# Status

This is written from the perspective of a hobbyist, electrical engineers and designers still design basic components and the level of detail of their knowledge is a deep as ever, probably deeper. But for the hobbyist things are simpler. A workshop that SCIL is thinking about offering.

# General

Electronics has changed in the age of the Arduino, not just because of the Arduino but other things have also contributed:

• Most electronics now have micro controllers and software
• While discrete components still exist much work is done with sub assemblies often containing 100's of components.
• Prices have fallen.
• The web provides almost real time access to components and other gear.
• Specifications that used to require ownership of manuals are now online.
• Tons of learning material online.

# Theory

## Then

In the old days electronics was taught from a theory of basic components:

• Batteries - source of dc voltage
• Resistors
• Series and Parallel Circuit.
• Network theory
• Current
• Capacitors
• Inductors
• Transistor
• ......
• Complex circuits
• AC theory.....

## Now

• Components are often modules, these may have 3 sets of connections, power, input, and output
• Need to understand voltage, current, and power.
• Need to understand the relationship of inputs and outputs of black boxes

# How To Build An Amplifier

## Then

• Find plans or design a power supply
• Find plans or design an amplifier
• Make parts list and order.
• Build and debug.
• Tens of parts.

## Now

• Order an amplifier and power supply ( must know how to select appropriate parts )
• Connect amplifier to power supply
• Two parts plus wire.

# What to Learn

Now you still need to know the basics of Voltage, Current, and Power, this is perhaps best understood by using the analogy of electricity to water and water pressure: ( link needed ). Rather than think of AC and DC it is probably best to think of these as quantiles variables that change with time. DC is just a Voltage that is constant, and therefore the simplest, to understand.

Next think of other circuit components as "black boxes" that have some practical use, and for now ignore how they work. The old basic components: Batteries, Resistors, Capacitors, Inductors, Transistor.... are just examples of these black boxes, but perhaps not the place to start as you can easily buy much more interesting ones for cheap money.

In the new world we need to think of the power/load characteristics of "the black boxes" and the communications between "black boxes"

### Spend Time On

• Basic concepts of Potential Difference ( Voltage units Volt ), Current ( units Ampere ), Power ( units Watts ) Charge ( units Coulomb ) Time ( units second )
• Basic ohms law, but note that it is not a law for many components, perhaps most. Is good for metal like wires and resistors.

### Spend Less Time On

• Series/Parallel Circuits - except to know in series circuits the current is identical for all components, in parllel circits the voltage is the same for all components.
• Resistor Code - skip it use a meter.
• AC Impedance Calculations

# Theory Details - Things to Learn

The following is an outline things you might want to learn, it is not an in detail explaination but might be a useful guide to what you already understand and what you might want to learn.

## Rock Bottom Basics

### Charge

Most matter is loaded with stuff that is charged. Charge is a physical characteristic of some matter that can exert a force on other matter that also has charge. Charge comes in 2 flavors, we could call then red and blue, but instead we call them positive and negative. Like charge repels and opposite charge attracts. The force of attraction is typically very strong so most charges are paired up with a nearby opposite charge, this gives a total charge of close to zero and so the charge is neutralized and may not be noticed. Atoms consist of a center the nucleus which has a positive charge and a cloud of electrons around it. Typically the electrons balance the charge of the nucleus. When the charge is not balance it may be because an electron has be transfered to a nearby atom. One atom is then positive the other negative so the electric force holds them together and we have a type of atom. Understanding electrons and there orbits around nuclei is a triumph of 20th century Physics and Chemistry and in principle explains all of chemistry. But that is not our story.

Electrical units are much more closely tied to the Metric or SI system of units than the English System. Charge is typically measured in units of the electron's charge ( Physics ) or Coulomb ( Physics/Electronics ). The electron charge = xxx Coulombs. One Coulomb = xxx electron charges. A liter ( more or less a quart ) of hydrogen ( our simplest element ) under more or less normal pressure and temperature contains Coulombs of positive charge and of negative charge for a total of 0 charge.

The algebraic symbol for charge is Q ( not C though that would make some sense ).

### Potential Difference

When you move a charge from one place to another you may have to work against forces from other charges. The amount of work in moving from one place to another ( per unit charge ) is called the potential difference. In the metric system work is measured in a unit call the Joule. Potential difference is Joules/Coulomb a term that may be new to you, but it has another name the Volt, which you may have heard of. Batteries are made so that they have a potential difference between it two ends ( called poles ). Because Potential difference is measured in Volts it is often called Voltage.

Keep in mind that voltage does not exist at a point but is the difference between two points.

### Current

Potential difference exerts a force on charges. This can make them move. Often this takes place through a wire or other object. The amount of charge that moves through an object ( or past some point or boundary ) in that object per second is called a current. The algebraic symbol for current is often I. The units for current are ( Coulomb / second ) = Ampere.

Unlike voltage that is measured between two points, current is measured at a point. Often to measure current we need to break a circuit at a point an inset a meter there.

### Resistance

So lest think of a Potential difference from a battery across the two ends of a long peice of wire. Typically the charges bump into obstacles which slow them down. So the result of that is that larger Potential differences move more charge per unit time, or larger voltages produce larger currents. In the simplest case that relationship is linear I = V * ( some constant ) That constant ( for situations where the relationship is linear ) is 1/R where R is called the resistance. The linear relationship is call Ohms law. The units for R are Ohms.

Not all circuit elements obey the linear relationship, Ohms Law. When they do they are often called resistors. When they do not they may be called non-linear. Non-linear components may be represented by a graph of the relationship between voltage and current.

Electrical energy is typically used in 2 way: to carry data ( wifi, telephone, sensor readings.... ) and to carry energy = power * time. Even when used to carry data there must be some power/energy used. The term load is used when device A which has a power source is connected to device B which uses some of that energy. Device B is the load ( what is being "carried" ). When connecting device B the load we want to make sure we do not over load device A. If we want a battery to last a long time we want as "light" a load as possible. The amount of load may be measured by treating it as a resistor or other component, or by specifying its voltage/current characteristics, or by specifying the power it draws form the source.

## Constant Voltage

Most circuits are set up as constant voltage. By that we mean that for some time the circuit operates with some voltage constant. Here we will consider it constant even if it is constant for a short time as with a pulse, which while varying is constant first at one voltage and then at another. We often think of voltage as the cause of other things like current. This is fine, but really we should just think of voltage and current being linked by some relationship. We could think of the current causing the voltage.

### Output

A simple constant voltage output might be a simple battery, say a 9V battery. It is called a 9V battery because under reasonable load for a reasonable time the voltage is 9V. When we connect it to some other component ( called the load ) current starts to flow. This requires that power from the battery be transfered to the load ( power = voltage * current ). We can measure how "heavy" the load is based either on the current or the power. What is a reasonable load depends on how long we want the battery to last. So for a battery a reasonable question is what is a reasonable load ( we will not answer this here ).

## Communications

Parts of circuits communicate with each other. In the old days this was mostly by sending a voltage from one part to another. Now we still mostly use voltage but it is coded. Signals typically depend on time so over time the signal changes.

### Analog

The signal to be sent typically is just a voltage and the amount of voltage is the signal. For example a temperature sensor might convert the temperature to a voltage proportional to the temperature. We still use this method.

Here the ......