Sunday, October 15, 2017

Integrated PCB assembled and functional

I got my integrated PCB in the mail last Friday, and spent some time populating it. After fixing some bad soldering jobs and doing a bit of debugging ... it works! The only problem in the board was an incorrect wiring of the on/off switch, which is easily fixed by cutting one trace. The I2C devices enumerate properly on the mux. Here I have not yet populated it with the fancy and expensive pressure sensors, but I did install two of them temporarily to make sure that they are showing up on the bus.

The next steps are to adapt my code to the new board configuration, which should be pretty quick, and expect the 3D printed mounting components, which should come in this week.

Saturday, October 7, 2017

Modified probe design and some 3D printed parts

Pursuant to the flight test dud, I have been redesigning the innards of the probe to fit on a single PCB for reliability so that (a) I don't have to pack a bunch of barewired parts with foam to try to get them to stop rattling, which as we've seen makes them fail; and (b) I don't have a bunch of parts rattling around with a LiPo battery in the probe body.

The new probe looks like this:

The forward support and rear cap for the PCB are being 3D printed. This is how they look, below. Note how the rear cap supports the PCB yet includes a generous cutout for access to the board edge connector and switch, and to expose the on-board temperature sensor chip.

Saturday, September 30, 2017

PCB for airdata probe

After the humbling experience with the flakey bare-wired sensor board, I decided to spin up a PCB that would bring together all the parts I need. This design has only one "loose" wire pair: the wires to the battery, which is designed to be VHB taped and Zip-tied to the board with the loose wires taped up for vibration protection.

The board at Osh Park is here:



Now I need to CAD up some 3D printed components to fix the board in the polycarbonate tube, and expose the rear board edge since that contains the charging connector, the on/off switch, and a tiny little temperature sensor chip (TI TMP102).

The temperature sensor probably should be in the actual airstream, rather than merely exposed on the board edge, but for the time being this should be a reasonable enough configuration for preliminary testing.

Saturday, September 23, 2017

More dreaded electronic crickets

Today, we tried for a test flight with the airdata probe mounted onto the strut of a friend's Cessna 172. Unfortunately, after getting out to the airport, mounting everything, and sitting in the plane, the probe did not seem to be sending any data to the display. We tried bringing the probe within a few inches of the display, to rule out RF interference problems, and turned both parts off and on again, but no dice.

Part of the problem may be that, in anticipation of the test flight, I repacked the contents of the probe to ensure that they did not jostle around during flight. This may well have messed up the circuits in some way and caused this problem.

Tomorrow we debug.

Saturday, September 16, 2017

The dreaded electronic crickets

My greatest dread and fear is of electronic crickets. I put a circuit together, as carefully as I can, plug it in, and ... crickets. Nothing. Nada. Not a peep. Well so it happened today.

I soldered one I2C mux chip and some resistors and capacitors into the board I had made. Soldering the SMTs was not easy, and it's clear that I need at least a good magnifier of some sort and a good pair of very precise tweezers. I then pulled off some signals from the board to see if the I2C mux would successfully mux in a BMP280 pressure sensor breakout board, thus verifying that at least some of the things I put on there were doing their job.

The result was, no detectable I2C presence.

Ok so I imagine the problem is that I failed to tie the address pins (A1, A2, A3) of the I2C mux either high or low, so who knows what address the thing happens to be sitting on right now. This is a pretty elementary boo-boo, and I note (ex post facto as it turns out) that the Adafruit breakout board does indeed tie these pins low, and provides a way for you to override that.

Another boo-boo I made is that, in the mounting for the BMP280 board, I failed to pay attention to the hole diameter -- I ended up making holes suitable for an IC, but not for a (much thicker) 0.1" header.

So I think I have decided to skip bare board manufacturing for now. I'm sure I can learn the necessary skills but that is for another day.

That said, I can still get boards made to mount the breakout boards into -- that will save me from a lot of flimsy and error-prone hand wiring, and will save some space inside my probe.

Friday, September 15, 2017

Perfect Purple PCBs

I just got my PCBs from Osh Park today. I will be populating these for SMD soldering practice, but I'm going to respin this design before I put any expensive components into it.:

  • The BMP280 breakout board I designed it for ships direct from Asia and, though cheap on eBay, mine has yet to come in. Given small volumes, I'm going to just rely on Adafruit's.
  • I missed some connections to tie various pins explicitly high or low, which for what it's worth might explain the problems I had getting my wire-soldered version to work too....

Saturday, September 9, 2017

More partses!

Today the Cloudbase Engineering mount came in the mail, as did a bunch of SMD components I'm going to try to solder to the PCBs I ordered. The mount looks great and is very nicely packaged with really lovely accessories; looking forward to seeing how it fits. As for the components ... yikes. How am I ever going to solder these resistors and capacitors? We'll see.