Week 4, 9/25: Woodworking

Wood is a lovely and useful material. It comes in a spectrum of hardness and color. It can be worked by machine or hand. It looks beautiful painted or left bare. It lasts long and ages well, it can float or burn, it can be curvy or straight.

Wood and paper both come from the trunks of trees. Trees are plants, and live through a chemical process called photosynthesis. Their cells have a pigment called chlorophyll, which absorbs red and blue light very effectively, and converts the light energy into chemical energy.

Pine is the most common tree for woodworking, though I’m partial to Poplar for boxes. Pine is soft, cheap and attractive. For straight cuts across the grain, the right tool is a hand saw, circular saw or chop saw. A miter box can align 45° cuts for a seamless joint, which look particularly nice with a continuous grain.

There are a number of ways to join the sides of a box. With a miter cut, wood glue maintains the aesthetic. For 90° cuts: nails are the quickest, screws are better if the box needs to disassemble. The more advanced option is a dovetail or box joint with no connectors.

Build a Wooden Circuit Box

1. Go to a nearby hardware store and check out their wood stock. Unless you go to a specialty store, it will be pine. Compare the different sizes and compositions, find something you like. Borrow a ruler, measure the thickness of the board; don’t buy anything yet.

2. On paper, draw your box as a rectangular prism. Use your hands with a ruler as a guide, and figure out what general size box you want. Make sure it can accommodate a microcontroller under the lid. Note Width, Height, and Depth on your drawing.

3. In 3D modeling software, render your box precisely. Account for the thickness of the wood you’ve selected.

4. Consider how to join the sides of your box. Do you want to mitre? Nails, glue, or neither? Remodel your box accordingly.

5. Explode the box model into six pieces and flag the lengths of the unique edges of each.

6. Make a printout for yourself and/or the hardware store. Add ⅛” to every saw line. Figure out exactly how much wood you need.

7. Select an appropriate saw, given your box design and woodworking experience.

8. Cut your wood, get it cut at the hardware store for a small fee (straight edges only), or find a laser cutter (thin wood only).

9. Sand every face of every piece in a circular pattern with first the coarse side, then the fine side of a sanding sponge.

10. Find two metal hinges and a clasp. Attach the lid, keeping it well-aligned.

Week 3, 9/18: Soldering

Soldering is the act of joining two metals together by melting a filler metal between them. The filler metal, called solder, has a low melting temperature. There are many kinds, but we use a lead-free rosin-core solder in class. This variant is non-toxic and self-cleaning. It's important to have a nice soldering iron as well— Weller is a reliable brand.

To solder, anchor one or both of the targets. Tin each target by holding the solder and the iron to the target for two seconds. Then hold the targets together, and apply the solder and iron at the junction. To desolder, apply fresh solder to the joint and use a sucker or wick if necessary.

Week 2, 9/11: Electricity

ἢλεκτρον μαγνήτης

There are four forces that govern everything in the universe: gravity, electromagnetism, and the strong and weak nuclear forces. We'll focus on electromagnetism, which is the law of opposites attracting. The force gets its name from the Greeks, who noticed the peculiar behavior of both amber and iron. Amber— translucent, golden stones of fossilized tree resin— has a more negative charge than the human hand. The friction of rubbing two opposite-charge materials together produces static electricity: valence electrons will jump from amber to finger, building up until released as a spark. Static electricity can cause super-charged surfaces to attract and repel each other (like balloons towards walls, or hairs away from each other). Iron molecules align into poles, which produces the magnetic behavior of iron attracting and repelling itself. The Greek words above, "elektron magnetes", come from the names and stories of amber (Phaeton and Helios), and the Magnetes tribe.

This a diagram of a copper atom. Copper is the 29th element in the periodic table, meaning it has 29 protons and electrons. Electrons orbit the nucleus of an atom in something more akin to a cloud, but we talk about them as shells of varying energy levels. The electron capacity for each shell equals twice the Principal Quantum Number squared. The Principal Quantum Number is both the energy level and the ordinal number of the shell. The innermost shell has a capacity of 2 electrons (2*1^2), the second has 8 (2*2^2), and so on. Because 29 is a number that leaves a lone electron in the outer shell, copper is a very conductive element. That outer, valence electron is easily passed in an electric circuit, which is why most wires are made of copper.

The metrics for each circuit are determined by the chemical composition and sequencing of components. Order doesn't matter for every component in every circuit, but these three metrics— voltage, current, and resistance— must be balanced with every component in consideration. It takes the energy of one volt to move a current of one amp through a resistance of one ohm. Because the units are related to each other in this way, the energy of a circuit can be expressed through an equation known as Ohm's Law: V = I*R, where V is voltage, I is current, and R is resistance.

When we talk about directionality in a circuit, there are a few confusing subtleties. If you're already confused, please skip this paragraph and just remember that current flows from the positive to the negative in a circuit. It's much more common to talk about the flow of current than the flow of electrons, and they're actually moving in opposite directions. Every component has two or more electrodes— the wire terminals that allow you to solder things together. With components that only allow the flow of electricity in one direction, the electrode that collects current is called the anode, and the electrode that emits current is called the cathode. Here's the confusing part: in a battery, the anode is the negative terminal where electrons flow out and current flows in; in an LED, the anode is the positive terminal where electrons flow out and current flows in. The difference comes from the former being a generator and the latter being an emitter.