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23. Soil and Water Pollution Testing

Robert Bruce Thompson Maker Media, Inc ePub

Youll need the following items to complete this lab session. (The standard kit for this book, available from www.thehomescientist.com, includes the items listed in the first group.)


Centrifuge tubes

Hydrochloric acid


Reaction plate, 24-well

Sodium borate solution, 0.1% w/r to boron

Turmeric reagent


Desk lamp or other strong light source

Paper towels

Specimens (see text)

Water, distilled

Soil and water pollution takes many forms. It may be chemical or biological. The source may be naturalas, for example, when heavy metals leach from a crumbling rock face or scat from wild animals contaminates an apparently pristine mountain streamor the result of human activities such as manufacturing, mining, or even simply doing a load of laundry.

Environmental scientists and technicians frequently test soil and water specimens to determine if they are contaminated by specific pollutants, ranging from specific bacteria, protozoa, or fungi to heavy metals to organic solvents to inorganic ions such as phosphates or nitrates.

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3. Raspberries from Scratch

Cefn Hoile Maker Media, Inc ePub

By Sjoerd Dirk Meijer

You can create your own conductive keyboard out of everyday objects and a Raspberry Pi (Figure 3-1). Follow along in this chapter to learn how to program two games in Scratch, make a homemade conductive keyboard with edible raspberries, and then use your keyboard to play the games.

You don’t need to be an electronics guru to complete this project. It’s helpful if you know the difference between a resistor and a capacitator, but it’s not essential. This chapter will provide you with everything you need to complete this project, including:

Install and configure all of the necessary software on the Raspberry Pi.

Make a conductive keyboard out of a solderless breadboard (or optionally on a stripboard).

Code two Scratch projects: an art project and a memory game.

Let’s start building!

Here’s a list of the components you need to build the conductive keyboard.

A list of necessary materials is provided in Table 3-1.

1x ATmega328P-PU (DIP28) or ATmega8 (DIP28)

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Mark Frauenfelder Maker Media, Inc ePub


As 3D printing explodes, so do the options among printable plastics.

ABS and PLA are the go-to plastics for most consumer-grade 3D printers, but the market is heating up quickly, and the barrier to entry is not very high. New types of plastic, blends of plastic with various additives, and grades of plastic formulated specifically for 3D printing are appearing all the time. With simple tools, it’s even possible to turn pellets or other plastic scrap into usable filament right in your own shop. Our handy chart will help you get a handle on what’s out there at the moment.


Even if it’s technically the same plastic, not all filament is extruded alike. If you find a product from a particular manufacturer that works well in your machine, stick with it!


New filler-blended plastics mimic traditional materials:

Laywood prints lighter at lower temperatures, and darker at higher.

Laybrick prints are heavy, with a surface like hard plaster.

It’s easy to see how Galaxy Blue metal flake got its name.

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8. rotational encoder

Charles Platt Maker Media, Inc ePub

power > connection > rotational encoder

The term rotational encoder used to be reserved for high-quality components, often using optical methods to measure rotation with precision (more than 100 intervals in 360 degrees). Cheaper, simpler, electromechanical devices were properly referred to as control shaft encoders. However, the term rotational encoder is now applied to almost any device capable of converting rotational position to a digital output via opening and closing internal mechanical contacts; this is the sense in which the term is used here. It is sometimes distinguished from other types of encoder with the term mechanical rotary encoder. Magnetic and optical rotary encoders do not contain mechanical switches, are classified as sensors by this encyclopedia, and will appear in Volume 3. They are found in a device such as an optical mouse.

Other related components

A rotational encoder has a knob that a user can turn to display a series of prompts on an LCD screen, or to adjust the input or output on a product such as a stereo receiver. The component is almost always connected to inputs on a microcontroller and is usually fitted with detents that provide tactile feedback suggesting many closely spaced positions. The encoder often allows the user to make a selection by pushing the knob in, which closes an internal momentary switch. Thus, this type of encoder functions as a pushbutton as well as a switch.

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9. Industrial Materials and Methods

Anna Kaziunas France Maker Media, Inc ePub

A materials guide for 3D printing services.

Stuart Deutsch

There has never been a better time to purchase a desktop 3D printer. Nonetheless, they are still too expensive for many users. If you can’t justify the cost of a personal printer, you may be able to access one at a local hackerspace, and there are many online 3D printing services to choose from, including Ponoko, Shapeways, and i.materialise. These companies use a variety of printing technologies to create physical objects from your digital designs and can print in many other materials besides extruded thermoplastic.

Powder bed and inkjet printers use inkjet-type print heads to deposit tiny droplets of liquid binder on top of a thin layer of powder. Once the build platform lowers, a roller spreads and compacts a fresh layer of powder across the surface. The final object is essentially a stack of powder layers finely glued together. Dyed binders can be used in certain machines to produce full-color display models (Figure 9-1). Treatment with super glue and UV protectants can improve model strength and reduce color fading.

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