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.

Brazing

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

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

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!

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.