Basic Electronic Overview



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Electron theory and atoms

All matter is comprised of molecules, which in turn are comprised of atoms, which are again comprised of protons, neutrons and electrons. A molecule is the smallest part of matter which can exist by itself and contains one or more atoms. (More: Electron theory and atoms)


In the topic current we learnt that certain materials such as copper have many free electrons. Other materials have fewer free electrons and substances such as glass have practically no free electron movement therefore making good insulators. Between the extremes of good conductors such as silver, copper and good insulators such as glass and rubber lay other conductors of reduced conducting ability, they "resist" the flow of electrons hence the term resistance.. ( More: Resistance )

Ohms Law

Ohms law, named after Mr. Ohm, defines the relationship between power, voltage, current and resistance. These are the very basic electrical units we work with. The principles apply to a.c., d.c. or r.f. (radio frequency). ( More: Ohms Law )


A flow of electrons forced into motion by voltage is known as current. The atoms in good conductors such as copper wire have one or more free electrons of the outer ring constantly flying off. Electrons from other nearby atoms fill in the holes. There are billions of electrons moving aimlessly in all directions, all the time in conductors. (More: Current )


Voltage should be more correctly called "potential difference". Voltage is actually the electron moving force in electricity (emf) and the potential difference is responsible for the pushing and pulling of electrons or electric current through a circuit. (More: Voltage)


In the topic current we learnt of the unit of measuring electrical quantity or charge was a coulomb. Now a capacitor (formerly condenser) has the ability to hold a charge of electrons. The number of electrons it can hold under a given electrical pressure (voltage) is called its capacitance or capacity. Two metallic plates separated by a non-conducting substance between them make a simple capacitor. Here is the symbol of a capacitor in a pretty basic circuit charged by a battery. (More:Capacitance )


The property of inductance might be described as "when any piece of wire is wound into a coil form it forms an inductance which is the property of opposing any change in current". Alternatively it could be said "inductance is the property of a circuit by which energy is stored in the form of an electromagnetic field. (More:Inductance)


Reactance is the property of resisting or impeding the flow of ac current or ac voltage in inductors and capacitors. Note particularly we speak of alternating current only ac, which expression includes audio af and radio frequencies rf. NOT direct current dc.This leads to inductive reactance and capacitive reactance. (More:Reactance)


Resonance occurs when the reactance of an inductor balances the reactance of a capacitor at some given frequency. In such a resonant circuit where it is in series resonance, the current will be maximum and offering minimum impedance. In parallel resonant circuits the opposite is true. (More:Resonance)


Impedance is one of the most confusing aspects of electronics - I will de-mystify impedance by taking an extremely casual approach. I have known electronic enthusiasts who still couldn't even mentally visualise the concept of impedance even after 25 years. (More:Impedance)


Diodes are semiconductor devices which might be described as passing current in one direction only. The latter part of that statement applies equally to vacuum tube diodes. Diodes however are far more versatile devices than that. They are extremely versatile in fact. (More:Diodes)


Generally transistors fall into the category of bipolar transistor, either the more common NPN transistors or the less common PNP transistor types. There is a further type known as a FET transistor which is an inherently high input impedance transistor with behaviour somewhat comparable to valves. Modern FET's include some very rugged transistor devices. (More:Transistors)


The name transformers is derived from the fact that when two coils are placed in close inductive proximity to one another the lines of force from one cut across the the turns of the other inducing an ac current, energy is transformed from one winding to another and this is called transformer action. (More:Transformers)

Radio Terminology

start in the fascinating and wonderful world of electronics by learning the primary basics - radio terminology. You need a clear understanding of all radio and electronics terms.

Radio-Terminology A-L

Radio-Terminology M-Z


Among the foremost of reasons an electronic project frequently fails to work properly is due to "poor" soldering practices. This is usually caused by "dry joints" when soldering. Here I discuss the correct procedures for soldering electronic projects.



How important is soldering?

Among the foremost of reasons an electronic project frequently fails to work properly is due to "poor" soldering practices. This is usually caused by "dry joints" when soldering. Here I discuss the correct procedures for soldering electronic projects.

Dry joints when soldering

At first glance many solder joints appear to be quite "O.K." but on closer examination many are in fact defective. The insidious problem with dry joints in soldering is that the circuit frequently performs alright for a period of time, even years before failure.

This problem even occurs with manufactured equipment. Ask any TV / Video repair technician who has torn a lot of hair out over an elusive fault ultimately traced back to a dry joint.

Good soldering practices for your electronic project

The cause of dry joints in soldering is mostly the improper application of heat. Both the component leg and the PCB need to be both heated simultaneously to the correct temperature to allow the solder to flow freely between BOTH surfaces. Obviously this requires practice and most newcomers inevitably get it wrong.

Improper heating while soldering and its consequences can be seen below.

correct soldering procedures to avoid dry joints

Figure 1 - correct soldering procedures to avoid dry joints

Here in figure 1 entitled "correct soldering procedures to avoid dry joints" we have three examples of soldering depicted. The first example indicates the component lead was heated while the PCB wasn't heated. As a consequence the solder only flowed onto the component lead.

In the second example of soldering in figure 1 we find the PCB was correctly heated while little or inadequate heat was applied to the component lead. This is the most treachorous example because although I have made it very obvious in the diagram, in practice it is not always particularly obvious. Often this type of dry joint "just" allows the solder to "touch" the component lead while not actually being "soldered" to the lead. Of course it might work for a period of time depending upon environmental conditions of heat and cold.

In the final example of "correct soldering procedures to avoid dry joints" I have depicted the solder bridging both the PCB and the component lead. In this case the PCB and the component lead were both heated "simultaneously" AND the solder was applied to either the component lead or the PCB to "flow" freely from one to the other to provide a good "electrical" joint. Such a joint is always "bright and shiny", dull looking joints are often suspect.

You never apply the solder to the soldering iron "tip". Solder is always applied to the "job", never the soldering iron. Allow the solder to "set" and cool before proceeding to the next joint.

Other cases of soldering

We have discussed soldering components to a PCB yet this is not the only case of soldering. Often we need to connect wires to switches and other components. A common misconception is that soldering is designed to provide a good mechanical joint. - It isn't!

Any connection should have it's own mechanical strength perhaps by twisting wires together or twisting the wire around a binding post or through a hole provided for the purpose. The solder is only intended for a good "electrical" connection. Never provide a connection which can't stand mechanically on it's own merits.

What's soldering flux?

Modern quality electronics solders contain a "flux" resin within the solder. This flux is designed to flow over the job and prevent contact with the atmosphere. Metals, particularly copper when heated tend to "oxidise" and prevent the alloying or good electrical bond between the copper and the solder.

Good solder containing the resin will have resin flowing over the leads and prevent this oxidisation process and as the solder flows the resin is displaced allowing the solder to form an "atomic" bonding with the items being soldered together. A good resin helps to keep the surfaces clean.

Rules for good soldering

Of course some of these rules might seem very obvious but are worth repeating.

-Use a reasonable quality iron of the correct wattage for the job.

-Only use "electronic" resin cored solder of fine gauge.

-Make sure all surfaces to be soldered are "bright, shiny" and thoroughly clean

-If a mechanical joint, make sure it can "stand alone" before soldering.

-Make sure the solder tip is clean, shiny and properly "wetted".

-Remember the soldering iron tip is only to heat up the surfaces to be soldered.

-Apply the resin cored solder to the heated "job", not to the soldering iron tip.

-Remember to visually inspect ALL of your soldered joints, preferably with magnifying glasses.

-Consider using your multimeter to provide an "electrical continuity" check between various parts of the circuit.









The inside of a typical household wall switch has a strip of metal (B), making contact with point 'A', completing the circuit and thereby conducting electricity to the light. This would obviously be the 'ON' position. When the insulated lever is moved down to the 'OFF' position, it pushes the metal strip away from point 'A', breaking the circuit and turning the light 'OFF'.
This type of switch (having a lever which "flips" it on and off) is called a toggle switch.

Because of being well-insulated and mounted in a box, household switches are a safe way for turning electrical devices on and off.


There are many different types of switches: toggle, rotary, pushbutton, "rocker", "pull-chain", slide, magnetic, mercury, timer, voice-activated, "touch-sensitive", and many others. Heck, even the Clapper™ is another type of switch !

          The "knife switch" (rarely seen nowadays) is the type that most easily demonstrates the functioning of a switch. Old sci-fi movies ("Frankenstein (1931)" or "Young Frankenstein (1974)" , for example), made extensive use of these switches in the laboratory scenes.

Today, use of knife switches has been confined to 1) heavy-duty industrial applications and 2) demonstration purposes - science projects for example. The knife switch has a metal lever, insulated at the 'free end' that comes into contact with a metal 'slot'. Since the electrical connections are exposed, knife switches are never seen in household wiring.

Pushbutton switches are usually "momentary on". That is to say the connection is made only when you press the button.(doorbell switches)

A practical use of the momentary off switch is the "mute button" on your telephone. If a momentary on switch were used, it would be very annoying to press the button constantly as you talked and released it only for muting. This shows how each type of switch has its specific applications.

          Notice in the above diagram that a relay uses an electromagnet. This is a device consisting of a coil of wire wrapped around an iron core. When electricity is applied to the coil of wire it becomes magnetic, hence the term electromagnet. The A B and C terminals are an SPDT switch controlled by the electromagnet.   When electricity is applied to V1 and V2, the electromagnet acts upon the SPDT switch so that the B and C terminals are connected. When the electricity is disconnected, then the A and C terminals are connected. It is important to note that the electromagnet is magnetically linked to the switch but the two are NOT linked electrically.

          There is another type of relay called a solenoid that basically works on the same principle. The solenoid electromagnet consists of wire wrapped around a tube containing an iron cylinder called a "plunger". When electricity is supplied to the wire coil, the "plunger" moves through the tube and activates a switch.

          At this point you might be wondering about the purpose of all this. Why switch an electromagnet just so it can control another switch? Why not just use one regular switch? One important application is illustrated in the diagram below.

NOTE: the symbol indicates a ground connection. Since a great percentage of an automobile consists of metal, using the automobile itself as one "side" of a circuit saves a tremendous amount of wire.