Slow Progress

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

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

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!

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

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

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

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!

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

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

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:

1. 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.
2. 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

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!

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

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

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!

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

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.

Sponsored Material

I got the first of the sponsored material in! 100 ATtiny45's! Thanks, Atmel!

Chibots Digital Medal

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!

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

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.