library: electronics - basic concepts
 
Note: The following is the first in a series of articles covering basic electronic system concepts. It appeared in a variety of industry trade publications and has been updated from time to time.
 
Author: Paul M. Allen

Electronic products have come to dominate our daily lives but most of us have no idea what electronics is or how the electronic products that have changed the way we live work.

If you're in the least bit curious, this article is for you. 

The bottom line is that the subject isn't really all that complicated. All that's needed to gain a general understanding of the subject is to master a few basic principles and learn a handful of key words.

Example: Your wife blows a fuse when she turns on her hair dryer. Why did that happen?

By the time you get to the end of the article, you'll be able to explain to her in technical terms that the circuit carrying power to the plug in the wall was drawing too many amps. She probably won't have any idea what an amp is but she might be impressed that you do.

 
the basics
 

The thing that makes electronics hard to get our arms around is that we find ourselves dealing with things we can't see and obscure concepts that nobody ever took the time to explain to us in terms we could understand.

As with other things, understanding why the lights come on when you flip the switch or how your computer does whatever it does begins with learning the basics and then building on what you know.

Electricity is a form of energy made up of sub-microscopic particles called electrons. When we slip the word electronics into a conversation what we're talking about is electricity

The use of two terms to describe the same thing is due to the fact that electricity was discovered and put to work long before anyone other than a few physicists knew anything about the electron.

Over the years, a practical difference between the two terms has emerged. Electrical Systems are generally thought of as those that use relatively large amounts of electrical power while Electronic Systems use small amounts of power. In that context, we have electric lights and the multitude of low power electronic digital devices that have come to dominate our lives.

 
electrons
 

Electrons are negatively charged particles that orbit around the nucleus of an atom in the same way that the planets in our solar system orbit around the Sun.

In certain materials such as copper, the outermost electrons in the atoms that make up the copper can be broken free with relative ease. When that happens they become Free Electrons.

The two characteristics that make Free Electrons useful are that (1) they repel other electrons and (2) they are attracted to atoms that have a shortage of electrons. As a result, unless they are restrained in some manner, they are in constant motion - moving away from other electrons and towards atoms that have an electron deficiency.

If you take a piece of copper wire, for example, and create a surplus of Free Electrons at one end and a deficiency of electrons at the other end, the surplus of electrons will move at the speed of light to the end where the shortage exists. That directional flow of electrons is electric current. If you put a switch somewhere in the wire, the switch will either provide an uninterrupted path between the two ends of the wire or create a break that prevents the electrons from getting from point A to point B.

When electrons begin to flow, energy is being expended that can be harnessed to perform specific tasks.

 
creating electricity
 

The flow of electrons doesn't just happen. Something has to occur to break electrons free from their atoms. Typically, the process takes place when electrons are broken loose by moving a magnet past a copper wire. A couple examples are a hydroelectric power plant and the alternator in your car. Batteries  are the "storage tanks" that warehouse the energy for later use.

 
volts, amps, ohms, and watts
 

Electrical system activity is measured in volts, amps, ohms, and watts.

Voltage is the measure of the potential difference between the number of surplus electrons at one point (the - side of the circuit) and the electron deficiency at the other end (the + side of the circuit). That difference is important because it represents the amount of force that will be generated if the electrons move between the two points.

Voltage is referred to as electromotive force - EMF.

Frequently, voltage is compared to pressure since it is the force that makes the electrons flow.

Amperage is the measure of the rate of flow. It is the volume of electrons passing though a given point in a circuit.

Electricians live by the rule that, "It's the amps (the volume of electrons) that kill, not the volts."

The stun guns used in law enforcement, for instance, put out high voltage but generate only a few thousandths of an amp to create a very unpleasant - but not fatal - experience for the person on the receiving end of the shock.

One ampere is a current flow of one columb per second. A columb is a cubic centimeter of electrons - approximately 6.25 million, million, million if you were to have the time and inclination to count them.

When electrons flow, there is always some resistance. That resistance is measures in Ohms.

One Ohm is the amount of resistance that will allow one amp of current to flow if one volt is present. Remember, voltage is "pressure" and amperage is "volume".

Ohm's Law is one of the basic tools of electronics. It expresses the relationship between voltage, the current flow in amps, and the resistance in ohms. It is:

AMPS = VOLTS / OHMS

or

VOLTS = AMPS * OHMS

or

OHMS = VOLTS / AMPS

The point is that if you know two out of the three values, you can figure out the missing value without directly measuring it.

The Watt is the measure of electrical power or the rate at which work is being done. Examples of work would include heating the wire that creates light inside a light bulb or turning an electric motor.

One watt is equal to one amp of current flowing in a circuit at one volt.  

WATTS = VOLTS * AMPS

To visualize the concept, consider the example of a typical 60 watt light bulb in your home.

WATTS(60) = VOLTS(120) * AMPS(0.5)

The illustration demonstrates that under ideal circumstances, the kind of 120 volt circuit rated at 15 amps you would find in most homes would carry enough power to light thirty of the 60 watt bulbs used in our example. Adding more bulbs would cause the fuse to blow because the circuit was drawing too many amps.

Getting back to the subject of hair dryers; they consume a lot of power. Hair dryers include both a power consuming heating element and a power consuming fan motor. A typical 1800 watt hair dryer can draw the same amount of power as thirty 60 watt light bulbs, placing a substantial load on the circuit and creating the possibility that that the circuit will be overloaded if there are other power consuming devices in use on the circuit when the hair dryer is turned on.

So, why don't fuses in 15 amp circuits blow every time a hair drier is turned on? The answer is that devices are rated on the basis of the maximum amount of power they might use, not the lower amount they may actually use at any given moment. Typically, the maximum is approached when the device is started, after which the power usage drops to a lower level (which also explains why electrical device failures almost always occur the instant the device is turned on, not after it has been running for a while).

 

putting it all together

 

The voltage available in an electrical system is determined by the ability of the power source to create a difference between the surplus of electrons at one point (the - terminal) and the shortage that exists at another point (the + terminal).

In the case of your home, the electric company typically delivers 120 volts to your fuse box. Appliances that require 220 volts, such as a stove or clothes dryer, get their power by drawing it from two 120 volt circuits. 

Your car uses 12 volts supplied by the battery which is kept charged by the alternator. 

To move between the point where the power is generated and used, the electrons that represent the energy typically travel along a copper wire. The rate at which they flow is measured in AMPS. The number of amps a circuit draws is determined by how much power any devices inserted into the circuit consume.

There is always some resistance which is measured in OHMS.

In the final analysis, circuits that require lots of power need big wires to carry that power. As the power requirement drops, the wires get smaller.

In the case of computer chips and other electronic components, the amount of power used is so small that the "wires" can become microscopic in size. Actually, they aren't really wires at all but are tracings of conductors placed on circuit boards or in computer chips.  

 

the tools of the trade

 

Carpenters use hammers and saws and drills and tape measures. People who work with electrical and electronic systems use their own specialized tools.

The most important tools for those dealing with electrical and electronic systems are the ones they use to measure the electrical power in the circuit - something they can't see and quickly learn that they probably shouldn't touch.

An Ammeter is used to measure the flow of current. To do its job, it must be inserted into the circuit so that all the power passing though the circuit will pass through the ammeter.

A Voltmeter is a highly sensitive ammeter connected in series with a device called a Multiplier Resistor that limits the current flow.

An Ohmmeter measures the resistance in the circuit.

Typically, the devices are combined into the kind of Digital Multi-meter carried by anyone who works with electrical or electronic systems.

While costly Digital Multi-meters are the tools of choice for professionals, an inexpensive Analog Volt/Ohm Meter or low cost Digital Multi-meter is a worthwhile addition to almost anyone's toolbox.

Needless to say, the risks involved make it unwise for anyone other than a professional to attempt to work with systems that carry a lot of power.

Amateurs should restrict themselves to using their Volt/Ohm Meters to measure the power in low voltage/low amperage circuits.

Automobiles, for instance, use 12 volt systems. If the power in the battery drops below 9 volts, the vehicle won't start. A simple test with a volt/ohm meter tells you all you need to know.

 

electronic units of measurement

 

Electrical systems carry lots of power. Electronic systems don't carry much at all. The amounts of power are so small that different units of measurement are required - those that represent thousandths or even millionths of volts amps and ohms.

Just when things begin to make sense, somebody decides that it really shouldn't be that easy.

In this case, measurements that represent thousandths use the prefix "milli" which we would logically expect to represent millionths and the prefix "micro" which we tend to think means nothing more than really small is used to represent millionths.

Thus, we have:

Millivolts - thousandths of a volt. A millivolt is .001 volt. Symbol: mV.

Milliamps - thousandths of an amp. A milliamp is .001 amp. Symbol: mA.

Milliohms - thousandths of a volt. A millivolt is .001 volt. Symbol: mV.

Microvolts - milllionths of a volt. A microvolt is .000001 volt. Symbol: uV.

Microamps millionths of an amp. A microamp is .000001 volt. Symbol: uA.

Micro-ohms millionths of an ohm. A micro-ohm is .000001 ohm.



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