Thursday, December 24, 2009
NES Arduino PCB - v0.2
The new revision grabs the Arduino ground off the board which eliminates that extra wire. I also chained together 2 shift registers to make use of all of the Arduino digital outs. So now the board has 14-bits of control through a single NES port. I'm using some new 1/2 oz copper boards and they give a nice clean etch! I dig the clear board too.
Well I drilled the board (almost destroyed the last pad too), soldered everything together and popped in the two ICs. I crossed my fingers and turned on the NES, loaded up my test program and... no joy. I did notice a strange humming sound coming out of my TV, so I did the usual sanity checks. The first chip felt pretty warm, so I unplugged the board from the controller port, and I noticed that the humming went away. I had a hunch that there was a short somewhere, I could only hope that it wasn't in my design.
Let me just say that a continuity tester is key for diagnosing these issues, you can make a simple one with an LED or make sure that your multimeter has the option. Even budget ones have this feature, mine (<$15) has an audible one, which is really handy. I started poking around, and I noticed that two pins were conducting (none should in this design!). Bastard! It's the first time I've used a ground plane fill for a board, you'll notice in the board layout below that a lot of the areas are solid. This saves on etchant and gives a clean look to the board. I guess I got sloppy though, I traced the path and found a splash of solder between VCC and GND. Yikes, I shorted the power lines. I was able to clean up the trace without much of a problem. I wired everything back up and it worked perfectly. Whew!
Finished (working) board, I'll extend the test software to 14-bit tomorrow.