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Foundations of Electronics
Transcript of Foundations of Electronics
To understand how electronic systems work, you need to have an understanding of the basic concepts of voltage, resistance, current, capacitance, and inductance.
Voltage is the force that "pushes" electrons and makes them flow. Technically, it is the measure of potential difference. This measure is called voltage, which is expressed in volts.
Voltage is closely related to current, which will be explained next.
While voltage is the pressure on electrons to flow, current is the actual flow of electrons.
Current is measured in ampere, or amps for short. Since current is the flow of electrons, ampere is a measure of current that is equal to one coulomb per second.
A coulomb is a unit that measures the charge that a constant electron flow carries.
One coulomb is equal to 6.241×10^18 electrons per second.
Also, the coulomb can be expressed as:
1 C = 1 A x 1 s
Where C is equal to coulomb, A is equal to ampere, and s is equal to a second.
In short, resistance is the force that slows down the flow of electricity, or electrons.
Resistance can be compared to debris blocking the flow of water in a river. With enough resistance, or debris, the flow can slow down considerably.
Knowing the difference between current, resistance, and voltage is important. You also need to know how they relate to one another.
These relationships will be explained later in the presentation.
Conductance is the opposite of resistance; resistance is the opposing the current, where as conductance is how easily current passes through a substance.
A conductor is a device that harnesses conductive power; a device such as this in an electrical circuit is called a conductor.
Devices that are meant to create resistance are called resistors.
Resistors are made from all different kinds of materials; the specific material that a resistor is made of will depend on how much resistance is wanted in the circuit.
Conductors are made of highly conductive materials, since obviously current has to run through them.
Some of these highly conductive materials include copper and aluminum.
To define inductance, let's look at an inductor itself. An inductor is simply a coil of wire that creates its own magnetic field.
In a circuit, current flows through this coil and creates the magnetic field. However, the magnetic field cannot grow larger or smaller without the current increasing or decreasing respectively.
Inductors tend to resist changes in current.
This is because of the voltage that is created by the inductor. The voltage from the inductor flows either with or against the main current of the circuit.
The current from the inductor will flow against the main current if the circuit's current increases. This is because when the current increases, the magnetic field grows in size.
When the magnetic field grows in size, the more energy is stored in the inductor. This energy pushes against the main current, which slows down the rate of change.
The current from the inductor flows with the main current when the circuit's current decreases. This additional current from the inductor counteracts the decrease in current.
Alternating and Direct Current
With electric charge, you can either have alternating or direct current. These can be shortened to AC and DC respectively.
The difference between the two is very simple. Direct current always keeps the charges of two terminals different: positive and negative.
Alternating current, like its name, alternates periodically between the two directions.
Alternating current is generally the best option for power grid usage.
When using alternating current, transformers are used. Transformers are used to change the voltage.
Here you can see alternating and direct current illustrated. Direct current remains constant while the alternating current fluctuates.
Common Electronic Components
Electronic components are simply materials and parts used in electronic systems. This includes resistors, conductors, diodes, vacuum tubes, capacitors, and more.
There are three types of components: active, passive, and electromechanics.
Active components are those that depend on energy from the circuit to work. They also usually can insert power into the circuit.
Examples of active components are diodes, transistors, and vacuum tubes.
Diodes are components that are designed to only let current flow in one direction.
Since they limit direction, they are also used to convert alternating current to direct current. In this case, the diode is called a rectifier.
Here you can see a close up of a diode made of silicon.
Transistors are used to control the amount of electricity in a circuit. You use them to amplify or switch the amount of current.
Often, transistors are part of integrated circuits. This is because, also like diodes, transistors are made from semiconductor materials.
Semiconductors have a conductivity level between metals and insulators.
Vacuum tubes are used to control current through a sealed container (a vacuum).
Vacuum tubes are used for rectifying, amplifying, and switching electronic signals.
In fact, diodes are vacuum tubes. They operate by having two electrodes (a plate and a filament); when they are heated, the electrons inside are heated. Once an electrode is hotter than the filament, direct current begins to flow.
Vacuum tubes with three electrodes are called triodes.
This third electrode is a grid placed between the filament and the plate. When voltage is applied to the grid, it controls the current. This allows the triode to amplify the current.
Here you can see cut-away views of a diode and triode. Notice how the grid is placed in the triode.
Passive components aren't able to introduce new energy into a circuit. They also can't depend on another source of power besides what is in the circuit.
Passive components include resistors, capacitors, transformers, and inductors.
Resistors are used to create resistance in electrical circuits. This resistance can generate heat, such as those for stove tops.
Other resistors don't block all or most electron flow; this is a good thing, as some parts of the circuit need reduced flow but not heat.
Shown here is a Danotherm wire resistor.
Capacitors are used to store electrical energy in an electric field.
Capacitors operate by having two electrical conductors separated by an insulator, called the dielectric.
An electrical difference develops between the conductors, which forms an electrostatic field around the dielectric. This is where energy is stored.
Shown here is an average electrolytic capacitor.
Capacitors help to keep the level of current "even" in a circuit.
When the circuit is first connected, the capacitor starts storing electrons. Eventually, the capacitor will have the same voltage as the battery.
The storage of electrons in the capacitor is essentially a backup power source, although only for a limited time.
Transformers are used to change one voltage into another. This was mentioned previously.
Transformers are used, among other things, to change the voltage from the entire city's supply to the energy for one house.
Three power lines are sent to a house; one is the ground.
Electromechanics deals with mechanical parts being operated with electrical systems. It involves how electrical systems work with moving parts.
Some electromechanical devices include switches, terminals, and connectors.
Switches are used to break an electrical circuit. By doing this, they can either divert the current to a different conductor or stop the flow entirely.
Switches that are used in electromechanics are either toggle (on and off) or push-button switches (push on and push off).
Terminals are simply the point when a conductor comes to an end and connects to the external circuit (or circuits).
There are two terminals: negative (-) and positive(+).
Depending on how it will be used, the wire could be bare or it could have a fastener or connector attached.
Connectors go hand in hand with terminals. Connectors fall under the category of electromechanics because they use mechanical devices to connect electronic components.
Connectors can be attached permanently or temporarily; it just depends on what you need the connection for.
To the left here is a group of ring style wire connectors.
In this image, the top row of connectors is composed of ring and spade terminals. The bottom row is composed of blade connectors.
Series and Parallel Circuits
A circuit can be either a parallel or series circuit. Telling the difference between the two is very easy.
If you have, say, three lightbulbs all wired one after the other and the battery is connected at the beginning and end of the wire, then they are in a series. This is a series circuit.
Shown above is a series circuit with a battery and 3 resistors .
In series circuits, each component has the same current; the voltage varies.
To get the voltage, you simply add up the voltage of each component.
In parallel circuits, each component is directly wired to the power source, such as a battery.
To the left is an example of a parallel circuit with resistors.
In these circuits, the voltage is the same for all components because of their direct connection.
In contrast to series circuits, a parallel circuit's current varies for each component.
To find the total current, you add up the current of each component.
Connected in a series
Current is the same for
Voltage is different for
If one connection is disrupted,
the whole circuit is broken
Each component is directly
wired to the power source
Voltage is the same for each
Current is different for each component
If one connection is disrupted, the other connections still work
"Voltage." Wikipedia. N.p., n.d. Web. 18 Oct. 2013. <http://en.wikipedia.org/wiki/Voltage>.
"Electricity - Voltage and Current." Reprise. N.p., 12 Apr. 2012. Web. 18 Oct. 2013. <http://www.reprise.com/host/electricity/voltage.asp>.
"Electric current." Wikipedia. N.p., n.d. Web. 18 Oct. 2013. <http://en.wikipedia.org/wiki/Electric_current>.
"Ampere." Wikipedia. N.p., n.d. Web. 18 Oct. 2013. <http://en.wikipedia.org/wiki/Ampere>.
"Coulomb." Wikipedia. N.p., n.d. Web. 18 Oct. 2013. <http://en.wikipedia.org/wiki/Coulomb>.
"Electrical resistance and conductance." Wikipedia. N.p., n.d. Web. 18 Oct. 2013. <http://en.wikipedia.org/wiki/Electrical_resistance>.
"Electrical Resistance." The Physics Classroom. N.p., n.d. Web. 23 Oct. 2013. <http://www.physicsclassroom.com/class/circuits/u9l3b.cfm>.
"Electrical conductance." Wikipedia. N.p., n.d. Web. 23 Oct. 2013. <http://en.wikipedia.org/wiki/Electrical_conductance>.
"Resistor." Wikipedia. N.p., n.d. Web. 23 Oct. 2013. <http://en.wikipedia.org/wiki/Resistor>.
"Electrical conductor." Wikipedia. N.p., n.d. Web. 23 Oct. 2013. <http://en.wikipedia.org/wiki/Electrical_conductor>.
"How Inductors Work." How Stuff Works. N.p., n.d. Web. 23 Oct. 2013. <http://electronics.howstuffworks.com/inductor3.htm>.
"How Electricity Works." How Stuff Works. N.p., n.d. Web. 24 Oct. 2013. <http://science.howstuffworks.com/electricity8.htm>.
"Alternating current." Wikipedia. N.p., n.d. Web. 24 Oct. 2013. <http://en.wikipedia.org/wiki/Alternating_current>.
"Direct current." Wikipedia. N.p., n.d. Web. 24 Oct. 2013. <http://en.wikipedia.org/wiki/Direct_current>.
"Electronic component." Wikipedia. N.p., n.d. Web. 24 Oct. 2013. <http://en.wikipedia.org/wiki/Electronic_component>.
"Semiconductor." Wikipedia. N.p., n.d. Web. 24 Oct. 2013. <http://en.wikipedia.org/wiki/Semiconductor>.
"File:Diode-closeup.jpg." Wikipedia. N.p., n.d. Web. 24 Oct. 2013. <http://en.wikipedia.org/wiki/File:Diode-closeup.jpg>.
"Transistor." Wikipedia. N.p., n.d. Web. 24 Oct. 2013. <http://en.wikipedia.org/wiki/Transistor>.
"How Transistors Work." How Stuff Works. N.p., n.d. Web. 24 Oct. 2013. <http://electronics.howstuffworks.com/transistor1.htm>.
"Rectifier." Wikipedia. N.p., n.d. Web. 24 Oct. 2013. <http://en.wikipedia.org/wiki/Rectifier>.
"Vacuum tube." Wikipedia. N.p., n.d. Web. 24 Oct. 2013. <http://en.wikipedia.org/wiki/Vacuum_tube>.
"File:Diode-english-text.svg." Wikipedia. N.p., n.d. Web. 24 Oct. 2013. <http://en.wikipedia.org/wiki/File:Diode-english-text.svg>.
"File:Triode-english-text.svg." Wikipedia. N.p., n.d. Web. 24 Oct. 2013. <http://en.wikipedia.org/wiki/File:Triode-english-text.svg>.
"Resistor." How Stuff Works. N.p., n.d. Web. 24 Oct. 2013. <http://science.howstuffworks.com/resistor-info.htm>.
Fairfield, Jessamyn. "How Resistors and Capacitors Work." Let's Talk About Science. N.p., n.d. Web. 24 Oct. 2013. <http://letstalkaboutscience.wordpress.com/2012/05/28/how-resistors-and-capacitors-work/>.
"Capacitor." Wikipedia. N.p., n.d. Web. 24 Oct. 2013. <http://en.wikipedia.org/wiki/Capacitor>.
"File:Danotherm_HS50_power_resistor.jpg." Wikipedia. N.p., n.d. Web. 24 Oct. 2013. <http://en.wikipedia.org/wiki/File:Danotherm_HS50_power_resistor.jpg>.
"File:Condensador_electrolitico_150_microF_400V.jpg." Wikipedia. N.p., n.d. Web. 24 Oct. 2013. <http://en.wikipedia.org/wiki/File:Condensador_electrolitico_150_microF_400V.jpg>.
"How Capacitors Work." How Stuff Works. N.p., n.d. Web. 24 Oct. 2013. <http://electronics.howstuffworks.com/capacitor.htm>.
"Transformer." Wikipedia. N.p., n.d. Web. 24 Oct. 2013. <http://en.wikipedia.org/wiki/Transformer>.
"How Does a Transformer Work." Energy Quest. N.p., n.d. Web. 24 Oct. 2013. <http://www.energyquest.ca.gov/how_it_works/transformer.html>.
"Electromechanics." Wikipedia. N.p., n.d. Web. 24 Oct. 2013. <http://en.wikipedia.org/wiki/Electromechanics>.
"What is Electromechanics." Wisegeek. N.p., n.d. Web. 24 Oct. 2013. <http://www.wisegeek.com/what-is-electromechanics.htm>.
"Solenoid." Wikipedia. N.p., n.d. Web. 24 Oct. 2013. <http://en.wikipedia.org/wiki/Solenoid>.
"Switch." Wikipedia. N.p., n.d. Web. 24 Oct. 2013. <http://en.wikipedia.org/wiki/Switch>.
"Terminal (electronics)." Wikipedia. N.p., n.d. Web. 24 Oct. 2013. <http://en.wikipedia.org/wiki/Terminal_(electronics)>.
"Electrical connector." Wikipedia. N.p., n.d. Web. 24 Oct. 2013. <http://en.wikipedia.org/wiki/Electrical_connector>.
"File:Ring_wire_end_connector.jpg." Wikipedia. N.p., n.d. Web. 24 Oct. 2013. <http://en.wikipedia.org/wiki/File:Ring_wire_end_connector.jpg>.
"File:Kabelschuh_verschiedene_commons.jpg." Wikipedia. N.p., n.d. Web. 24 Oct. 2013. <http://en.wikipedia.org/wiki/File:Kabelschuh_verschiedene_commons.jpg>.
"Series and parallel circuits." Wikipedia. N.p., n.d. Web. 25 Oct. 2013. <http://en.wikipedia.org/wiki/Series_and_parallel_circuits>.
"File:Series_circuit.svg." Wikipedia. N.p., n.d. Web. 25 Oct. 2013. <http://en.wikipedia.org/wiki/File:Series_circuit.svg>.
"File:Resistors_in_parallel.svg." Wikipedia. N.p., n.d. Web. 25 Oct. 2013. <http://en.wikipedia.org/wiki/File:Resistors_in_parallel.svg>.
Laws of Electronics
There are three laws that are important to know for working with electronics. They are Ohm's Law and Kirchhoff's Laws.
Remember earlier when I mentioned that the way current, voltage, and resistance interact is important? This is why.
Ohm's law is really simple. It says that the current of a conductor in a circuit is found by dividing the voltage by the resistance.
You can use this relationship to figure out what voltage and resistance are equal to.
By doing simple math, you see that voltage is equal to the current multiplied by the resistance. The resistance is the voltage divided by the amps (current).
Let's use a simple example of a circuit.
In this circuit, you have a 12 volt battery and a lightbulb with 6 ohms of resistance. You need to find the current.
You know that current is the voltage divided by the resistance, so we do this:
I = 12/6
So there's 2 amps of current in this circuit.
Another useful tool is this:
You cross out the value that you don't know and you're left with an equation to find the missing value.
If you didn't know the voltage, you cross out the V and you're left with I and R, so it's current times resistance.
Or, if you didn't know current, you're left with voltage divided by resistance.
Kirchhoff's laws deal with current and voltage in circuits. There are two laws, just called Kirchhoff's First Law and Kirchhoff's Second Law.
Kirchhoff's First Law is sometimes called Kirchoff's Point or Joint rule. It says that for any junction in a circuit, the sum of the current is zero.
A little more complicated way of explaining it is this:
The current that flows into a junction is equal to the current flowing out of that junction; this should equal zero.
Below is the equation for his first law.
N is equal to the number of branches flowing to and from the junction.
Kirchhoff's second law is also called Kirchhoff's voltage law or the loop rule.
The second rule says that the voltage drop in a circuit is the same as the rate that the rate of change in the loop flux.
For example, if the magnetic loop is large, the voltage drop would be large, and if it's small, then the voltage drop will be small.
Above is the formula for Kirchhoff's voltage law.
Here, N is the number of voltages being measured in a circuit.
Analog and Digital Signals
Analog and Digital signals are common in this: they both record and transmit electrical signals.
Analog is able to transmit signals continuously, in a sort of constant wave formation.
Digital signals transmit signals, but they are interrupted. They don't make a smooth wave like the analog signals.
You can see a visualization of analog and digital signals here.
Another thing to note about digital signals is that they operate in binary. Positive values are a one while the rest are zeros.
Digital signals are easier to store than analog signals since it is a string of ones and zeros.
Digital signals also contain less noise than analog signals since they are not constant.
"Ohm's law." Wikipedia. N.p., n.d. Web. 28 Oct. 2013. <http://en.wikipedia.org/wiki/Ohm's_law>.
"Kirchhoff's circuit laws." Wikipedia. N.p., n.d. Web. 28 Oct. 2013. <http://en.wikipedia.org/wiki/Kirchhoff's_circuit_laws>.
"How voltage, current, and resistance relate." All About Circuits. N.p., n.d. Web. 28 Oct. 2013. <http://www.allaboutcircuits.com/vol_1/chpt_2/1.html>.
"Does digital sound better than analog?." How Stuff Works. N.p., n.d. Web. 28 Oct. 2013. <http://electronics.howstuffworks.com/digital-versus-analog1.htm>.
"What Is the Difference between Analog and Digital Signals?." Ask. N.p., n.d. Web. 28 Oct. 2013. <http://www.ask.com/question/what-is-the-difference-between-analog-and-digital-signals>.
"Analog signal." Wikipedia. N.p., n.d. Web. 28 Oct. 2013. <http://en.wikipedia.org/wiki/Analog_signal>.
"Digital signal." Wikipedia. N.p., n.d. Web. 28 Oct. 2013. <http://en.wikipedia.org/wiki/Digital_signal>.
"Analog & Digital Signals." Through the Wires. N.p., n.d. Web. 28 Oct. 2013. <http://library.thinkquest.org/27887/gather/fundamentals/analog_and_digital.shtml>.
Translating Logical Expressions
Translating logical expressions is similar to using binary code or Boolean logic. Data is represented by values that correspond to real life things.
In terms of electronics, this could also be applied to formulas and what the values for current, voltage, and resistance are.
So if you said that a circuit has a voltage of 12 with a resistor that produces 5 Ohms, you could illustrate it with this:
This image translated the logical expression into a symbolic representation.
Breadboards and Soldering
Instead of describing how breadboards work and what soldering is, I'll be explaining it in a video.
"Breadboard." Wikipedia. N.p., n.d. Web. 8 Nov. 2013. <http://en.wikipedia.org/wiki/Breadboard>.
"Soldering." Wikipedia. N.p., n.d. Web. 8 Nov. 2013. <http://en.wikipedia.org/wiki/Soldering>.
"File:400 points breadboard.jpg." Wikipedia. N.p., n.d. Web. 8 Nov. 2013. <http://en.wikipedia.org/wiki/File:400_points_breadboard.jpg>.
"File:Breadboard complex.jpg." Wikipedia. N.p., n.d. Web. 8 Nov. 2013. <http://en.wikipedia.org/wiki/File:Breadboard_complex.jpg>.
"Breadboard How To." Instructables. N.p., n.d. Web. 8 Nov. 2013. <http://www.instructables.com/id/Breadboard-How-To/>.
"Jump wire." Wikipedia. N.p., n.d. Web. 8 Nov. 2013. <http://en.wikipedia.org/wiki/Jump_wire>.
"File:Breadboard.JPG." Wikipedia. N.p., n.d. Web. 8 Nov. 2013. <http://en.wikipedia.org/wiki/File:Breadboard.JPG>.
"File:Breadboard with 4008B.jpg." Wikipedia. N.p., n.d. Web. 8 Nov. 2013. <http://en.wikipedia.org/wiki/File:Breadboard_with_4008B.jpg>.
"File:Breadboard.svg." Wikipedia. N.p., n.d. Web. 8 Nov. 2013. <http://en.wikipedia.org/wiki/File:Breadboard.svg>.
"File:Desoldering.jpg." Wikipedia. N.p., n.d. Web. 8 Nov. 2013. <http://en.wikipedia.org/wiki/File:Desoldering.jpg>.
"File:A_few_Jumper_Wires.jpg." Wikipedia. N.p., n.d. Web. 8 Nov. 2013. <http://en.wikipedia.org/wiki/File:A_few_Jumper_Wires.jpg>.
"Flux (metallurgy)." Wikipedia. N.p., n.d. Web. 8 Nov. 2013. <http://en.wikipedia.org/wiki/Flux_(metallurgy)>.
"File:272-06201_Shop.jpg." Wikipedia. N.p., n.d. Web. 8 Nov. 2013. <http://en.wikipedia.org/wiki/File:272-06201_Shop.jpg>.
"Oxidation." Wikipedia. N.p., n.d. Web. 8 Nov. 2013. <http://en.wikipedia.org/wiki/Oxidation>.
"File:Soldering-step2c.jpg." Wikipedia. N.p., n.d. Web. 8 Nov. 2013. <http://en.wikipedia.org/wiki/File:Soldering-step2c.jpg>.
Electronic Test Equipment
When working with circuits (both analog and digital), you need to familiarize yourself with some meters and tools.
Similar to its name, the voltmeter measures the voltage in a circuit.
In an analog voltmeter, the difference in the two points is measured by using a pointer that moves across a scale, which indicates the voltage.
In a digital voltmeter, an analog-to-digital converter is used.
Here you can see an analog voltmeter.
An Ohmmeter, again, is similar to its function; it measures the resistance in a circuit (Ohms).
Often, ohmmeters are part of multimeters, which measure voltage, resistance, and current.
Ohmmeters use a small electrical current in order to read the resistance. You would also use an ohmmeter to check if the circuit is continuous.
If the circuit reads as "open" and not continuous, then it has a break.
If you test a circuit with your ohmmeter and it comes back with an infinity sign or "OL" then the circuit is open.
Here you can see an ohmmeter reading "OL" or "open line."
Ammeters are used to measure the current in a circuit (which is measured in amperes).
In an analog ammeter, there is a coil of wire that the current is run through. This current makes the wire part of a magnetic field.
This field causes the coil to move, which indicates the amount of ampere on a scale.
Here you can see an analog ammeter, which is also called a moving iron ammeter or moving coil ammeter.
Digital ammeters use digital-to-analog technology to measure current.
These ammeters are similar to voltmeters; they produce a voltage that is equal to the voltage in the circuit. From this, the digital display is able to show the amount of current in the circuit.
To the left is a digital Zero-Center ammeter from 2008.
Multimeters are used to measure voltage, current, and resistance in either an analog or digital circuit.
In an analog multimeter, there are different scales for all of the measurements that can be taken. A pointer moves across the scale to tell what the number of the measurement is.
Here you can see the face of an analog multimeter.
A digital multimeter has a display screen that shows the values in numerals. Depending on the multimeter, it may also display the value being measured.
Multimeters can also be called VOM meters (Volt-Ohm) or DMM meters (Digital Multimeter).
Here you can see a digital multimeter. Notice how you can change the value being measured with the dial.
"Electronic test equipment." Wikipedia. N.p., n.d. Web. 11 Nov. 2013. <http://en.wikipedia.org/wiki/Electronic_test_equipment>.
"Voltmeter." Wikipedia. N.p., n.d. Web. 11 Nov. 2013. <http://en.wikipedia.org/wiki/Voltmeter>.
"File:Voltmeter hg.jpg." Wikipedia. N.p., n.d. Web. 11 Nov. 2013. <http://en.wikipedia.org/wiki/File:Voltmeter_hg.jpg>.
"Ohmmeter." Wikipedia. N.p., n.d. Web. 11 Nov. 2013. <http://en.wikipedia.org/wiki/Ohmmeter>.
"Using an Ohm Meter." Tiger Stop. N.p., n.d. Web. 11 Nov. 2013. <http://www.tigerstop.com/tigertamer/Using_an_Ohm_Meter.htm>.
"Ohm-meter-300w.jpg." Tiger Stop. N.p., n.d. Web. 11 Nov. 2013. <http://www.tigerstop.com/tigertamer/ohm-meter-300w.jpg>.
"Ammeter." Wikipedia. N.p., n.d. Web. 11 Nov. 2013. <http://en.wikipedia.org/wiki/Ammeter>.
"File:Amperemeter hg.jpg." Wikipedia. N.p., n.d. Web. 11 Nov. 2013. <http://en.wikipedia.org/wiki/File:Amperemeter_hg.jpg>.
"File:Zero-Center Ammeter.JPG." Wikipedia. N.p., n.d. Web. 11 Nov. 2013. <http://en.wikipedia.org/wiki/File:Zero-Center_Ammeter.JPG>.
"File:Digital Multimeter Aka.jpg." Wikipedia. N.p., n.d. Web. 11 Nov. 2013. <http://en.wikipedia.org/wiki/File:Digital_Multimeter_Aka.jpg>.
"File:Multimeter-4269.jpg." Wikipedia. N.p., n.d. Web. 11 Nov. 2013. <http://en.wikipedia.org/wiki/File:Multimeter-4269.jpg>.
"Multimeter." Wikipedia. N.p., n.d. Web. 11 Nov. 2013. <http://en.wikipedia.org/wiki/Multimeter>.