-18T15:21:00.000-05:00

Sigh. So, the digital medal has problems. Not the least of which is the time and energy I have available to work on it. The worst problem is the damn hole sizes. I trusted the print out as a sort of eye-ball measurement that all the hole sizes were OK. They weren't. I have to drill out a lot of holes. The worst of that is for the LED displays that can't be soldered on both side. I have to drill a second hold very close the pad and run wire-wrap wire through it and the main hole to get a good mechanical and electrical connection to both sides of the pad.

The next problem is the third transistor array that was thrown in at the last minute. I guess I miscommunicated with the fellow who did the schematic for me. I though I had understood him to say that he'd prototyped the circuit. He hadn't done it for this last minute add. First I discovered that power was backwards. I should have looked more carefully once I discovered that. But, no. I started on a second drilled out board only to discover that the inputs and outputs were also backwards.

So now I'm onto to the third drilled out board. Ironically this board is a touch easier because I don't have to cut traces to fix the power. Since the inputs and outputs on the UDN2981 were also reversed, if I solder the chip to the other side it will be connected perfectly on the current board. If this works I don't think I'm going to edit the board except for hole sizes.

Anyway, I should be able to get a bit of work on it tonight. Maybe I'll be able to light it up, who knows. *I WILL* get it working for the November games dammit.

Digital Medal

2006-09-05T22:57:00.000-05:00

Well the Digital Medal Project has been consuming almost all my free time for what seems like a month now. It's almost done! Today I got the prototype boards and tried placing the components. It was designed to be tight. I was astounded when the components snapped into the center hole with the precision that I had measured them for. Its a perfect fit.

All was not perfect, however. The PCB program I used to make the board shows the .02 in holes a lot larger on print out than .02 really is. Either that or the board shop used the wrong size bit. $90 worth of prototype board an I have to drill out half the damn holes and solder on both sides. That going to be a bit of a trick for the LEDs but I think I know how to do it.

Oh, well, the finals should be damn near perfect.

Now to solder up a board and see if the circuit actually works! Boy that it would be amazing to have everything fall into place right at the last minute here. The Table top competition is this Sunday!

Direct InkJet PCB Resist Printing

2006-08-21T19:40:00.000-05:00

So, over on the Home Brew PCB Yahoo group, this fellow, Volkan Sahin, announces one day that he has modified his inkjet to print straight on to copper PCB and gotten it to resist Ferric Chloride long enough to etch. And etch quite fine lines at that. I watched the thread that ensued with considerable interest. Then a little while later another fellow, Stefan Trethan, announces he's repeated Volkan's results. What's more he posts a very detailed description of the printer modification and printing procedure that James Newton captures with fidelity on his Wiki.

At this point I am salivating. I have to have a mod'ed printer like this.

So in this blog, among other things, I will chronicle my efforts to reproduce Volkan's and Stephan's fabulous results.

To begin, I got my C84 off eBay. Less than $30 shipped! The ink kit I got from MIS for $88 shipped. Heh. Still the ink should last a while. I only bought yellow, the stuff reported to resist the best and also a little black. I took a few CCs of the black and put it in the yellow as others had reported they'd done to improve the yellow's visibility on the PCB. Two or three CCs was all it took to turn the entire 4oz bottle of yellow to a dark nasty sort of grey. I loaded all four refillable carts for my Epson with this stuff.

I'm not going to chronicle the assembly and installation of the refillable carts for the Epson as this is a reasonably easy and time-tested procedure that is engineered to succeed. I got it right on the first try and lots more than two people have done it.

Anyway, before I began I wanted to test fire the intact printer on regular paper to make sure it sort of worked. I hadn't gone after the vacuum tube assembly that Stephan assured me I'd have to clean so I wasn't uber hopeful. On the first try, nothing came out. However, I took out the black cart, pulled and pushed the syringe while plugging into the bottom with the priming nozzle, and then reinserted and ran a nozzle clean from the maintance screen.

On the second run I got this:

That would be death for a PCB of course. So a day and another nozzle clean later the printer shaped up:
The black portion of the nozzle test (left slashing lines) is perfect even thought the color pattern is broken. (The color is loaded with the same stuff the black is, so who cares?) And the test squiggle drawn in Paint is un-broken except at the top and left where it was broken in the original Paint file.

Good results seeing as I haven't even touched the vacuum system!

So that is where I stand as of tonight. I have a well-enough functioning C84 loaded with an easy-to-refill ink system. Now I need to embark on the printer mod's described in the Wiki. As ever, real-life intrudes on my hobby. I don't think I shall have chance to do anything tonight as this blog entry has consumed all of my free time. But I shall press on! I can smell ultra accurate etching in my future!

Another Session!

2006-07-31T21:34:00.000-05:00

Woot! Two nights in a row! Still not a lot of progress though. This SPI bus sharing is a little dicier than I thought. Of course I'm making it hard on my self, as usual. I want the bus to multiplex. I want the bus the be able to read data in from one device after I've commanded a second device to gather data and am waiting for it to get the result and pop its READY line. Its a bit tricky keeping track of when the bus is available and when its not. I know that my logic right now is pretty busted. It so busted that I got disgusted and put off fixing it for another night.

I'll come back at it soon and straighten it out.

RoboMagellan Progress (Inchworm style)

2006-07-30T21:39:00.000-05:00

Well I spent a few hours working on the RoboMagellan bot tonight. I didn't get much accomplished really. Much of it was setting up a work environment here in my computer room.. one of two air conditioned rooms in the house. Man it was hot today.

I modified my SPI bus. I put 180 resistors in series with the 3-axis compass. To my delight I found that the circuit still worked AND I didn't have to remove the MCU to drop a new program in. Flushed with success I went to add the accelerometer MCU to the SPI bus as well. Of course there was a problem: all my remaining Mega32's were non-responsive. I had messed up the fuse bits some way or another.

I got KJohn's STK500 up and running and recovered two previously toasted chips via high-voltage parallel programming. This was my second try at this and I was most pleased to succeed.

I added the new MCU behind another set of resistors and tried to program it live. Initially I couldn't. So I raised my resistors up to a few thousand and live programming worked. Then I realized that the other MCU was powered down. Trying again with both MCUs powered up I found the programming cycle got stuck real early in the cycle: during the initial read. Usually I get some error msg form AVR Studio, but in this configuration it just hangs.

I don't have a solution but its not a huge deal since I am using Eddy's Mega32 board and each has an independent power supply. Its a snap to just yank the battery cable on one of them. Still it would be really nice to figure out a circuit that would let me program with both live and both on the SPI bus. I'll just live with for now.

Next session I want to see if I can get some data out of the Accelerometer MCU. Should be interesting going back and forth between two bodies of code to try to get them to talk to one another!

Tilt Compensated Compass

2006-07-28T14:10:00.000-05:00

So, as I posted earlier that the magnetic field here in Wisconsin is mostly straight down into the ground. Normal procedure with a 3-axis magnetometer seems to be: use a multi-axis accelerometer to get the pitch and roll angles of the compass, correct the detected 3D vector, then toss out the Z-component and compute the angle difference between the projected sensed vector and the front of the sensor. However, since most of the field is down, the projection seems to me like it tosses out a bunch of resolution. I'm going to try to write down what I think might be an alternative technique that won't trash the resolution by avoiding a projection operation. (Or at least waiting to project until most of the magnitude is not in the direction of projection).

I first want to define the heading plane in 3D space. This plane is normal to gravity and due north is right along its axis. (X or Y. Doesn't matter.) When the robot/compass is heading due north the sensed magnetic vector points sharply down from the plane, northwards and just a touch west. I'll call this magnetic north. Magnetic North's direction is related to due north's by a pitch angle and yaw angle. If you remove the pitch and then the yaw from magnetic north you then have a vector that is in the direction of due north in the heading plane. Let's remember these rotation operations as unpitch magnetic north and unyaw magnetic north.

In general, when the robot is out and about it is pitched and rolled verses the gravity vector and it is yawed versus the magnetic north vector. The idea here is to rotate the sensed magnetic vector into the heading plane where a meaningful angle calculation can occur between the rotated vector and the due north vector. So if we take our sensed vector and unroll the roll detected by the accelerometer, unpitch the pitch detected by the accelerometer, then unpitch magnetic north and finally unyaw magnetic north the resulting vector ought to be in the heading plane and a simple trig operation can be performed to get the robot heading.

In practice it the result won't be in the plane, but it will be close enough to not worry about the Z-component. One reason it won't be quite in the is that getting the exact value of magnetic north is not all that easy. For the time being I will probably use the USGS predicted magnetic north.

Anyway, this was my effort to type up my thinking on this whole 3-axis tilt compensated digital compass thing. Hopefully it makes sense. Hopefully I can make it work in code.

RoboGames 2006

2006-07-17T08:11:00.000-05:00

Readers 'n' stuff. Weird. I didn't want to post about RoboGames a couple of posts ago simply because I wanted to talk about the magnetometer. I forgot to come back and post about the games. I'll try to make up for it now:

So in June I went to San Francisco to play in the RoboGames. I brought Felix, my new RoboNova and Uno, the vernerable old mini-sumo. As you can see above Felix won 2nd place in the Robo-One Demonstration contest! (Uno got his ass kicked.. he is now retired.) Matt Bauer was kind enough to make a video of Felix's performance. Thanks Matt!

Anyway, RoboGames was quite interesting. Boy howdy its a big event. I'll bet there were 200 or 300 people in the building at once at some points. Anyway, I had never seen combat robots (RC) in person. They are actually quite something to watch. They make one hell of a racket and the noise really pulls on your rubber necker strings. You feel what the spectators in Rome must have felt at the coliseum.

Nonetheless, the most fascinating contests, the ones that I still think about after the contest is over, were the autonomous navigation contests: RoboMagellan and Trinity FireFighting. The whole magnetometer thing below is all about RoboMagellan. I had never actually seen a Fire Fighting Contest. I had heard about them, but they didn't register as being very cool to me. Once I actually saw one and saw that it was really all about indoor robot localization, I became pretty interested. It would be a great opportunity to implement the 2-D-webcam-laser-range-finder concept that I saw at the SRS website and have been itching to do ever since.

The other majorly cool thing about RoboGames were the winner awards. Rather than give prizes as we have done in ChiBots, RoboGames gives electronic medals like the one you see pictured above. I LOVE MY MEDAL! I like it better than any prize I have ever won. At this month's ChiBots meeting I asked the members if they would like to drop prizes and switch over to something like the RoboGames medals. They heartily agreed! So, now we are in the process of designing an electronic medal that is specific to ChiBots. Compared to the Combots logo, our logo is pretty expensive to make so we'll just have to wait and see what it finally looks like, but I'm excited about it!

Anyway, overall I had a blast at RoboGames 2006! There is a pretty good chance I will return next year.

High Latitude Fun

2006-07-17T07:48:00.000-05:00

So I looked some more at the data the magnetometer was giving me. For a while I thought that the X, Y and Z axis might not be aligned the way I thought they were or in the most logical way. The reason I thought that was that the Z-axis was registering some 4 times higher than X or Y. I knew it wasn't a calibration issue because I could re-orient the device that the large reading would move. I figured the large reading HAD to be due north. NOPE! The larger reading on Z was exactly what it said it was: a big magnetic field straight DOWN. WTF, I thought? Localized field? I took the device outside and there was no change.

Finally, after some looking I happened upon the USGS National geomagnetic Program website. They actually have models of the Earth's magnetic field. There is this applet that lets you select a model (they update every five years) a latitude and longitude and the current time. It then dumps out the predicted X, Y, and Z field strengths. Sure enough, the predicted value in Z was 52000 nT down and only 18ooo nT north. I had no idea the Earth's magnetic field tilted so early.

Its good to have confirmation of my readings. It was kind of a eureka moment when I ran that modeling applet. However, after that died down I realized that it kinda sucks a little in that much of the field strength is in a direction I can't use for navigation. Wait. Or is it? Hmmm. Thinking in a post is probably not good. However, just this moment it occurs to me that on the basis of the model I know which direction the Earth magnetic vector is suppose to point. That vector has a simple relationship (two rotation operations) with the "North" direction. That should fact should be usable and allow me to maintain my measurement resolution. I'm having trouble coughing up a sentence that expresses my thinking so I'll stop trying and post it later.

One Day I'll Be a Real hobbyist

2006-07-04T16:06:00.000-05:00

Did some more work at long last. (Oh yeah, went to RoboGames 2006, got 2nd place in Robo-One demonstration but I'm not gonna talk about it). Anyway, I can now talk to my stupid 3-axis magnetometer over the SPI bus. The AVRLib doesn't seem to work so great. I keep dropping back to the examples in the Atmel docs, which work great. The data itself is a bit confusing, but I think that is because the axes may not be align the way I think they should be. I think the x-axis is vertical on the PCB board. Its hard to be sure by using a magnet because the field is so misshapen that it could actually be going a different direction from one sensor to the next. I'll have to figure out how to do a good job testing that.

RoboMagellan

2006-02-22T09:23:00.000-06:00

So last night was a good night. My gf had a girl's night out so I got the whole evening to work on my bot. I added a 2nd story to the frame of the bot a hung the inverted joystick from it. There is plenty of clearance for it with the extra height. Boy it was harder than I expected. I only have a hand drill right now so I ended up using a 1/4 inch bit for #8 screws. Even then, I was all too often misaligned from one aluminum piece to the next. That MircoMark mill that David Cook talks about in his Intermediate Robot Building book is starting to look good. I hate to blow the $900+ or so after shipping and accessories, but I suck so bad at mechanical stuff that I need all the help I can get.

I also put a sentra bottom on the bot. Boy that stuff is hard to cut with a razor knife. Its doable, but I wish I had a better way. A band saw would probably make for a shredded edge. A water knife would probably do great work. I'll check the sofa cushions for some spare change to buy that. *snort*

Anyway, the gf has class though much of the evening so I may get some more work in. I might make some more sentra panels or I might put the wheels back on and wire up the joystick. I's like to see the data output from that thing as the bot drives.

Serial Protocol Driver

2006-01-02T19:43:00.000-06:00

Well I've slogged my way though the skeleton logic of a serial protocol driver for the Linux CPU. I had to learn about Linux semaphores, mutexs, threads and IDEs. The IDE I ultimately chose was Anjuta as I am able to get a limited sort of prototype hint box functionality with it. Its no MSVC but the prototype hints do help once the function has been setup. (I have to put the prototypes for system calls in manually.)

Now I need to make a fake loopback protocol and test the features of the protocol driver. It should never blockup. It should enqueue several requests and return the responses in the order it received them.

It will be nice if it works. This part has been very psychologically hard for me to do because its practically difficult and conceptually simple. Those always pose serious roadblocks for me.

Kalman Filtering

2005-12-06T08:34:00.000-06:00

Been a while since my last post. I've been tinking away on some new C++ code. The old code that ran the GPS experiment is pretty primitive and very specfic. So in preperation for switching over to dead-reckoning I am trying to make some nice clean and fresh code. So far progress has been a bit slow because of the holidyas and a new role at work. However, I have made some nice data types that encapsulate the concept of a robot pose and a kalman float that encapsulates the concept of an associated sigma value and the kalman filtering process itself.

Once I get some fo these basic types I can turn my attention to the basic code flow of the robot: absorb data, compute plan, execute plan.

GPS

2005-11-15T21:16:00.000-06:00

I'm in Atlanta this weekend and happen to be riding in a rental with a GPS. I've been watching the GPS an notice that is occasionally screws up the heading really really bad. It can get completely turned around. Of course, we are amongst sky scraper and the bot is in a park, but the signal strength is still not good according to the GPS. I have my two-axis accelerometer+gyroscope IMU board and I've been studying up on dead-reckoning via encoder. I have even layer out a basic data flow model for a kalman filtering algorithm that incorporates GPS, IMU and encoder. Still, I might yet try to elevate my GPS antenna one more time as I think it may be a while before my current software plans become drivable. Also there is the Builder's Day Out this weekend and I like to have something that is closer to working that what I currently have. :)

First Place Loser!

2005-11-15T21:09:00.000-06:00

The Chibots semi-annual competition was this past weekend. I just brought the ancient Uno in. I really need to finish my other sumo. Anyway, I went up against Black Cheddar in the first round and was knocked out. The bot is so black that my IR sensor can only see if its within 5 or 6 cm. Since there were some many Sumo's they went for single elimination. I thought I was done. Then later they felt bad and had a losers bracket for all the first round knock-outs. Uno won that bracket! So as a grand finale to the Sumo they put the first place winner up against the first place loser! (Me!) Who was first place winner??? Black Cheddar, of course. *sigh* It was a quick death.

GPS Follies

2005-11-06T14:38:00.000-06:00

Bah. I tried the GPS code again. I was pretty sure the turn rate was just too high for what I was trying to do. So I lowered the turn rate and took it out again. Once again I was beset with technical difficulties. The bot ran twice and just sort kinda went in the right direction, but I still wasn't happy with it. To make matters worse, the program would not run everytime. There was some issue with getting blocked on the serial port. I guess either the motors or gps were not responding. Dunno. Anyway, the upshot is that the two times I did run I didn't get log files because I didn't pipe the output to a file. So I don't really know what was going on. I could be that the math is just not precise enough or the heading updates were still too slow or whatever. I don't know and I am ticked that I don't have a way to look back and find out. I should alter the code to directly write to a file. I should also abandon this GPS thing and get on with dead reckoning. I only did the GPS again because it was such a simple change to the code to slow down the turn rate.

Sigh.

Oh well. Back to the drawing board.

The GPS log files

2005-10-31T15:22:00.000-06:00

Well the GPS log files confirm that the data coming from the GPS serial port changes no more often than 1 per a second. Looking back though the newly discovered PDF version of the GPS programming manual I see that it expressly states that the GPS computes a position solution only once a second in its performance spec section.

The turn rate and short (90ft) distance I had the bot going won't do with that kind of update rate. If I want the test program to really work I will need to slow the turn rate way down and probably the the overall speed as well.

I'm not sure if I'll bother since I think I understand the issue pretty well and the time might could be better spent coming up with a new dead-reckoning+GPS based program. The motor controllers are all wired to do closed loop control on the motor velocity. I just have to set the jumper and write a program to set a new heading based on a timed difference in left/right wheel velocity. I could even double check the new expected heading with the GPS.

GPS Navigation

2005-10-29T16:12:00.000-05:00

Well it was a fine day for bottin'! I took the bot out with its new correctly GPS goal and let it rip. It even sorta drove vaguely in the correct direction. However, it did a lot of loop'd'loops and meandering too. I tried speeding up the rate at which I request data from the GPS and the rate at which I controlled the motors but it didn't really seem to help. I haven't been through the logs thoroughly but I suspect that what I'm going to find is the actual content of the GPS messages are not changing very quickly at all. Maybe once every 5 seconds. That is to slow to directly control the robot. I think I will now have to add in a dead reckoning component. I should start thinking about the general mechanism to navigate before I do however. I'd like to avoid writing a big program that has to be trashed because its not architected well enough.

All in all however, I am very pleased to have seen the robot drive around and at least attempt to reach its goal. The fact that the GPS is likely too slow to directly control the robot is a decent experimental result for today. Its is not some technical failing of mine.

Distance Calcs

2005-10-27T20:45:00.000-05:00

Dammit! Just got a chance to review the logs from the last outdoor run. At the time I was mystified as to why the distance to goal function was returning hundreds of thousands of meters. The answer: when you put in your longitude you're supposed to put in negative numbers for western longitudes. Duhhhh. My goal was on the other side of the frickin' world, literally. Jeez. To be thwarted by something so asinine!!! Its dark now, but I really want to take the bot out anyway. I won't but I can't wait for my next chance to do so. It should really work!

Rained Out

2005-10-23T13:44:00.000-05:00

Well I was making good progress until it started to rain. The GPS serial code needed some tweaks. But then when it ran I started getting huge distances to my target way point. So something is clearly wrong with the distance computation code. I'll have to go over it again.

Maze Bot Update

2005-10-23T11:31:00.000-05:00

I guess I should mention that I am not working on the Maze bot until I finish the RoboMagellan bot. Id on't have enought time for even the RoboMagllean let alone both RoboMagellan and Maze. So, the RoboMagellan is the way cooler contest. So that is what I'm going to work on.

Rise from the dead!

2005-10-23T11:13:00.000-05:00

Since its near Halloween I guess it is appropriate to resurrect this blog. Its has been totally dead because all I have been working on is my RoboMagellen robot and its supposed to be a secret. But as the guy who most wants it to be secret is not really adding much to the robot. In fact only Paul, Tom and I have really done anything directly towards the bot, I feel I can go ahead and post here while I wait for my battery to re-charge.

My time is soooo limited its sick. My progress has be horrifyingly slow. I literally steal time to work on the bot.

Anyway, I have some code now that should drive my bot toward a GPS way point. I think I have finally mastered the Linux serial port scheme. It took a while to get it right though. Once the battery re-charges I'm going to take the bot outside and give it a go.

Right now I'm seem to have a custom carrier PCB for my GPS that works despite the need to cut it up all to hell and back because I got the connector backwards. The motor serial code is finally seems to stably command the motor controller. The worst problem is the the very first command after power up always seems to error out. Easy enough to send an initial stop command. I also have Paul's 933Mhz SBC running Puppy Linux and interfaced to the custom PCB that level shifts for the GPS and motor controllers. The code compiles. It has undergone some testing. It really should work.

Wish me luck!

2005-06-26T23:49:00.000-05:00

I forgot to post that my new robot shop is up and running. Its in the basement! I'm hopeful it will mean less clutter since it is not in the computer room any more. Also, as I live on the first floor I shouldn't feel bad running the scroll saw to cut my chassiss. Also I'm making an effort to keep the place neater so that I am not looking at a thirty minute clean up operation before I begin a new project. Lord knows that can stop me in my tracks! Of course, being out 2 1/2 weeks out of the first month I've been in the new place has not really helped. But still I have high hopes.

2005-06-26T23:36:00.000-05:00

So, after a long delay that new maze bot is starting to take shape. The old bot was just too much of a disappointment to continue working on. Nothing I did seemed to help it steer. This bot hopefully has better motors and a lighter weight construction. Also the geometry should be a touch better in the height to base ratio department. I still can't find my postal scale to measure it but it feels lighter.

Tamiya gearmotors to go!

2005-03-16T17:49:00.000-06:00

The higher frequency didn't help at all. It seems to turn suddenly sometimes and I really thing that is related to the increase in resistance to hand-turning the wheels sometimes. You can rotate the wheels easy for a bit, but then it will suddenly get hard. It doesn't do it as much if you rotate the wheels fast, but it sure is noticeable rotating them slow.

I can't be sure that is the problem though. I guess maybe I should wait to get Mike's encoder kits so I can confirm that the speed of the bot is not changing in phase with the speed of the of the PWM. In the mean time I'll investigate mounting wheels to other motors. Maybe the nice ones Tom gave me.

PWM Speed?

2005-03-16T07:20:00.000-06:00

I was looking over a page full of links that Terry posted on Chibots and saw one called something like: choosing the correct frequency for a PWM motor. I popped over and basically it said about 9kHz to 25kHz for motors under 2Amps. I looked up my code and determined that I was using Fast PWM mode with a prescale of 8. At ~8Mhz (internal osc) that comes out to 3.9kHz. The next lower prescale option was 1, however, and that would have put me at 31kHz.. too high. It turned out that I could get a factor of about 2 in there simply by using Phase Correct PWM instead of Fast PWM. So now I can do a prescale of 1 and get a 16kHz base freqency at 8Mhz on the MCU. That's right in the suggested range. The real questions is, will it make much difference to the motors' reaction times? (Assuming reaction speed is really whats wrong.)

It could be that my bot is just too damn heavy. It's like 30oz.

Another thing I can try it to change the gearing on the Tamiya. I'm not sure I have the gears or the manual that tells me how to do that any more so I might have to buy another just for that. I can't remember if I put the gearbox in high-torque or high-speed mode. It was a LONG time ago. Tonight I will look for the box and if I can't find it I will pop over to HobbyTown to get another one before the Sat. BDO.

2005-03-11T18:30:00.000-06:00

Nothing I do seems to have much effect on the behavior of the bot. There is always this long delay before a change in PWM output shows up in the line postion detection. By then it is way too late and the bot is wildly out of control. I am increaseingly convinced that my motors are way under powered for this application. I wish I had some encoder rigged so that I could verify a difference between PWM output and motor responce.

2005-03-10T20:52:00.000-06:00

So Tom gave me these really cool gear motors that I suspect are much better than my plastic Tamyias. With the longer stand-offs for the IR sensor they will now fit on my bot. The issue of course is affixing the motors to the chassis and a wheel to the motor. I'll need a specific radius and width wheel for my IR sensors. How shall I find such a wheel? How wil I also make it match the shaft?

2005-03-05T19:10:00.000-06:00

Well. Niether basic downshifting nor P-only control seems to be able to keep my bot on the line. You can see the big delay in the reaction to the right PWM's downshift. I'm guessing I need to reduce my my P-factor and add in an integral term with maybe some reset rules.

Maze Bot Under Own Power

2005-03-05T15:54:00.000-06:00

Today is a good day. The maze bot is running under its own power!! Right now it is running a debug program designed to get it to follow a line. The Tamiya gearmotors seem to have a lot of variability and even seem to jam occasionally. That really sucks. I may have to ditch them. I hope I can find replacements that will not screw up my geometry too bad.

2005-03-01T21:44:00.000-06:00

Minor update. I've screwed a nice big chipset heatsink onto my 7805. It just gets warm now instead of scalding hot. :) Also got my reversed sensor cables to the MPU fixed. I have calibrated the senstivity for my apartment and am getting good individual detection from each sensor with no light shield. I'm sure perfromance will degrade under flouresents but I can deal with that later. Finally I fab'ed a cable between my MPU and H-Bridge. Just have to connect the motors to the H-Bridge and the wiring on this bot is DONE! I will sure be cool to see it try to follow a line for the very first time. I wish it didn't take me the million years it did to get the bot this far along though. Hopefully some experiance and the BDO facilities will help overcome my various barriers. Anyway, tommorrow its off to Atlanta for two days so no bot stuff. However my gf and I decided to take this weekend easy since last weekend was so crazy. Hopefully I'll get to fire up the bot under its own power this weekend!!

2005-02-28T22:02:00.000-06:00

Some progress on the bot. A simple thing really but big for me because I am so horrible at mechanical stuff. I had planned to go to Home Depot to get the drawer knob but with all the snow I decided against it. So, I tried to canniblize the knob on my CBABot. I'll have to get a replacement from Mike. Anyway to my surprise I was able to find a standoff of almost the exact correct length that fit into the knob! My robot is now balanced pretty well. The sensors are all equi-distant from the ground. Meaningful testing of the bot is coming soon. I can feel it. I just need to put on light shields on and hook up the H-Bridge to the MCU. After that, its all software. :)

2005-02-21T22:07:00.000-06:00

This is a better close up of the working board. You can see three jumpers. One is a forgotten trace, the other two were due to short circuits caused by the mis-alignment of the top and bottom Press-N-Peels. Next time I will keep stuff further appart and try to hone my alignment skills.

2005-02-21T21:53:00.000-06:00

WooHoo! The etched board is a sucess! All the circuits are up and running now. In the photo the debug program in the microcontroller can be seen pumping out the detection state of the IR line sensors over the MAX232 on the etched board. This has left me with a fairly positve feeling about hand etching. I will definately do it again.

2005-02-20T16:02:00.000-06:00

There was a new arrival at BDO this month as well. I'm really sorry I din't get a photo of this fellows bot as it hada giant LCD screen on it. I've never seen such an extensive UI on a mini-sumo bot. There were a few levels of menu that one could click thru via remote control. Neat stuff!

2005-02-20T16:01:00.000-06:00

Well, I forgot my camera for this month's BDO. Nonetheless it was a blast once again. Shown above is the product of my efforts! This is my newly etched power distribution board! It had a few troubles: the sides were not perfectly aligned and that meant that a couple traces that passed near pads got shorted to the pad when I put the component in. Also I left a few traces hitting thru-hole pads on the top side. These were difficult to solder. I learned that I need to use bigger traces, keep traces well away from thru hole pads and only connect to thru-hole pads on the bottom.

2005-01-15T19:12:00.000-06:00

The finished board. It looks quite good! The new board etching station at BDO seems to be a roaring success! I am excited to begin using it so that I can make one-off boards with out so much fuss or expense.

2005-01-15T19:09:00.000-06:00

One of the best ways to spot trouble spots was to look at the press-n-peel. Dark toner appears wherever there was a boo-boo.

2005-01-15T19:08:00.000-06:00

We ironed and peeled.

2005-01-15T19:07:00.000-06:00

Next the pre-cut board is carefully placed between the two press-n-peel sheets.

2005-01-15T19:05:00.000-06:00

Next we tried a two sided board. Here Mike demonstrates his alignment technique. He tapes one press-n-peel side to a perfboard and the aligns and tapes to other side against a light source.

2005-01-15T19:03:00.000-06:00

We then threw the board into the warm ferric chloride and agitated. We check up on it using the white precision board manipulator about every two minutes. Once we saw raw fiber board exposed we started checking about once a minute.

2005-01-15T19:01:00.000-06:00

On our first go around you can see we missed a fair number of traces. Nothing too serious though. All of it could be corrected with a Sharpie.

2005-01-15T18:59:00.000-06:00

For about 2 1/2 minutes Mike applied pressure from the iron on the board.

2005-01-15T18:58:00.000-06:00

Mike carefully places the press-n-peel on the copper board which rest on a sort of industrial paper towel which in turn rests on what appears to be plywood with an MDF surface.

2005-01-15T18:56:00.000-06:00

Here we see a close up of the press-n-peel. You can see that the lines are pretty fine.

2005-01-15T18:54:00.000-06:00

The main attraction of the day was, of course, the PCB board etching demo that Mike and Tom put on for us. In the left you can see the dremel drill press that we used to drill out the holes once we'd etched a board. The blue object is the press-n-peel print out. Right above that you can see some copper clad boards, a coke bottle with Ferric Chloride etchant and a precision white board manipulator. Further to the right, the larger grey box is an agitator. When switched on the top portion would rock back and forth gently. Sitting on the agitated surface is a hot plate and on top of that a plastic tray with some ferric chloride in it.
Posted by Hello

2005-01-15T18:47:00.000-06:00

Tom donated a slew of SMD parts to the club. Since I am starting a library of SMD parts as a part of my transition from point-to-point perfboards to etched board he gave them to me to keep. There are green and red LEDs, diodes and some three pin device that might be a transistor. I'll try to get them cataloged soon. There are probably 500 to a 1000 of each.
Posted by Hello

2005-01-15T18:44:00.000-06:00

I arrived in fine style with my rolling 2 story tool box. I think that little sucker is going to work out! I had two bots a soldering iron and more inside. That coupled with my component carrier that you can just see behind the toolbox makes for a mighty portable little bot station.
Posted by Hello

2005-01-15T18:41:00.000-06:00

An O-scope made an appearance at BDO this time. No-one quite got around to giving it a try though.
Posted by Hello

2005-01-15T18:40:00.000-06:00

Mike had his Therimin bot out and about again. He has two plates in front this time instead of the old antennae. However the sensitivity only seemed a touch better.
Posted by Hello

2005-01-15T18:38:00.000-06:00

Maddie and Don teach Tom his resistor colors.
Posted by Hello

2005-01-15T18:34:00.000-06:00

Well it was BDO time again. I was a bit late this time. Um, unavoidably detained, let's say. Nevertheless, BDO was good fun as always. Here we see some BDO regulars ponder matters 'bot.
Posted by Hello

2004-12-31T07:21:00.000-06:00

You can kind of see the problem. I find these single pad perfboards quite difficult to solder up decently. It is the interconnects that are so tedious and my technique is ugly ugly. And, as I mentioned before... it takes forever. I had another issue like this with a similar type of board, where my max 232 circuit would only work reliably at 110 baud. In contrast I have had great luck tranfering solderless breadboard circuits to schematic-to-layout editors to pro made PCBs. The two mistakes I've made with that technique are drilling holes too small and running tracing too thin for the current I expected them to carry. Both issues could be found and patched pretty easily. The issue is that the PCBs were professionally made boards and expensive. If I can get to the point where I can make my own one-off PCBs for a reasonable cost, I think I will be golden. I'll sure give it a shot next year. Hope everyone has good new year!
Posted by Hello

2004-12-31T07:10:00.000-06:00

Ah, gob soldering at its finest. As you might expect the circuit does not work. The wire nest to back of the perfboard leads 5V to the PCBs on the left and runs thru 180 ohm resistors and thru those ribbon cables on their way to my IR LEDs on perf boards underneath the bot. The PCBs are known to work. I removed the MAX232 and pulled the ribbon cables off the IR LED boards leaving only the red power indication LED in series with the 270 ohm resistor, the 100K ohm Pot, and a cap or two across the 5V and GND lines of the regulator. Nevertheless there is only 44 ohms of net resistance between these lines. A 7805 out of circuit measures about 6K ohms. So, I have a mysterious partial short somewhere. Probably a whisker of a stranded wire or some such just barely making contact. When I add the load of the IR LEDs to this scenario the regulator starts to get hot, even though it maintains its 5V output. But, to add insult to injury 4 of the 16 IR LEDs are not lighting up. Could be related to the same low resistance problem, but I wouldn't be surprised if its not due to a 2nd problem with the circuit. I have yet to locate either issue. This same circuit worked like a champ on the solderless bread board. Sigh. I think I just need to abandon this form of circuit building. Its too prone to error. In the new year I am going to focus on making PCBs. I'm also going to focus on using as many SMT parts as possible. A link to an eBay item was posted on the Chibots mail list, 5000+ SMT style parts, and I snagged it for $31. With PCB making skills and SMT soldering skills I figure I should be able to make monolithic and bot specific, as opposed to general purpose modular boards, easily, inexpensively and avoid most the mind numbing details of board module interconnects. (I never seem to have the parts I need to make a decent, serviceable connection.)
Posted by Hello

2004-12-30T03:48:00.000-06:00

I got this little Zip Zap car as present from work. Its kinda cool. Its got a tiny little motor in it and a tiny little servo for steering. I wonder if I could make a nano sumo with this stuff?
Posted by Hello

2004-12-25T16:08:00.000-06:00

Woo Woo! I got a Robosapian for Xmas! He is a blast! I ran the demos and played a bit with the remote control, but really I can't wait to get him back home and take him apart! They say its a pretty hackable bot. Very exciting!
Posted by Hello

2004-12-23T12:10:00.000-06:00

Adventure!! I remember this game from long, long ago. Brings back memories.
Posted by Hello

2004-12-23T12:08:00.000-06:00

Blast! A couple of teardrop ICs and a 27Mhz crystal is all I get to see. My buddy tells me the unit was only $15 or so. So I guess that is how they keep the price down so low.
Posted by Hello

2004-12-23T12:05:00.000-06:00

Still using the same old five button arrangment I see!
Posted by Hello

2004-12-23T12:03:00.000-06:00

A friend of mine invited me over to his house for a couple days and there I encounterd this intersting little device that I had heard about on slashdot. Its an extra thick Atari joystick that houses enough computational power to run about 7 or 8 of the old Atari games. Games like Centipede, Adventure, Gavitar, etc. It was plain that some of the games had been re-written and had suffered a bit for that. However, on the whole the unit was a lot of fun. Naturally I wanted to take it apart to see what they used to make it go.
Posted by Hello

2004-12-19T15:59:00.000-06:00

This is the same bot with the carrier board inverted. The ghost apparently left the machine in this configuration because the bot kept trying to avoid things we could not see.
Posted by Hello