Electronics Basics

RESISTORS

Resistors come in all types of packages but they all do the something, which is to limit current. Resistors are pretty easy to keep track of because they are color-coded.

Below are some common ways resistors are depicted in schematics. The most common way is with the use of R1. In schematics you will usually find the value of the resistor using color code. R3 and R4 are variable resistors. These are resistors, which you can change the resistance of. Variable resistors are called potentiometer. They are used to adjust the volume of radios, brightness of a lamp or adjust the sensitivity of a sensor. These resistors are not color coded, but you’ll most often find a stamped labeled on the bottom or inner ring giving the value of pots as they are called. Another version of the variable resistor is the trimmer. These are potentiometers with a plastic thumbwheel or slot for a screwdriver and are designed for occasional adjustments. R5 is a photo resistor, which is sensitive to light and gives a higher or lower resistance value depending on the level of light.

Fixed Resistor

Variable Resistor or Potentiometer

CAPACITORS

Capacitors have 3 primary functions:

1. To store a charge, much like a battery. These capacitors are normally electrolytic and are used in situations like power supplies where a fluctuating DC voltage needs to be smoothed, or, have the ripple taken out.

2. A capacitor is used to block DC while allowing AC to pass through such as in an audio amplifier where we are passing the audio signal through from one stage to the next.

3. To counteract inductive reactance in order to create a “tuned circuit”.

4. A cap can also be used as a spike filtering, which is slightly different than smoothing an AC signal. The term for this purpose is “bypass cap” in case anyone out there was wondering about that one.

When power gets to them they hold a charge right away, but will eventually discharge if left alone or you can discharge a capacitor by hitting both of it’s leads together or connect a resistor between both leads. Capacitors have different levels, which are specified in farads. Below are common schematics symbols for capacitors and common farad ratings.

An important thing to take notice of is that capacitors DO NOT add in series like resistors, just the opposite,
two 1mfd capacitors in series equal 0.5 mfd.

SWITCHES

I know, you are saying I know what a switch is. Well we are going to learn about them anyway. First let’s look at S1, this is a Normally Open push button switch. NO is short for Normally Open. This would be a good simple way to add a sensor for a robot when it hits a wall. If this switch hit a wall it would close and complete the circuit and current would travel though it. S2 is a NC or Normally Closed switch. When a NC switch is hit is opens the circuit and so no current runs though it while it is depressed.

DIODES

There are different types of diodes. The most common in small electronics is the signal diode shown in fig.2 and can be used to transform low current from AC to DC, multiply voltage, perform logic and absorb voltage spikes created by other devices. You also have your zener diodes that can function like a voltage sensitive switch. You also have your LED’s, which stand for Light Emitting Diodes, which we will discuss later. And you have your photodiode, which detects light, this also to be addressed later. Circuit schematics will always give you the name of the diode used, it will be something like 1N4003 or 1N914…this is how you will look them up to order or buy them at a local electronics store.

An important note on all forms of diodes is that they are not like resistors; they have positive and negative ends. Current will flow when a diode’s Anode end is more positive than it’s Cathode end.

LED’s

LED stands for Light Emitting Diode. LED’s convert an electrical current directly into light. The light emitted by an LED is directly proportional to current through the LED. This means LED’s are ideal for transmission of information. However, LED’s need direct line of sight and they usually have a short range of light emission. Because LED’s are current dependent they need to be protected from excessive current with a resistor. For most robotic applications with power sources of around 9 volts I find that a 1K resistor will always to the trick. A normal schematics symbol for a LED is pictured below along with a drawing of what an actual LED looks like. You’ll notice one lead is longer than the other, in most cases a longer lead indicates that it is the positive lead.

OPTICS

A Photo-Resistor is acts like a variable resistor because it changes resistance as the light level changes. They have no positive or negative end and there resistance is very high (up to millions of ohms) when no light is present. These are great for simple robotics eye to find the darkest or brightest point in a room or detect the difference between day and night. You’ll find photo resistor in many common security sensor and toys, including the Furby.

Now what is the schematics symbol that looks like a box with a LED and phototransistor inside? It is an “Opto isolator” which means simply optical isolator. It really is not much more than a box with a Light Emitting Diode and a phototransistor inside. This would not be used as a sensor. It as used as a switch. Say you have a high-powered motor you want to control with your computer. You would use an opto isolator in-between your computer and motor (along with other proper control circuitry) so that you computer can control your motor with out being directly linked to the motor incase something should go wrong the motor end, nothing will happen to your computer because it is “isolated” via the opto isolator!

TRANSISTORS

Transistors are semiconductor devices with three leads. For those that don’t know “leads” simply refer to the pins or wires coming from a device or component. A very small current or voltage at one lead can control a much larger current flowing through the other two leads. This type of action turns a transistor into a mechanical switch. That’s pretty much the basic function, it’s a switch. Most integrated chips or IC’s as they are commonly called chips with several or many thousands of transistors inside. Computer processors are built up from millions of transistors. However, switching is not all a transistor can do, they can also be used as amplifiers.

The most basic transistor is probably a bipolar transistor and these transistors are made of three layers, which are the Emitter, Base and Collector.

Iif you wanted to control a relay with your computer you would need a transistor of this sort. The transistor would allow the very small current produced by your computer would go to the transistor’s base and emitter, which would allow the larger current on the emitter collector to flow to the relay.

Transistors of this sort have a few key features in common for instance the base – emitter junction and a diode will not conduct until the forward voltage exceeds 0.6 volts.

Too much current will cause a transistor to become hot and stop functioning. If a transistor is hot to the touch, disconnect the power it! Some project will force transistors to become hot and so proper heat sinks are connected to these transistors. Transistor meant for heavier loads will come with a metal tab on the back for mounting to a heat sink. A heat sink is black metal that is designed to dissipate the heat coming from these “power” transistors. As they relate to robotics heavy-duty motor controls (for motors 12 volt and up) you might see power transistors like this with heat sinks attached to them. Also power supplies often have these sort of transistors. Transistors of this sort are often MOSFET’s, which stands for Metal Oxide Semiconductor Field-Effect Transistor, or MOSFET for short. These transistor schematics symbols are picture to the right in the pervious schematics listing picture. MOSFET allow a few volts to switch or amplify many amperes at very fast speeds, this makes them perfect for control of larger motors.

The middle transistor schematics symbols are JFET’s or Junction Field-Effect Transistors. JFET’s can be used as amplifiers or switches just like all other transistors but they have a built in high resistance on their Gates (JFET’s don’t have an emitter, base and collector they have a source, gate and drain pins) so the have little effect on external components connect to their gates. If a JFET were used in the above relay circuit this would mean the computer would be even safer from voltage spikes. JFET’s are not often used for high power jobs.

INTERGRATED CIRCUITS

Integrated Circuits or IC’s for short reference are small electronics circuits contained inside a silicon chip. For instance an IC’s might have for build in transistor with 2 diodes and 2 resistors….this may never be displaced in the schematics symbols but that are build inside by tiny layers of silicon. IC’s are what make smaller electronics possible and what drive you computer; there are millions of different types of IC’s. At their most common core an IC is built up from basic transistors.

Integrated Circuits some in many different packages, the most common by far is the “dip” which stands for Dual In-line Package, in other words you have two rows of pins of a chip like this. Most IC’s will come with a little index marker, which will indicate which is pin 1, the marker looks like a little indented hole. DIP can range in pin count from 4 to 64. Most IC’s of this nature are clearly marked with the part number on them, such as 7404 or 555. Some schematic symbols for IC’s will look like the actual dip package with a box and the pins labeled and going to the other components of the circuit. This is the case with many schematics with 555 chips in them. However, most of the time the chip is cut up and parts of it are placed though out the circuit schematics. The cut up parts are the gates of the chips. The gates are like individual circuits inside the IC.

RELAYS and SPEAKERS

There are many different types of relays, but they all do the same things, which is to act like a switch. Inside a relay you’ll find a coil (as pictured) and an arrangement of contacts which provide different types of switching, such as SPST, SPDT and DPDT or Double Pole Double Through.

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BASIC ELEMENTS OF ELECTRONICS

BASIC ELEMENTS OF ELECTRONICS

An electronic component is a basic electronic element usually packaged in a discrete form with two or more connecting leads or metallic pads. Components are intended to be connected together, usually by soldering to a printed circuit board, to create an electronic circuit with a particular function (for example an amplifier, radio receiver, or oscillator). Components may be packaged singly (resistor, capacitor, transistor, diode etc.) or in more or less complex groups as integrated circuits (operational amplifier, resistor array, logic gate etc.)

Components

Electronic components are mechanically stabilized, improved in insulation properties and protected from environmental influence by being enclosed in synthetic resin.

Components major classification

1.Active Components.

2.Passive Components.

Power sources

Power source is an important device in Electronic Component without this on is work ie,all device require power for their work.

Discrete Passive Components

A passive component, depending on field, may either refer to a component that consumes (but does not produce) energy, or to a component that is incapable of power gain.

Passive components include capacitors, inductors, resistors, transformers, voltage sources, and current sources. They exclude devices like transistors, relays, glow tubes, tunnel diodes, and similar devices.

Discrete Active Components

Active components are those that have gain or directionality. They include Semiconductors (Diode, Transistors, Operational Amplifier and other Solid State Devices) and Thermionic Valves (Vacuum Tubes).

Test Equipments

This involves learning to read schematic diagrams, constructing circuit prototypes using breadboards, testing prototypes (using multimeters, oscilloscopes, and logic probes), revising prototypes (if needed), and constructing final circuits using various tools and special circuit boards.

Input Devices

Input devices convert physical signals, such as sound, light, and pressure, into electrical signals that circuits can use. These devices include microphones, phototransistors, switches, keyboards, thermistors, strain gauges, generators, and antennas.

Output Devices

Output devices convert electrical signals into physical signals.Output devices include lamps, LED and LCD displays, speakers, buzzers, motors (dc, servo, stepper), solenoids, and antennas.

Digital Circuits

Digital circuits work with only two voltage states, high (e.g., 5 V) or low (e.g., 0 V). The reason for having only two voltage states has to do with the ease of data (numbers, symbols, control information) processing and storage. The process of encoding information into signals that digital circuits can use involves combining bits (1’s and 0’s, equivalent to high and low voltages) into discrete-meaning “words.”

Bread Board(Socket Board) Connection

The bread board has many strips of metal (copper usually) which run underneath the board. These strips connect the holes on the top of the board. This makes it easy to connect components together to build circuits. To use the bread board, the legs of components are placed in the holes (the sockets). The holes are made so that they will hold the component in place. Each hole is connected to one of the metal strips running underneath the board.

Each wire forms a node. A node is a point in a circuit where two components are connected. Connections between different components are formed by putting their legs in a common node. On the bread board, a node is the row of holes that are connected by the strip of metal underneath .The long top and bottom row of holes are usually used for power supply connections.

For chips with many legs (ICs), place them in the middle of the board so that half of the legs are on one side of the middle line and half are on the other side.

The bread board has many strips of metal (copper usually) which run underneath the board.

These strips connect the holes on the top of the board. This makes it easy to connect components together to build circuits. To use the bread board, the legs of components are placed in the holes (the sockets). The holes are made so that they will hold the component in place. Each hole is connected to one of the metal strips running underneath the board.

Resistor Color Code

Capacitor Value

Connectors

Wires and cables provide low-resistance pathways for electric currents. Most electrical wires are made from copper or silver and typically are protected by an insulating coating of plastic, rubber, or lacquer. Cables consist of a number of individually insulated wires bound together to form a multi-conductor transmission line. Connectors, such as plugs, jacks, and adapters, are used as mating fasteners to join wires and cable with other electrical devices.

Wires

Cables

Switches

A switch is a mechanical device that interrupts or diverts electric current flow within a circuit. Switch can act as a interrupter, diverter. Other kinds of switches, such as push-button switches, rocker switches, magnetic reed switches.

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Resistors

Resistors

The resistor's function is to reduce the flow of electric current.
This symbol is used to indicate a resistor in a circuit diagram, known as a schematic.
Resistance value is designated in units called the "Ohm." A 1000 Ohm resistor is typically shown as 1K-Ohm ( kilo Ohm ), and 1000 K-Ohms is written as 1M-Ohm ( megohm ).

There are two classes of resistors; fixed resistors and the variable resistors. They are also classified according to the material from which they are made. The typical resistor is made of either carbon film or metal film. There are other types as well, but these are the most common.
The resistance value of the resistor is not the only thing to consider when selecting a resistor for use in a circuit. The "tolerance" and the electric power ratings of the resistor are also important.
The tolerance of a resistor denotes how close it is to the actual rated resistence value. For example, a ±5% tolerance would indicate a resistor that is within ±5% of the specified resistance value.
The power rating indicates how much power the resistor can safely tolerate. Just like you wouldn't use a 6 volt flashlight lamp to replace a burned out light in your house, you wouldn't use a 1/8 watt resistor when you should be using a 1/2 watt resistor.

The maximum rated power of the resistor is specified in Watts.
Power is calculated using the square of the current ( I² ) x the resistance value ( R ) of the resistor. If the maximum rating of the resistor is exceeded, it will become extremely hot, and even burn.
Resistors in electronic circuits are typicaly rated 1/8W, 1/4W, and 1/2W. 1/8W is almost always used in signal circuit applications.
When powering a light emitting diode, a comparatively large current flows through the resistor, so you need to consider the power rating of the resistor you choose.

Rating electric power

For example, to power a 5V circuit using a 12V supply, a three-terminal voltage regulator is usually used.
However, if you try to drop the voltage from 12V to 5V using only a resistor, then you need to calculate the power rating of the resistor as well as the resistance value.

At this time, the current consumed by the 5V circuit needs to be known.
Here are a few ways to find out how much current the circuit demands.
Assemble the circuit and measure the actual current used with a multi-meter.
Check the component's current use against a standard table.
Assume the current consumed is 100 mA (milliamps) in the following example.
7V must be dropped with the resistor. The resistance value of the resistor becomes 7V / 0.1A = 70(ohm). The consumption of electric power for this resistor becomes 0.1A x 0.1A x 70 ohm = 0.7W.
Generally, it's safe to choose a resistor which has a power rating of about twice the power consumption needed.

Resistance value

As for the standard resistance value, the values used can be divided like a logarithm. ( See the logarithm table )
For example, in the case of E3, The values [1], [2.2], [4.7] and [10] are used. They divide 10 into three, like a logarithm.
In the case of E6 : [1], [1.5], [2.2], [3.3], [4.7], [6.8], [10].
In the case of E12 : [1], [1.2], [1.5], [1.8], [2.2], [2.7], [3.3], [3.9], [4.7], [5.6], [6.8], [8.2], [10].
It is because of this that the resistance value is seen at a glance to be a discrete value.
The resistance value is displayed using the color code( the colored bars/the colored stripes ), because the average resistor is too small to have the value printed on it with numbers.
You had better learn the color code, because almost all resistors of 1/2W or less use the color code to display the resistance value.

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Fixed Resistors

A fixed resistor is one in which the value of its resistance cannot change.

Carbon film resistors

This is the most general purpose, cheap resistor. Usually the tolerance of the resistance value is ±5%. Power ratings of 1/8W, 1/4W and 1/2W are frequently used.
Carbon film resistors have a disadvantage; they tend to be electrically noisy. Metal film resistors are recommended for use in analog circuits. However, I have never experienced any problems with this noise.
The physical size of the different resistors are as follows.

From the top of the photograph 1/8W 1/4W 1/2W

Rough size Rating power (W) Thickness (mm) Length (mm) 1/8 2 3 1/4 2 6 1/2 3 9

This resistor is called a Single-In-Line(SIL) resistor network. It is made with many resistors of the same value, all in one package. One side of each resistor is connected with one side of all the other resistors inside. One example of its use would be to control the current in a circuit powering many light emitting diodes (LEDs).
In the photograph on the left, 8 resistors are housed in the package. Each of the leads on the package is one resistor. The ninth lead on the left side is the common lead. The face value of the resistance is printed. ( It depends on the supplier. )
Some resistor networks have a "4S" printed on the top of the resistor network. The 4S indicates that the package contains 4 independent resistors that are not wired together inside. The housing has eight leads instead of nine. The internal wiring of these typical resistor networks has been illustrated below. The size (black part) of the resistor network which I have is as follows: For the type with 9 leads, the thickness is 1.8 mm, the height 5mm, and the width 23 mm. For the types with 8 component leads, the thickness is 1.8 mm, the height 5 mm, and the width 20 mm.

Metal film resistors

Metal film resistors are used when a higher tolerance (more accurate value) is needed. They are much more accurate in value than carbon film resistors. They have about ±0.05% tolerance. They have about ±0.05% tolerance. I don't use any high tolerance resistors in my circuits. Resistors that are about ±1% are more than sufficient. Ni-Cr (Nichrome) seems to be used for the material of resistor. The metal film resistor is used for bridge circuits, filter circuits, and low-noise analog signal circuits.

From the top of the photograph 1/8W (tolerance ±1%) 1/4W (tolerance ±1%) 1W (tolerance ±5%) 2W (tolerance ±5%)

Rough size Rating power (W) Thickness (mm) Length (mm) 1/8 2 3 1/4 2 6 1 3.5 12 2 5 15

From :: http://www.interq.or.jp/japan/se-inoue/e_resistor.htm

Transistors

The transistor's finction is to amplify an electric current.
Many different kinds of transistors are used in analog circuits, for different reasons. This is not the case for digital circuits. In a digital circuit, only two values matter; on or off. The amplification abilitiy of a transistor is not relevant in a digital circuit. In many cases, a circuit is built with integrated circuits(ICs).
Transistors are often used in digital circuits as buffers to protect ICs. For example, when powering an electromagnetic switch (called a 'relay'), or when controlling a light emitting diode. (In my case.)

Two different symbols are used for the transistor.

PNP type and NPN type

The name (standard part number) of the transistor, as well as the type and the way it is used is shown below. 2SAXXXX PNP type high frequency 2SBXXXX PNP type low frequency 2SCXXXX NPN type high frequency 2SDXXXX NPN type low frequency The direction of the current flow differs between the PNP and NPN type. When the power supply is the side of the positive (plus), the NPN type is easy to use.

Appearance of the Transistor

The outward appearance of the transistor varies. Here, two kinds are shown.

On the left in the photograph is a 2SC1815 transistor, which is good for use in a digital circuit. They are inexpensive when I buy them in quantity. In Japan it costs 2,000 yen for a pack of 200 pieces. (About 10 US cents/piece in 1998)

On the right is a device which is used when a large current is to be handled. Its part number is 2SD880.





The electrical characteristics of each is as follows.

Item	2SC1815	2SD880
VCEO(V)	50	60
IC(mA)	150	3A
PC(mW)	400	30W
hFE	70 - 700	60 - 300
fT(MHz)	80	3

VCEO	:	The maximum voltage that can be handled across the collector(C) and emitter(E) when the base(B) is open. (Not connected) (It may be shown as VCE)
IC	:	The maximum collector(C) current.
PC	:	Maximum collector(C) loss that continuously can cause it consumed at surroundings temperature (Ta)=25°C (no radiator)
hFE	:	The current gain to DC at the emitter(E). (IC/IB)
fT	:	The maximum DC switching frequency. (the transision frequency)

Data sheet for 2SC1815