D-meter updates

I’ve been able to do some more work on the divergence meter now. The university’s labs made short work of the surface-mount soldering, but there were some hitches in the assembly and testing phase, in which I discovered some of the part footprints were wrong, and it was a bit of trouble getting the programmer working.

I was able to work around most of the bad footprints, but some of them were barely salvageable, since the through-holes were too small. I was able to drill them out on the drill press in the lab, but that left me with very small contact areas to solder to, so I had a few hideous solder joints.

After getting the power supply portions of the board soldered came getting the MSP430 talking to my MSP430 Launchpad, which I’m using as a programmer. Initial attempts to program the micro were met with silence (and mspdebug reporting no response from the target), but the problem turned out to be due to using cables that were too long- I had simply clipped test leads onto the relevant headers, yielding a programming cable that was around 1 meter long, while the MSP430 Hardware Tools User’s Guide (SLAU278) indicates that a programming cable should not exceed 20 cm in length. I assembled a shorter cable in response (by soldering a few wires onto the leads of a female 0.1” socket) and all was well.

The most recent snag in assembly was the discovery that I had botched some of the MSP430’s outputs. I had connected the boost converter’s PWM input to Timer A output 0 on the micro, but I discovered while writing the code to control the boost converter that it’s impossible to output PWM on output module 0, due to the assignment of SFRs for timer control. The user’s manual for the chip even mentions this, but I simply failed to appreciate it.

I could have cut a few traces and performed a blue wire fix, but it seemed like a very poor solution, and I was still concerned about the poor contact on the other vias I had to drill out, so I bit the bullet and created a new revision of the board with correct footprints for all the parts, and a more comprehensive ground plane (hopefully reducing inductive spiking on the optocoupler control lines). I’ve now sent revision 1.1 out to be made, so improved boards will be here in a few weeks. Until then, I’ll be working on the software a bit more, and hopefully updating this post with photographs.