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Author Archive | Paul Badger

Motion Plug / Breakout board for the MPU9250



Modern MEMS (microelectromechanical systems) are amazing. This chip, the MPU9250 from Invensense, is a 3 axis accelerometer, 3 axis gyro, and 3 axis compass, all in one tiny package. It has an onboard processor for sensor fusion and looks perfect for a quadcopter, home spacecraft, or body sensing. The interface to JeeNodes makes wireless sensing with this board a snap.
The MPU9250 is 3.3V only, so be careful connecting it to a 5V board.

Possible Applications:

  • Tilt-free compass sensor
  • Heading determination
  • Improving GPS accuracy
  • Quadcopter
  • Heading sensing for art projects

In any case, they’re in the shop, and we’re giving away 6 of them with orders over $20. Use coupon code MPU9250

Cold Fusion, LENR and NASA

Screen shot 2014-09-07 at 5.06.35 PM


LENR is now the preferred name for the research that grew out of what is still called “cold fusion.” Cold fusion and LENR are used somewhat interchangeably now, although people realize that “cold fusion” is now a pejorative. This may change back (be changing back now?)  if/when LENR reactions are confirmed. Then scientists may begin to own the (vernacular) term, even though it may eventually be proven not to completely and accurately describe the phenomenon.

After lots of reading about cold fusion (mostly for fun), including experiments, scientific papers and conference reports, my (completely unqualified – because I don’t have a degree in physics) take on the cold fusion / LENR field is summarized below.

  • The effect is real, having been confirmed by qualified, conservative academic researchers hundreds of times.
  • The phenomenon is new science and so is not going to be explained by the standard model,
    although this is controversial, as no theory now convincingly explains all of the experimental evidence that cold fusion researchers have uncovered.
  • Researching the LENR phenomenon is still verboten in academic physics departments, and graduate students are not yet encouraged or allowed to pursue the field, although:
  • Things are starting to change as,  MIT has run a short course on cold fusion in the winter break, for two years running now. You’ll note from the link that the sponsors are Electrical Engineering and Computer Science, and not the Physics Department. Some members of the MIT Physics Department were responsible for spiking claims about cold fusion back when it was originally announced in 1989, and there is still lots of bad blood between the groups of scientists. The Physics Department also has some large grants from the government to study hot fusion, a field that continues to make very slow progress, at the cost of billions of dollars spent.
  • Some LENR researchers have claims of commercial scale power generation (e.g. 1 megaWatt),
  • Which has attracted venture capital, although;
  • Rock solid technical confirmation of the technology is yet to be made public.
  • Patents and proprietary efforts are heating up including one by STMicroelectronics, a name that I expect a fair amount of people who are reading this blog will recognize, as they make sensors for Iphones, and motor drivers among lots of other interesting chips.
  • On the downside, the field attracts some cranks and wishful thinkers, as one might expect with a technology that has been repressed, but also promises many social benefits such as the generation of a fair amount of energy from common materials without a lot of polluting or toxic downside.
  • NASA apparently also believes that there is something to LENR and is putting a bit of money into research, and including it in plans for possible future spacecraft. NASA is all about the future and also all about contingency planning so this may not be saying too much.

Anyway I’ll skip the links and leave you to the “tender mercies of your own Internet Research” as my undergraduate mathematics professor might have said, had the Internet been invented yet. Google LENR and you too can be confused and rewarded.

4 x 16 LCD character display


This is a very high quality 4 x 16 character display removed from new equipment. We bought them on a lark for their ABS boxes, and eventually we will spin up some products for the boxes. In the meantime they are taking up space in the shop and we’d like to move a few out. $5.00.

There are a couple more pictures on the product page.  We found that it works great both with the Arduino LCD library and with our LCD117 Serial LCD drivers.


  • Overall: 3.44″ x 2.37″             87.4mm x 60.2mm
  • Bezel: 3.15″ x 1.57″           81.7mm x 39.8mm
  • Display Area:   2.41″ x .982″   61.3mm x 24.9mm
  • Blue-Black letters on gray-green screen
  • There is no backlight.

In the shop here.

Rev P Wind Sensor Data


The Modern Device wind tunnel outfitted with a pitot tube and temperature sensor.

We wanted some more “objective” methods to confirm the numbers on our growing collection of anemometers, so we naturally thought about pitot tubes. This is the way that aircraft tell their airspeed. I don’t know how much they get used anymore, but the great virtue of a pitot tube is that it can be entirely mechanical, although that would of course depend on the gauge that is used to translate the pitot tube’s pressure into a number.

The pitot tube actually has two connections. The “high side” connection is exposed to the oncoming air and generates a positive pressure. The “ambient” connection, takes into account any static pressure in the system. The two lines are then read differentially, similar to a differential connections for an op-amp, so that the output is the high side pressure minus the ambient pressure.



Isn’t this a wonderful looking set of gauges? These are called “Magnehelic” by Dwyer instruments. They are totally analog (although an electronic one is on top) and are hooked up to the pitot tube with small rubber tubes.

Here is some raw data from the Rev P Wind Sensor at 4 different temperature points.


It would be very nice if static pressure was just proportional to wind speed, but few things in life or in physics are so simple. The pressure generated is dependent on the density of the air, which makes sense if you think about it. The density in turn, is dependent on barometric pressure, temperature and humidity.

Here’s a graph that shows the temperature dependency.

Velocity vs Temp.png001

So I implemented the math to correct for temperature and barometric pressure. One little hiccup was that “Absolute Temperature” was denominated in the little-used Rankine scale (F + 460). Once I entered the correct values for temperature, some wind speeds that looked very plausible came out the other end of my Excel spreadsheet, whose chart looks like this:


A couple of conclusions that I’m drawing is that at lower air speeds, the ambient correction circuit in the Rev P wind sensor is doing an admirable job, for some reason at higher wind speeds there is still some correlation between output and ambient temperature. It’s curious that the higher temperatures are reporting greater output, because normally one thinks of it taking more energy to get cold air up to temperature.

My current focus is on the ambient temperature correction circuit. The thermistor doing ambient correction is a 10k which is not by my choice. I would have desired a much higher value, but 10K was the highest value available in the thermistor line that I am using. The 10K thermistor dissipates about 3mW which is enough to raise its temperature almost 1 degree K, according to the datasheet. (Datasheet is 4mW/K). This would tend to be velocity sensitive also as at higher wind speeds the self-heating would be swamped by the power of the wind speed to enforce the ambient temperature. It’s just a hypothesis at this point.

Another hypothesis is that the “active” (heated) thermistor and the ambient sensor, just don’t track each other perfectly, leading to some variation over temperature. Indeed I would be shocked if there was no variation over temperature. I can cure the self-heating problem fairly easily, but only a lookup table will compensate for the variation in sensor response over temp, and that is the direction in which we are heading.

The new wind sensors are in the shop here: