Categories: all aviation Building a Biplane bicycle gadgets misc motorcycle theater
Fri, 13 Jan 2012
I am ridiculously pleased at this moment.
The new printed circuit board works perfectly! Well, very close, and close enough that I could slap this thing into a case and call it done!
Initial smoke testing (apply power, see if anything goes foom) came back negative, no smoke in evidence. Swapping the ATMega chips around proved to be more troublesome than I'd expected, but careful perseverence paid off. At first, the LCD wouldn't display anything, and I had this overwhelming moment of, "Oh jeez, where do I even start?" I don't have an oscilloscope any more, so I was limited to a multimeter for testing.
Fortunately, the first thing I tested ended up being the problem. The LCD's RW line (read-write? something like that) was at +5v, when it should have been at ground. I checked the layout, and, sure enough, that was the second LCD pin that I had incorrectly routed to power instead of ground. I clipped the wire, jumpered it temporarily to ground, and voila everything worked!
Final tally: two mistakes total, and both of those easily worked around. Not bad for my first-ever PCB design! I've already corrected both pins on the 1.1 version of the design (which will also include an ICSP header). I'm also pondering how this thing is going to get cased, and thinking about going with a premade case for simplicity's sake. That would also mean that anyone else who wanted to build the project would have one less step involved.
Overall, obviously I'm completely pleased. I didn't expect this thing to work right out of the box (to the extent that it does). Aside from two jumpers on the LCD, it's working exactly like I thought it would. When does that happen?
One interesting factor that's pretty surprising is the power consumption. I figured this board would be pulling down 100-150 mA, but even at full backlight, it's only drawing 40 mA at 7-15VDC in. There must be some power-hungry component on my cobbled-together system that's not present in this board (the USB chip is the only thing I can think of), but whatever it is, it's great news! At 40 mA (call it 50 for a bit of safety-factor), a set of 3AA batteries would theoretically power this thing for 50 hours! (Not really, of course -- once the voltage drops below about 4.3, it'd probably stop working.) Any vehicle's electrical system will take this load without even noticing it. Just shy of .03 watts! That's not a typo; point-zero-three.
I can't wait to get this thing in a case, although that is a completely different challenge, and one which is roughly commensurate with making the electronics in the first place, depending on how I go about it. I'm just amazed that it works, and so pleased I can call it "good enough," and move on to the next phase!
Posted at 22:11 permanent link category: /gadgets
Categories: all aviation Building a Biplane bicycle gadgets misc motorcycle theater