Tuesday, October 9, 2012

Feeling stupid

Spent the entire productive part of the day putting a minimal Arduino on a breadboard.  There's like, 12 components in total, and I still messed it up four times.

About the only thing I did right was to work step by step.

Built a 7805-based voltage regulator.  Which didn't work.  And turned out it was an old problem; my solderless breadboard doesn't continue the power strips the full length.  So a couple of bridges, and now that's working.  But if I hadn't put a "power on" LED I'd still be staring at a dead circuit...

Built the Arduino and it didn't fire up.  Swapped the ATmega168 for a known good one with the "blink" program already loaded on it.  And finally, after staring at the thing for an hour, realized I was holding the Reset low instead of high.  And you don't actually need the pull-up resistor anyhow -- there's an internal pull-up on that pin.

Then hooked up the ISP and kept getting error messages.  Stuck the ISP on to the ICSP header of a working Arduino and confirmed the tool chain was working.  Was basically wiggling parts at random when I thought of pulling off the pin 13 LED.  And that did it.  So why isn't this necessary on a standard Arduino?  What's different about my LED?

Well, finally got to the point where I could hook up the ULN2803 (Darlington Array) and proof the quick-and-dirty solution I had to lighting the VFD; to have it display "00000000, 11111111, 22222222...."  And nothing.  Until finally the niggling little memory of how I wired the robot came back to me and I realized the ULN2803 sinks, not sources!

Which means I can't even do the quick-and-dirty.  Not on what I have.

While I wait for delivery of the Supertex HV5812P-G serial driver chips -- which I haven't even ordered yet -- about all I can do is confirm the LEDs that are going into the Dialight indicator light enclosures are nice and bright, and try to build a capacitance touch switch.  Oh, and I guess I could write a simple look-up table for doing alpha-numeric on my seven-segment vacuum fluorescent display.

I would work on a boost converter, too, but I don't have a nice switching MOSFET or a Schotkey diode on hand.  Nor does Radio Shack really have anything useful there. 

Looks like this project won't be ready by East Bay Mini Makers Faire.  And immediately following the fair I go into tech.  Dangit.  I could have made more progress if I had just a little more cash earlier on.  Like the robot, I've had to make too many design compromises and too many gambles based on trying to work on too tight a budget. 

It is a variation of the Sam Vimes Theory of Economic Injustice.  When you are shy of capital, you have to proceed in ways that are actually more wasteful of funds.  Worst case being, when you can't quite justify the safer, surer, but more expensive route, and gamble on the cheaper route -- which then fails, costing you as much as it would have just to go the expensive way in the first place.

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