Dammit, Molex

A project log for PIC-On-The-Go

PIC Microcontroller dev boards, in unusual cases

JarrettJarrett 04/17/2015 at 16:490 Comments

I built a really really cut down version of this, using the limited amount of parts that were kicking around my hackspace.

There were some compromises made.

I populated all of the headers, the USB connector, and the DIP socket. The decoupling cap C2 and the pull-down R1 is on there, too.

Notice that the USB footprint is kinda terrible. The signal/power traces were too short, so I had to shove the connector in towards the board a lot more, which meant the mounting pads didn't line up anymore. Bah.

The protection circuitry, F1 and L1, are both substituted with jumper wire because I'm sketchy like that. Protection diode D4 is left off entirely. The 3.3V power supply is also absent.

The SMD LEDs were replaced with small through-hole versions.

I didn't have a good switch, so it had to be replaced with this one:

Due to its pinout and orientation, the bottom is the only place it could work in order to not have interferences.

A reminder: This is an in-between project. I totally don't care about it! I only need something that is marginally better than a breadboard, because having to wire that up every time sucks.

After all of that, I plugged it in, and... Nothing. My PIC programmer wouldn't read anything, and all of my test gear at home is in storage (because I prefer to come into the hackspace to use their's, now). As I was doing this, I was making dinner, so I went off to handle that for a bit.

Later, came back to my board. "Is something burning?"

My microcontroller was very toasty. After unplugging it (very very quickly), it got dumped off to the side for a few days until I had time to troubleshoot.

Totally coincidentally, this was about the time I finished another PCB for a different project. As I was looking around in Altium's 3D view, I noticed something a little bit off.

Yup! The 3D model is flipped, clipping through the board. A short internet search later, and sure enough, the Molex-supplied library component has its pins in the wrong order. If you look back a few project logs ago, you can juuuust see that the current project has the same issue.

Molex, you are terrible.

Quick fix:

That right there is a very dangerous thing. A polarity-changing USB extension cable. But it works for this! I have a blink sketch going.

Marking this project as complete for now, but eventually I will get around to testing the power supply, etc. Then do a new run of boards with revisions. I'd like to add mounting holes and improve silkscreen positions, too.