Dave Termohlen has accomplished much in his 25 years as an engineer, but he may just be hitting his stride with Bitchin' Betty.
Termohlen, a space engineer in Dulles, Va., took home the grand prize and $3,000 in the NXP Cortex-M0 LPC1100 Design Challenge with his low-weight, low-power temperature-controlled variometer and flight logger for remote-control planes.
In flying parlance, these cockpit warning devices are called Bitchin' Betties, named for the often-female voice that warns pilots they're too close to the ground.
Termohlen overcame competitors who used NXP's 32-bit LPC1100 microcontroller to design:
A Wikipedia on a chip
A Vuvuzela-inspired noisemaker that flashed the NXP logo
A faucet sensor/switcher
An energy-friendly socket monitor.
NXP sent out nearly 500 LPC Xpresso boards with to engineers and inventors who passed the first step of the contest, submitted a paper design. From those 500, organizers got back 30 project videos and selected 10 of those for the judging phase.
The idea is to showcase what engineers can do with a part that costs less than a cup of coffee.
"What can you do for 65 cents? Plenty," said NXP Product Marketing Manager Amit Bhojraj. "And that price breaks a big barrier for 32-bits."
Judges gave Termohlen the grand prize for best use of the MCU, good creativity and reliability. Termohlen’s design allows the remote pilot to review the altitude and performance of the plane to optimize things like launch, lift, and landing.
(See his video demonstration and explanation below).
His design—using parts from NXP, AVX, Maxim, National Semiconductor, Measurement Specialties, Panasonic and Cobra—has a simple elegance to it:
The LPCXpresso card polls the variometer for altitude, altitude change (indicating thermal), temperature and battery voltage. It generates speech from .wav data stored in the micro-SD and controls mic-key of (Cobra Micro Talk) walkie-talkie.
An included application allows the user to plot all flight data in MS Excel.
Termohlen wrote in his abstract,
“The system might tell you: ‘Up three point five (feet), at one thousand fifty point four (feet), with four point seven (volts).’ This system could be used in Thermal Duration (TD), F3B, F3J, cross country, or any powered aircraft.”
Total cost? $52.84, much of which (see chart) was the cost of the barometer. Here’s his BOM (check out co-sponsor DigiKey's site for additional information):
ARM Cortex M0
CRYSTAL 12.0MHZ 12PF SMD
CONN MINI MICRO-SD 8PIN PCB GOLD
RES 4.3K OHM CARBON FILM 1/4W 5%
RES 3.0K OHM CARBON FILM 1/4W 5%
CAP .018UF 50V POLY B SERIES
CAP CERM .01UF 10% 16V X7R 0402
CAP CERM .1UF 10% 16V X7R 0603
CAP CERM 18PF 5% 50V NP0 0603
Set of 2 Walkie Talkies (16 mi range)
Termohlen, as you might imagine, is a huge fan of remote-controlled gliders, and therein lies his inspiration:
"I saw something called a Picolario in the early 2000s. While similar in user features, my design uses an ultra-sensitive temperature-compensated barometer for the altitude sensor. This results in an accuracy of better than one foot compared to 1 meter. As soon as I saw the Picolario, I started designing my own version."
Termohlen (pictured) said the LPC1114 showed him "that microprocessor technology had matured enough to fit my application. I feel that I squeezed just about all the power that the LPC1114 has to give out of it."
He's already laying out a new version of the design:
The next version will abandon the COTS walkie talkie, which killed his battery (when transmitting, it pulls more than 10mA).
Instead he's designing in a more expensive but practical 2.4GHz transceiver.
"Splitting the work-load between the transmitter and the receiver will significantly reduce power."
Don't be surprised if the NXP champ's inspiration shows up on holiday gift lists one of these days.
Auto-Pilot: That would take all the fun away. Betty is an enhancer, an auto-pilot would be like letting someone else fly the plane for you. Since I did what I could with 65 cents (an LPC11xx device), there isn't much power or memory left. I'd have to add a GPS and quite a bit more memory. I will add a--very simple--Kalman Filter to Betty in the next generation, but an auto-pilot would require a fairly complex one. I think that I could pull this off with an LPC32xx family device. I digress: These microcontrollers are turly AMAZING. I remember it like yesterday: The introduction of the Intel 8008 and the COSMAC ELF RCA 1802. We've come a long way. While a sophisticated toy, Betty represents a significant enabling technology. Some of the entrants in the LPCXpresso Challenge had some very exciting ideas, they simply unable to follow through to Phase-III. Thanks for the question
The source code (for all phase-II entries) is on the LPCXpresso Challenge web-site (link above).
Trust me, I used almost every trick in the book. I did use look-up based math routines rather than using a standard floating point "power" routine, I used a log look-up routine:
POW = exp(0.19026319L * log(P / 101325.0L));
rawHeight = 14544172.0L * ( 1.0L - POW ); /* Include conversion to feet and mult by 100 */
You'd have to understand the crusty bunch of Glider-Guider old farts (men and women... 95% men) that the name is marketing to. The average age of the folks that would use these things is probably mid to late-40's. Sorry for the offense. I take just as much responsibility as Brian.
Duane, I did give it a lot of thought. My first three headlines were just dull, though. To optimize story visibility, one has to strike a balance between the compelling/provocative and the dull but accurate.
That said, those of us who came of age in the '60s and '70s certainly have language police buzzing off one side of our heads. Yet the propriety that we were taught back then seems, in today's culture, to be completely ignored. It's either true in absolute terms or it's true when viewed through the lens of a guy who's not 25 years old.
And that is a another topic for another post!
I'm going to step out on a style/tact related tangent here. Is it just me, or do other people out there think it's high-time we did away with sexist slang identifiers like "Bitchn' Betty"? I know it may seem innocuous at first glance, and there certainly wasn't any intent to offend, but it and quite a number of other "...ist" slang terms really hearken back to the days when society was free, equal and happy - but only if you fit a certain profile. I don't think it adds anything to the article. The reference to it doesn't seem to do anything other than justify the article title. To me it distracts from what is otherwise a very informative article about a very cool project.
Nice job, Brian,
Have you given any thought to building an autopilot for your sailplane that would automatically recognize and circle in thermals?
Gee, the Measurement Specialties website seems like it's being hammered this morning :-)
Re the pressure-to-altitude conversion - I did some poking through a variety of websites and found several formulae for the conversion - what I'm interested in is how you did this in your software - for example, did you use floating-point and transcendental math, or did you come up with something that simplified the process, like a lookup table? I'm using a fairly small uC, and anything that limits code size would be a plus!