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Making a Wind Tunnel, Part 1

Screen shot 2013-07-16 at 4.46.24 PM

Constructing a wind tunnel in theory is not a hard thing to do. I first did some internet research as to how I might build a simple wind tunnel, starting on the Internet.

NASA has some links up for educators and I looked through them but didn’t really find much at the level I needed.

Next I used one of my preferred Internet search techniques – doing a Google search, viewing the “images” option, then clicking through to the pages which display promising images: https://www.google.com/search?q=wind+tunnel+construction (The preceding link may be browser specific and may not work for you.)

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By Paul Badger on July 18, 2013.

Wind Sensor Calibration and the Wind Tunnel

Chart

We’ve been selling a little wind sensor, which has found its way into lots of hobbyist projects and even some “harder” science projects including one by the US EPA, but we’ve never had the kind of solid data that would make the sensor really useful for a range of people. We decided that some hard data was long overdue.

At the top of this post you see the plot of wind speed vs sensor output voltage for two different temperatures. Without too much consideration you can see that the output of the sensor is temperature sensitive and that the curve is fairly flat as the wind speed increases. Both of those facts mean that it is fairly easy to confuse a shift in temperature with a shift in wind speed. Or that recalibration will be required when the temperature changes greatly.

Obviously this greatly limits the utility of the sensor, so to remedy this we have a number of ideas in mind, including an Arduino Sketch that uses the temperature output on the wind sensor for calibration and several new schematics and designs for wind sensors.

Before we could do any of that however we had to have a tool to verify wind speed, but not just any wind speed, we needed to be able to precisely control temperature along with wind speed. Building the wind tunnel has been a lot of fun and I’ll cover its construction in several blog posts. I’ll also be posting more data about the wind sensor, as I type up my first handwritten data journals (that look something the image below).

EPSON scanner image

You may wonder about the manual data entry effort. I am worrying about it too, and wondering why I’m not automating all the logging procedures to save the data entry. This is really just the first flush of  excitement at having a research instrument that can provide good data – so there is lots of room for improvement in my technique. The anemometers that I’m calibrating against don’t have any connection to the computer, so if I automate the procedure I will still need to read the anemometers manually and get that column of  numbers in by hand, and also synch it with the other data. I think some kind of semi-automated system still makes sense though. Many experiments can also be done without actually entering any of the data, or even saving much data. More work to do.

So you probably want to see what a DIY research table-top wind tunnel looks like, and I’ll oblige you with a teaser photo just now. Many more details will be provided in the next week, as to the design choices that went into its construction. Yes it does still look like a table full of wires, that aspect kind of comes with designing things as you figure out how to do them. As I decide which parts of the apparatus seem good enough for  my purposes, I’ll harden them up.

WindTunnel

By Paul Badger on July 12, 2013.

More hot-weather discounts

 

July Jee Sale

What, another promotion? To synch our shop with our Dutch collaborators JeeLabs, we’re offering 13% off the entire JeeLabs line of wireless Arduino compatible boards, sensors and displays. Use code JEE2GO to get 13% off of of anything in the JeeLabs collection; that’s anything in  this area of the shop.

The other condition of the “Jee” discount is that you can have to had purchased something else from Modern Device before July, so it’s a bit of a reward for prior shoppers at Modern Device and JeeLabs. We are checking this by hand, so please don’t use the discount unless you have actually ordered from us before.

Note that this promotion runs concurrently with our Deal of the Day promotion (code DOTD) which is 25% deep discount on one selected item, and free domestic shipping on weekends. Whether you select either the JEE2GO promotion or the DOTD promotion, don’t head use the Paypal Express checkout at the first opportunity. You’ll get another chance to use Paypal after punching in the discount code.

Have a great fourth of July and enjoy the fireworks with your favorite cold beverage. The shop will be closed on Thursday but we’ll be up and shipping again on Friday. I’ll be visiting my cabin in the Catskills and attending my friend Ed Potokar’s opening, in Roxbury, NY. You’ll need Google maps to find it.

potoOpening

I’ll also be performing a bit on Friday evening with Ed and assorted other musicians on my new slider synth.

SliderSynthLongLoRes

I worked out the code helping Ed make a similar instrument for a show in New York city. Check out the case made out of white ash. I can’t divulge how much I spent on lumber for this project. The guts are basically an Arduino Mega with our Fluxamasynth board on it. The sliders are linear slide pots sitting on pressure sensors. And a whole lot of code. I’ll post some of the more useful code in the future.

By Paul Badger on July 1, 2013.

Free Domestic US Shipping on Weekends

freeshipping

Starting this weekend, any order placed on a Saturday or Sunday (Eastern Time) will be shipped for free. Anything up to 13 oz. will be shipped USPS First Class; more than that will go USPS Priority. Please note that we’re only offering this to Domestic US addresses at this time. We’re trying this out for the Summer and will keep going if it’s popular.

By Shawn Wallace on June 29, 2013.

New Special Offer: Deal of the Day

We’re starting a new promotion (effective now, June 26th): the Deal of the Day. Each weekday we’ll be offering 25% off a different product in the shop with the promotional code DOTD on checkout. The first deal (for today, the 25th of June) will be the classic Real Bare Bones Board Kit, our popular minimalist Arduino-compatible. Join our Facebook or Twitter feeds to be notified of the daily deal.

By Shawn Wallace on June 25, 2013.

New JeeLabs Blog Series: What If?

JCs-Grid-page-71-604x273

Well, it’s a relatively new series from our friends in the Netherlands that takes a more conjectural approach to learning about electronics. In Jean Claude’s words:

The what-if question is a great way to experiment, especially in electronics and electro-mechanics, because it lets you be prepared and avoid silly (and sometimes catastrophic) outcomes, such as a damaged component, a harmful burn, or even an explosion.

This approach lends itself to all sorts of practical questions:

  • What if I short out a 3x AA battery pack?
  • What if I connect my chip the wrong way around?
  • What if I have to use a 12V power supply instead of 5V?

But also issues as varied as:

  • What if I omit a certain component from my circuit?
  • What if I unplug the Raspberry Pi without shutting it down?
  • What if I wanted to use HouseMon in combination with MySQL?

Power considerations are often the most vexing part of working with electronics, and sure enough that’s where the series starts. The first few posts explore the questions “What if I mix 3.3V and 5V?” (Parts one, two, and three) and What if the supply (to an Atmega) is under 3.3V?“.

It’s a weekly series, so bookmark it, follow the RSS feed, or catch up on the wiki.

By Shawn Wallace on May 13, 2013.

The Othermill, a Desktop Milling Machine with Snap Fit Joints

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Today Otherfab announced a Kickstarter for the Othermill, a unique desktop milling machine. The Othermill is an evolution of the MTM Snap milling machine developed by Otherfab’s Jonathan Ward over the past few years. Otherfab is a small group of engineers and designers within Otherlab, and Jonathan was formerly at the Center for Bits and Atoms. The Othermill comes out of the Fab Lab ecosystem, and is comparable to the Roland Modela in that paradigm.

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By Shawn Wallace on May 8, 2013.

A New Space for Modern Device

It’s a been a long time since we updated our blog since we have been working overtime to get things moved and production back in action. Here are some shots of the new space along with a little commentary.

Dig the clerestory windows. Not commonly found in American manufacturing spaces these days. Nice 18 foot ceilings or so. (I’m guessing.) The space has been rehabbed and is very clean.

We put one of the larger parts bin shelves on wheels, the better to rearrange the space for our open-house party.

Plenty of space for a pick-and-place machine, if we decide to go that way, and the 480 power is already in. Actually that giant box is a transformer with more than a bit of hum. Flip and Sebastian, our production people, never seem to notice (because the sound track never gets that low).

They are jazzed to be able to shut the old folks up in the office and enjoy the tunes. The office also has high ceilings and some great windows, with a mundane view of a residential street. All in all beautiful natural lighting in a very nice office and work space. We can try out some larger projects if we want and generally have a lot of breathing room again. Our old space at the Steelyard had filled to the point that any growth had to occur in the vertical dimension, and even that was looking very crowded.

In the hallway out front of our new home is New Harvest Coffee Roasters, which also maintains a little retail shop in their space. The coffee does not get fresher than this. Yes those are bags of beans in the picture.

The building, called Hope Artiste Village (slightly unfortunate name IMO) is home to lots of small wood and metal workers, caterers, three bakers, a farmer’s market in the winter, several sculptors, along with some live-work space and some office and retail oriented spaces. It’s been fun meeting people and I have a tech swap going on with a wood sculptor already.

All in all, we’re very excited about our new space, which costs about the same as a closet sized one-bedroom apartment in the less tony parts of New York City. We think this space should easily take Modern Device through the next three to four years or more.

By Paul Badger on October 3, 2012.

People Staring at Computers

I’ve dropped some hints on the site that I teach at an art school and am an artist. When Art, Apple and the Secret Service Collide: ‘People Staring at Computers’ is an article about Kyle McDonald’s media artwork People Staring at Computers that caught my eye. Of course it also helps that it has Apple and the US Secret Service are in the title.

In my view what is most interesting about this work is the way the discussion mushrooms outward and the work finds an audience. As the author says, without Apple becoming (remaining?) paranoid and calling the Secret Service, the audience for the work would have been orders of magnitude smaller.

In one sense though, the work anticipates the discussion of the work and both together become the art work. Some artists have referred to creating “social objects” as a goal of their work, and that concept (although I know some readers may find it a stretch) seems very appropriate in this case.

Another irony of the article that remains unremarked is that Apple touts itself as enabling their users to be more creative and supporting artists, and creative endeavors in general. In the real world though (as opposed to ad campaigns), creativity is unpredictable, and not always easily recognized. When faced with something not quite recognizable, most corporations are going to call their legal departments, rather than embrace it. Another artwork that comes to mind along these lines was the apartment that a group of eight artists built in our downtown mall’s parking garage. Rather than celebrating the work, and sponsoring a short exhibition before removing the work, the mall owners just destroyed the work, and legally threatened the artists.

In any case I found this an interesting read. It also explains why the people in the photograph above are wearing Steve Jobs’ head.

By Paul Badger on July 27, 2012.

Pulse Sensor III: Heart Rate Variability

Ways to limit the sources of noise

Where does the noise come from in the Modern Device Pulse / PSO2 sensor? I’ll make a list of some of the places I think noise comes from. Some of these will be supported by experiments to get rid of the noise and others will remain more speculative. The SI1143 chip in the PSO2 sensor uses a photodiode and an amplifier, to amplify the voltage for sampling by an A to D converter.

Sampling on the power line frequency

In my experience, anytime you use an analog amplifier at medium to high gain, in a an indoor environment that contains power lines, the possibility of power-line hum being induced onto your signal has a good probability. This is true even if the devices are powered by batteries – such as a laptop. The field is so pervasive that any nearby amplifier will capacitively couple with it at some level.

One classic way to minimize this power-line noise is to sample on the power-line frequency. This insures that any sixty cycle signal impressed upon on the desired signal is averaged out. It is simple and easy but comes with one very large drawback, it is slow. A power line cycle in the US is 16.666 ms which in terms of a computer’s speed, is basically forever (266,666 Arduino clock cycles for example). Luckily for us, in terms of a human heartbeat, 60 hz is still fairly fast and a human heartbeat sampled at 60 hz or even 30 hz still looks great.

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By Paul Badger on July 12, 2012.