Post 4. Physical Computing chaps.1 &3

Philip Guston, Painter's Head, 1975. Private collection. © The Estate of Philip Guston

Citas:

Introduction:-
How computers see us:

 To change how the computer reacts to us, we have to change how it sees us

/*This also applies to our relation with audiences; the mode of representation we choose conveys a (un)limited way of comprehension and interaction*/

Just in the act of standing up, a person effortlessly reveals

important details through hundreds of subtle and unconscious adjustments every second.

Even though these expressions come and go very quickly, humans have amazing abilities

for reading into this body language the interior state of another person. To make the

computer a medium for expression, you need to describe the conversation you want to have

with (or better yet, through) the computer.

Concepts:

Most physical computing projects (and most computer applications in general) can be broken down into these same three stages: listening, thinking, and speaking—or, in computer terms: input, processing, and output. Breaking down your project along these lines will enable you to better focus on your particular challenges.

Chapter 1: Electricity

Palabras clave: Transducción; Energía

Citas:

 Looking at it from a high level, you’re converting the intentions of the participant into action. At a lower level, you’re converting the physical energy he or she exerts into electrical energy so that a computer can sense it.

 

All electrical and electronic devices exploit the fact that electrons have a tendency to go

from a point of greater electrical energy to a point of lesser electrical energy. You provide

a positive connection (greater energy, or power), a negative connection (lower energy, or

ground), and a conductor through which the electrons flow.

Electrical energy always follows the path of least resistance to ground. The better the conductor, the easier it is for the electrons to flow. The point of lowest electrical energy is the earth itself, which is where we get the term “ground.” 

 The light bulb resists the flow of that energy, converting

it into heat and light. In a well-designed circuit, all the electrical energy gets converted into

some other form of energy by devices like light bulbs, heaters, and so on.

 A switch is a break in the circuit that stops the electrons from flowing. By closing the switch, you close the break in the circuit and allow the electrons to flow again

There are three basic electrical characteristics that come into play in every circuit. The

relative level of electrical energy between any two points in the circuit (for example,

between power and ground) is called the voltage. Voltage is measured in volts. The

amount of electrical energy passing through any point in the circuit is the current.

Current is measured in amperes, or amps for short. The amount that any component

in the circuit resists the flow of current is called the resistance of the component.

Resistance is measured in ohms. Voltage, current, and resistance are all related, and they

all affect each other in a circuit (see sidebar).

 As previously mentioned, a circuit is a closed loop, so all the energy that comes in from the battery has to get used up somehow by the resistance of your load. If your circuit does not use enough energy, it will just go right back into the battery, heating it up, and eventually blowing it up.

 The combination of current and voltage is called electrical power, or wattage. It’s measured in watts. The relationship is straightforward: watts = volts × amps (likewise, amps = watts/volts or volts = watts/amps). For example, a 120-watt light bulb would need 1 amp at 120 volts.2

The amount of wattage you supply to a circuit determines how much work it can do. The more work you need to do, the more power you need.

In this case, you’re using the

change in electrical energy to pass a message

or a signal. For our purposes, this is the distinction between electricity and electronics.

Think of electronics as a subset of electrical circuits that is used to convey information.

electronic circuits don’t need a lot of electrical power. They just need enough power to register a message in a brain or in another computer by turning on small things like an LED or a transistor...

 On the other hand, when you use electrical energy to do physical work, such as turning on motors, you need much more electrical power. For this reason, you’ll find that the input components of your projects will generally need less power than the output components. 

 A direct current (DC) source supplies current on one wire and ground on another, and the voltage between them is constant with the supply wire always at a higher voltage. An alternating current (AC) source alternates the voltage on the two wires. It’s easier to supply electrical energy over very long wires using AC, which is why commercial electrical power is AC. The power coming out of your electrical socket is typically 120 volts AC in the United States and 220 volts AC in Europe and Asia. Electronic components generally operate using DC, however, and at a much lower voltage, typically around 5 volts. They generally need very little amperage as well (less than one amp for most of the circuits you’ll build), so we use AC-to-DC converters and transformers to change alternating current to direct current. The large, blocky power supplies that come with most electronic devices are AC-to-DC converters/transformers that convert the 120/ 220 volts AC to around 5 to 12 volts DC.

How Electricity Flows

 

Electricity always favors the path of least resistance to ground

All the electrical energy in a circuit must be used. Any extra energy will get converted to heat by your components. If there’s too much energy, the components will overheat and stop working.

 All of the electricity follows this path because it’s the only path. In this circuit, the light bulb, which is the only component that uses electrical energy, has to consume all of the electrical energy. In this circuit, the battery, the switch, and light bulb are all in series with each other, meaning that they are all on the same electrical path. When components in a circuit are in series, the current is the same for each of them, but the voltage decreases as each component uses some of it up.

Since the smaller light bulb offers a path of less resistance, some of the current goes through it and some goes through the big light bulb, so both bulbs are a bit dimmer than they would be if they were alone in the circuit. These light bulbs are in parallel with each other, meaning that they are on two different electrical paths in the circuit. When components are in parallel, the current is split between them, depending on their relative resistances. The more resistance a component has, the less current goes through it. The voltage across them is the same, though.

 In this one, we’ve added a bare wire in parallel with the

two light bulbs, as shown in Figure 1.3. Since the bare wire has almost no resistance,

almost all of the current goes through it. This is the dreaded short circuit.

Chapter 3. Building Circuits

We will keep the circuitry to a minimum, just enough to get a transducer’s signal into the microcontroller. Once the signal is in the microcontroller, you can do in software a lot of the logical work that used to be done in circuitry.

The schematic is more abstract than the drawing, which gives you minimal information about each component. The first step in reading a schematic is to decode the schematic symbols.

Conexión de cables, el punto de conexión se llama juntura (junction).

 

Power Sources Schematics

 

Ground Symbols

 

 there are thousands of sensor and actuator circuits available online produced by other microcontroller hobbyists and professionals. You may be tempted to use a schematic or a kit for a standalone device, such as a lie detector or a light organ. These circuits are more complicated than you need because they rely on a lot of circuitry to route, transform, and perform logic on the signals.

Breadboards:

The basic model, with many horizontal rows separated by a central divider and one or two long side rows, called bus rows, is the type that we’ll focus on.

The reason for the center divider is so that you can mount integrated circuit chips, such as microprocessors, on the breadboard.

Breadboard, pins and internal plates.

CAUTION When you start to put components on your breadboard, avoid adding, removing, or changing components whenever the board is powered. You risk damaging your components by accidentally pushing two wires together and causing a short circuit. Later, if you have AC power, or larger DC power, running through your circuit you could also seriously shock yourself. 

It’s best to place your chip toward the top. Generally the lower pins get to do most of the work, and it’s good to have some extra breadboard real estate near them. Make sure that that the legs actually make their way into the hole and don’t get caught on the edge, bending up behind the chip. If you have to take the chip back out, pry it gently from both ends using a flat bladed screwdriver. The pins are easily bent, and the more you bend them, the more likely they are to snap off.

Arranging electronics (Interpreting schematics).

Wherever there is a junction in your schematic, you must join all the components connected to that junction. The most common problems arise when you treat the schematic as a geographic map of what the circuit should look like. The schematic indicates how components are connected electrically. The spatial arrangement of the components in the circuit may not match the spatial arrangement in the schematic, but all of the connections must match up.

Voltage Regulators:

 The 7805 regulator is used to take a varying range

of voltage (from 8 to 15 volts DC) and convert it to 5 volts DC. It can supply almost 1000

milliamps of current (1 amp) at 5 volts, assuming the power supply that’s feeding it can

supply up to an amp as well. The pins of the regulator are numbered from left to right as

you look at the front of it (the side with the label), as shown in Figure 3.19. Pin 1 is the

input pin, which you connect to the 8 to 15 volts of the power supply. Pin 2 is the ground,

which you connect to the ground of the power supply and to the ground of your circuit.

(The metal top of the regulator is also a ground. This will be helpful later when you are

looking for a ground connection to touch with your multimeter probe.) Pin 3 is the output

pin. This outputs 5 volts. Connect this pin to the voltage side of your circuit.

Be neat:

Use cable ties to anchor your power connector (and any future

wire connecting to the outside world) to something stationary on your board. This strain

relief will make it less likely that your circuit will be disconnected accidentally when your

power cord inevitably gets tugged as you connect and disconnect your project. Figure 3.21

shows the right way and the wrong way to wire a board.