Getting Started in Electronics by Forrest Mims

• You cannot see electricity. You see its effect.
• All matter has electrical properties.
• The best way to understand the nature of electricity is to examine the smallest component of every element, the atom.
• Electrons have a negative elect rial charge.
• Protons have a positive electrical charge.
• Neutrons have no electrical charge.
• Normally an atom has an equal number of electrons and protons. The charges cancel to give the atom no net electrical charge.
• It's possible to dislodge one or more electrons from most atoms. This causes the atom to have a net positive charge.
• Free electrons can move at high speed through metals, gases, and a vacuum, or they can rest on a surface.
• A stream of moving electrons is called an electrical current.
• The electron is named after the Greek word for amber!
• A fundamental rule of electricity is like charges repel and unlike charges attract.
• Remember: Unlike charges attract. Like charges repel.
• Electrons travel through some materials but not others.
• Materials through which electrons travel are conductors.
• Materials through which electrons travel poorly or not at all are called insulators.
• An immobile static charge flows through a conductor as an electrical current.
• Electrical current flows from a region of high charge or potential to a region of low potential.
• A current flowing through a wire creates a magnetic field around the wire.
• Current is the quantity of electrons passing a given point. The unit of current is the ampere.
• Voltage is electrical pressure or force.
• The work performed by an electrical current is called power. The unit of power is the watt.
• Conductors are not perfect. They resist to some degree the flow of current. The unit of resistance is the ohm.
• Ohm's Law: V = I x R
• Electrolytes are chemical solutions that contain many ions.
• A current flowing through a conductor establishes a magnetic field around the conductor. This effect works both ways so that a current will flow in a conductor which is moved through a magnetic field.
• If a junction of two dissimilar metals is heated, a current will be produced.
• Alternating current (AC) is usually produced by rotating a coil in a magnetic field.
• AC voltage is usually specified at a value equal to the DC voltage capable of doing the same work.
• AC is better suited than DC for transmission through long distance power lines.
• A wire carrying AC will induce a current in a nearby wire. This is the principle behind the transformer.
• The multi meter is the single most important electronic test instrument.
• Electricity can kill!
• An electrical circuit is any arrangement that per mites an electrical current to flow.
• When a wire or other conductor is placed across the connections of a component, some or all of any current in the circuit may take a shortcut through the conductor.
• The human body conducts electricity.
• Electronics is the study and application of electrons, their behavior and their effects.
• A pulse is a sudden, brief increase or decrease in a current flow.
• A signal is a periodic waveform that conveys information. The process that generates the waveform is called modulation.
• All electronic devices and circuits generate small, random electrical currents. When these currents are unwanted, they're called noise.
• Always use wire rated for the current it is to carry.
• If a wire is hot to the touch, it's carrying too much current.
• Mechanical switches permit or interrupt the flow of current.
• A relay is an electromagnetic switch.
• A microphone converts sound wave vibrations into corresponding variations in an electrical current.
• You can almost always use any value [resistor] within 10 or 20% of the required value, so go ahead and use it.
• There are many kinds of capacitors, but they all do the same thing: store electrons. The simplest capacitor is two conductors separated by an insulating material called the dielectric.
• The ability to store electrons is know as capacitance. Capacitance is specified in farads.
• The capacitance specified for most capacitors may be from 5 to 100% away from the actual value. Therefore, you can often substitute close values for a specified value.
• You must make sure the capacitor you plan to use meets or exceeds the required voltage rating.
• Capacitors can store a charge for a considerable time after the power to them has been switched off. This charge can be dangerous.
• Resistors and capacitors are the key ingredients of many electronic circuits.
• The product of R and C in these [integrator/differentiate] circuits is called the RC time constant.
• Electrons moving through a wire cause an electromagnetic field to encircle the wire.
• Coils resist rapid changes in the current flowing through them while freely passing steady (DC) current.
• A high voltage pulse can be produced in a choke when the current flowing through it is interrupted.
• Transformers have the ability to transform voltage and current to higher or lower levels.
• The ratio of primary to secondary turns determines a transformer's voltage ratio.
• Note: Leads of transformers are color coded.
• The most exciting and important electronic components are made from crystals called semiconductors. Depending on certain conditions, a semiconductor can act like a conductor or an insulator.
• Doped silicon has very useful electronic properties.
• By forming some p-type silicon in a chip of n-type silicon, electrons will flow through the silicon in only one direction.
• A diode will not conduct until the forward voltage reaches a certain threshold point. For silicon diodes this voltage is about 0.6 volts.
• Too much reverse voltage will cause a diode to conduct in the wrong direction.
• The zen er diode is designed to have specific reverse breakdown voltage. This means zen er diodes can function like a voltage sensitive switch.
• Amplifiers let a little force control a bigger force.
• There are two main families of transistors: bipolar and field-effect.
• Most microcomputer and memory integrated circuits are arrays of thousands of misfits on a small sliver of silicon.
• Power misfits allow a few volts to switch or amplify many amperes at very fast speeds.
• There are two families of thrusts, silicon controlled rectifiers (SC Rs) and Tracks. SC Rs switch direct current and Tracks switch alternating current.
• Light is composed of particles called photons that behave like waves of energy.
• Photons are produced when an electron that's been excited to a higher than normal energy falls back to its normal level.
• As kith from a very small source spreads outward, its intensity is inversely proportional to the square of the distance.
• The light emitting diode (LED) converts an electrical currently directly into light.
• The light emitted by an LED is directly proportional to current through the LED.
• LED's can both emit and detect light.
• All transistors are light sensitive.
• Solar cells are NP junction photo diodes with an exceptionally large kith sensitive area.
• Electronic circuits can be made by simultaneously forming individual transistors, diodes, and resistors on a small chip of silicon. The result is an integrated circuit.
• No matter how complicated, all digital integrated circuits are made from simple building locks called gates. Gates are like electronically controlled switches.
• The "not" gate is usually called the inverter.
• A binary 0 or 1 is a bit. A pattern of 4 bits is a nibble. A pattern of 8 bits is a byte.
• Binary numbers can be sent through wires (buses) all at once (parallel) or a bit at a time (serial).
• The voltage drop of diode gates means amplification is required in order to connect together a series of gates.
• Three-state inverters and buffers have an output that can be electronically disconnected from the remained er of the circuit. The output is then neither high nor low. Instead it "floats" and appears as a very high Resistance.
• Combinations logic circuits respond to incoming data almost immediately and without regard to earlier inputs.
• Virtually any combinations circuit can be implemented with only "band" or "nor" gates.
• The output state of a sequential logic circuit is determined by the previous state of the input.
• The sequential logic building block is the flip-flop.
• Individual gates require 3 or 4 millipedes.
• OP-AMPS amplify the difference between voltages or signals applied to their two inputs.
• It's always wise to build a temporary version of a circuit before assembling it in permanent form.
• A series resistor must be used to limit current through an LED.