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.

Friday, September 8, 2017

New try for a mount

The mount I described here turned out to be a #fail. The wood was not shaped exactly like the strut, so it put "pressure points" on the strut that we worried would deform it. I could have continued carving at the wood, but I decided to try another idea entirely.

I have ordered a mount from Cloudbase Engineering. Marc, the proprietor, is super helpful and offers free shipping and a money back guarantee. The Cessna 172 mount will come with a photography-style lockable ball with a 1/4-20 threaded adapter. I made a bogo-machined ("bogo" because it's embarrassingly heavy, but oh well) adapter that will allow me to keep the ball mount set at the same angle, but remove the probe for charging. It uses a RAM EZY-Mount™ Quick Release Adapter Kit to accomplish the snap-on quick release.

Now I'm anxiously waiting for my Cloudbase mount in the mail....

Monday, September 4, 2017

Weighing my probe

My wooden Cessna strut clamp was too tight on the strut, so I figured I would take another stab at the problem. First I must quantify. So to that end, I weighed the probe, found its CG with attachment hardware, and made a few pictures of how it would look mounted relative to the wing strut:

I'm going to shop around the various camera strut mount vendors to see if one of them can sell me something that works out of the box. When in doubt, contact the pros? :)

Sunday, September 3, 2017

Ordered my first PCB

Below is a picture of my first-ever PCB that I've tried to get actually made. This holds three All Sensors Corp. pressure sensors, one 6-pin BMP280 breakout board, and one TC9548A 1-to-8 I2C multiplexer. Along with a bunch of pullup resistors and some capacitors on the power inputs. It has one I2C+power input, and one I2C+power output to an off-board temperature sensor breakout board that I would screw to the outside of my probe.

The cost to get 3 of these made at was just over $20, including free shipping. This work is not on the critical path of any testing at this point. The goals are:
  1. Go through the schematic -> board -> production process.
  2. See what a board looks like in person, and compare it to my design.
  3. Determine how my traces went -- any places where wires are too close?
  4. Show to an experienced friend and get feedback.
  5. Go through it with a multimeter and look for wiring mistakes.
  6. Buy some SMD parts and practice stuffing the board.
  7. With the board partially populated (without soldering in the really expensive All Sensors chips), determine if it actually works.
  8. Get some DIP headers and attach one of the All Sensors pressure sensors, and see if it works.
I'd be pretty surprised if all of these steps went well, but we'll see.

In general, the long-term goal is that I'm trying to develop and "in house" capacity to build PCBs since this will quickly become my limiting factor. I need to be able to miniaturize my work so as to make it (especially the probes) really lightweight, which in turn will make the probe mounting simpler and easier (if it's no heavier than a GoPro, then any little GoPro mount ought to work).

Saturday, September 2, 2017

Sensor board schematics

Working on a sensor board -- this is my first foray into Eagle. The results of today's hacking.

Saturday, August 26, 2017

Tuesday, August 22, 2017

Probe mount saddle

Currently making 3 of these on Shapeways. Random component of an Airball probe. Shapeways is really useful and easy but ... should I buy my own 3D printer?

Sunday, August 20, 2017

Drawing C172 strut profile

I've had these drawing instruments since 1983. Here are two attempts at picking off the C172 strut profile from my profile gage. Use only as directed; your mileage may vary; no warranty.

Sunday, August 13, 2017

Ordered better XBee modules

To those that helped me figure out the XBee modules confusion: I have ordered a pair of these 2.4GHz 60mW ones, and some Taoglas adhesive antennas to go with them, and we'll see....…

Progress on display

Today's (small) Airball accomplishments:

* Fabricated and installed plastic backs for my display units;
* Ordered some RAM ball mounts to attach to these backs, for easy mounting in cockpits;
* Ordered 60mW 2.4 GHz XBee units and Taoglas adhesive antennas;
* Starting to learn Eagle PCB CAD.

The looming task now is to design a fixture for mounting the probe to a pole on top of a car to do some more or less controlled road testing at different alpha/beta values, and in so doing to also see how we're doing on reliability for the communications and for the spurious sensor board freeze.

Tuesday, July 25, 2017

XBee module woes

I have been using XB24-AWI-001 modules for Airball so far. During testing I noticed that if they didn't have line of sight (e.g. if the probe was above the car roof and the display was inside the car), the data would cut out.

Sunday, July 23, 2017

Saturday, July 22, 2017

Go for road test

Road test

No fancy pictures or videos of "flight" testing since we did not have an independent camera person and did not wish to sacrifice safety.

Melissa and I had a pre-flight safety briefing, established the "knock it off" protocol and the chain of command, and went over our test plan and what could go wrong. We conducted some tests, took some data, then returned home and had a quick debrief.

Our main safety issue is that holding a 5-foot pole with a thingey at the end of it is really hard work for the muscles, so any further testing should be done with some sort of mechanical fixture.

On the other hand, holding the pole made me aware of how turbulent the air is. It is not clear if that or my wobbly hold or something else caused the effect, but the airball display was wobbling all over the place. Actual flight testing will determine how much, if any, lowpass filtering we need in the device.

The XBee units seemed to need line-of-sight -- we would lose data if the probe was over the roof of the car. This might require a change in the form factor, e.g., an antenna that you stick onto the side windshield of the airplane. We'll see.

I have yet to determine the stability of my static pressure measurement. I don't think it's really worth messing with right now because the probe body is very poorly sealed. A future, properly sealed probe should give us better information. The ideal of course is that the static pressure remains the same going from zero to cruise speed and back. I'm sure most static pressure sources don't achieve that much, but it'd be interesting to see how well we do.

I have a bunch of data to crunch over the next couple of days and will be posting graphs as I have them. Stay tuned.

Friday, July 21, 2017

Probe noses

A trio of Airball probe noses, fresh from the 3D printers at Shapeways!

Probe innards

On/off switch and panel mount USB port added. Port allows both charging and programming. Probe innards complete; now waiting on mechanical parts.

Thursday, July 20, 2017

Sensor milestones

TWO Airball milestones this evening:

1. First closed loop aero-derived alpha/beta/Q.

2. First battery powered probe.

This is the first time we've put the whole system together and derived actual data from the airflow using the sensor we have designed, and displayed it wirelessly on the display unit we designed.

This is not an *operational* milestone (yet) because we don't have things wrapped up for proper use, but it is a really important technological milestone and means we are almost ready for our first car-borne road testing, followed closely by airborne tests!

Video here:

Sunday, July 16, 2017

Sensor board

Some complete and work-in-progress pictures of the Airball probe "sensor board". This puts all the pressure sensors onto one modular unit with 4 signals going to it: power, ground, I2C clock, and I2C data. This way I can experiment with the "compute board" as I want to without risking damage to my expensive sensors: The stuff you see here is $200 worth of kit!

The soldering could be better as always since I'm a n00b but it wires up properly and works!

Now waiting for 3D printed probe parts to assemble the first functional probe and do a full system test.

Wednesday, July 12, 2017

Breadboarded sensor

Breadboarded Airball sensor probe. Two differential pressure sensors and one gage sensor, all 10" H2O range. One BMP280 barometer. Things of note:

* My 3D printed 5-hole probe nose turned out to be clogged; need to make more.

* The Adafruit BMP280 library for reading the sensor seems to crash whenever I use it with my code. That's sad because the BMP280 is a pain in the neck to read -- you have to download all these calibration parameters from the thing to correct its readings.

Next steps are to figure out if we can get the BMP280 library to work, and to get some more probe noses built so we can try out very simple alpha/beta/Q measurements. And hook up an XBee to the Arduino's serial port to get this information to the display.

Saturday, July 8, 2017

Wireless pressure milestone

Airball milestone: first complete path of pressure signal wirelessly to display.

Damaged board

And now a story from Lamella, the Lame Day of Lameness.

The Sparkfun Fio V3 is an Arduino breakout board that has built-in connections for an XBee wireless module, and can charge a single cell LiPo battery automatically through the USB port. Nifty, eh?

Well so where's to buy a LiPo? It's really expensive to get them shipped, because LiPo, and fire, and stuff like that.

So I went instead to Aero Micro, in Sunnyvale, the well-loved hobby shop. There I had the folks find me a LiPo battery with the correct JST connector on it. They made me buy it before I was allowed to connect it to anything, which turned out to be a wise precaution....

Perry (the well-known proprietor) plugged it into my board, and there was an immediate loud pop. A sliver of something flew off the board and hit Perry in the forehead, alarmingly close to his eye. :( And the magic smoke was released from the board, never to return.

On subsequent investigation, it turns out the JST connector on the battery, while compatible mechanically, was wired with the opposite polarity to what was on the Fio V3 board.

Electronic parts are replaceable, but I'm really scared that Perry could have gotten hurt in this stupid misadventure. I'll have to be careful myself when wiring up new and interesting power electronics together.

Friday, July 7, 2017

Sensor shipment

$150 worth of pressure sensors from Digi-Key. Came in a gift box.