Robotics Episode 4 pot

The emitter is always forward biased with respect to the base so that it can supply a large number of majority carriers to its junction with the base.. The section on the other side of t

Tunnel Diode and Back Diode

in Figure 3.17:

FIGURE 3.17 Combination of tunneling current

and conventional P-N junction current resulting in

a composite characteristic which is the tunnel diode characteristic curve.

Current vs Voltage for a Tunnel Diode

Voltage (V)

1.4 1.2 1

0.6 0.8

0.4 0.2 0

The negative resistance region is the important characteristic for the tunnel diode In this region, as the voltage is increased, the current decreases; just the opposite of a conventional diode The most important specifi cations for the tun-nel diode are the Peak Voltage (Vp), Peak Current (Ip), Valley Voltage (Vv), and Valley Current (Iv)

Back Diode

A back diode is a tunnel diode with a suppressed Ip and so approximates a ventional diode characteristic See the comparison in the fi gures below:

con-TABLE 3.1 Typical Tunnel Diodes Supplied by American Microsemiconductor

C Capaci- tance Max.

(pF) (mA)

V P Peak Point Voltage Typ.

(mV)

V V Valley Voltage Typ.

(mV) (mV)

V fp Forward Peak Voltage Typ.

(GHz)

R S Series Resist.

Max.

(ohms)

-G Nega- tive Conduc- tance (mhosx- 10-3)

f RO Resis- tive Cutoff Frequ- ency Typ.

IBMON IBIAS

DATAN

CROSS POINT ADJUST CPA ALS

+

−

+

−

TABLE 3.2 Typical Ultra-high-speed Switching Tunnel Diodes Supplied by American

Microsemiconductor

Part

Number

I P Peak

point

current

(mA)

I V Valley Point Current (mA)

C Capaci- tance Max.

(pF) Max

(mV)

V P Peak Point Voltage (mV)

V V Valley Voltage Typical

l (mV)

V fp Forward Voltage Typica Typical

R S Series Resist.

Typical (ohms)

T Rise Time Typical (psec.)

Cathode (short lead flat side or spot)

The reverse breakdown for tunnel diodes is very low, typically 200 mV, and the TD conducts very heavily at the reverse breakdown voltage Referring to the

BD curve, the back diode conducts to a lesser degree in a forward direction It

is the operation between these two points that makes the back diode important Forward conduction begins at 300 mV (for germanium) and a voltage swing of only 500 mV is required for full-range operation

Defi nition: Light Emitting Diodes (LEDs) are compound semiconductor devices

that convert electricity to light when biased in the forward direction Because of its small size, ruggedness, fast switching, low power, and compatibility with integrated circuitry, LED was developed for many indicator-type applications

Today, advanced high-brightness LEDs are the next generation of lighting technology and are currently being installed in a variety of lighting applications

As a result of breakthroughs in material effi ciencies and optoelectronic ing design, LEDs are no longer used in just indicator lamps They are used as

packag-a light source for illuminpackag-ation for monochrompackag-atic packag-applicpackag-ations such packag-as trpackag-affi c signals, brake lights, and commercial signage

■ Compatible with integrated circuits

FIGURE 3.20 Parts of an LED.

Epoxy Body Wire Bond Die Die Cup Leads

TABLE 3.3 Semiconductors for LEDs

Green, Red Blue Red, Infrared Red, Infrared

Red Yellow, Red Blue Green Green

Red Yellow, Orange,

Red

Classifi cation: Classifi cation of LEDs are defi ned by spectrum.

(i) Visible LED: Based on max spectrum, produces red, orange, yellow, green,

blue, and white

(ii) Infrared LED: (IR LED).

Applications of LEDs

Visible LED: General-purpose application in various industries including

indi-cation devices for electronic appliances, measuring instruments, etc

Bi-color (dual color) LED: Charger for cellular phones, showcase boards,

traf-fi c boards on highways, etc

High & Ultra Brightness LED: Full-color display for indoor/outdoor,

au-tomotive signal lamps, high-mount lamps, indoor lamps, traffi c signal lamps, etc

Infrared LED: With high output capacity, IR LED is used in remote controls,

IrDa ( Infrared Data Storage Devices), etc

3.2.7 Transistors

A semiconductor device consisting of two P-N junctions formed by either a P-type or N-type semiconductor between a pair of opposite types is known as a transistor

A transistor in which two blocks of N-type semiconductors are separated by

a thin layer of P-type semiconductor is known as an NPN transistor

A transistor in which two blocks of P-type semiconductors are separated by

a thin layer of N-type semiconductor is known as a PNP transistor

The three portions of a transistor are the emitter, base, and collector, shown

as E, B, and C respectively in Figure 3.21

The section of the transistor that supplies a large number of majority ers is called the emitter The emitter is always forward biased with respect to the base so that it can supply a large number of majority carriers to its junction with the base The biasing of the emitter base junction of an NPN and PNP transistor

carri-is shown in Figure 3.22 Since the emitter carri-is to supply or inject a large amount of majority carriers into the base, it is heavily doped but moderate in size

The section on the other side of the transistor that collects the major portion

of the majority carriers supplied by the emitter is called the collector The tor base junction is always reverse biased Its main function is to remove major-ity carriers (or charges) from its junction with the base The biasing of collector base junctions of an NPN transistor and a PNP transistor is shown in Figure 3.21 above The collector is moderately doped but larger in size so that it can collect most of the majority carriers supplied by the emitter

collec-The middle section, which forms two P-N junctions between the emitter and collector, is called the base The base forms two circuits, one input circuit with emitter and the other an output circuit with collector The base emitter junction

is forward biased providing low resistance for the emitter circuit The base lector circuit is reversed biased, offering a high-resistance path to the collector circuit The base is lightly doped and very thin so that it can pass on most of the majority carriers supplied by the emitter to the collector

As the emitter base junction is forward biased, a large number of electrons (majority carriers) in the emitter (N-type region) are pushed toward the base

This constitutes the emitter current i .e. When these electrons enter the P-type

material (base), they tend to combine with holes Since the base is lightly doped and very thin, only a few electrons (less than 5%) combine with holes to consti-

tute base current i b The remaining electrons (more than 95%) diffuse across the thin base region and reach the collector space charge layer These electrons then come under the infl uence of the positively based N-region and are attracted or

collected by the collector This constitutes collector current i c

Thus, it is seen that almost the entire emitter current fl ows into the collector circuit However, to be more precise, the emitter current is the sum of the col-lector current and base current i.e.,

ie=ic+ib

Operation of a PNP Transistor

A PNP transistor circuit is shown in Figure 3.23 below The emitter base

junc-tion is forward biased while the collector base juncjunc-tion is reverse biased The

forward-biased voltage v eb is quite small, where as the reverse-biased voltage v cb

is considerably high

As the emitter base junction is forward biased, a large number of holes jority carriers) in the emitter (P-type semiconductor) are pushed toward the base This constitutes the emitter current i.e., when these electrons enter the N-type material (base), they tend to combine with electrons Since the base is lightly

(ma-FIGURE 3.23

EMITTER BASE COLLECTOR

P Forward biased

reverse biased

FIGURE 3.22

EMITTER BASE

N forward biased

reverse biased

COLLECTOR

doped and very thin, only a few holes (less than 5%) combine with electrons to

constitute base current i b The remaining holes (more than 95%) diffuse across the thin base region and reach the collector space charge layer These holes then come under the infl uence of the negatively based P-region and are attracted or

collected by the collector This constitutes collector current i c

Thus, it is seen that almost the entire emitter current fl ows into the collector circuit However, to be more precise, the emitter current is the sum of the col-lector current and base current i.e.,

Overview

■ ICs, often called “chips,” come in several shapes and sizes

■ Most common are 8-, 14-, or 16-pin dual in-line (dil) chips

■ ICs can be soldered directly into printed circuit boards, or may plug into sockets which have already been soldered into the board

■ When soldering, ensure that the IC (or the socket) is the correct way round and that no pins have been bent underneath the body

■ When fi tting new ICs it is often necessary to bend the pins in slightly, in order to fi t it into the board (or socket)

■ Some ICs are damaged by the static electricity that most people carry on their bodies They should be stored in conductive foam or wrapped in tin foil When handling them, discharge yourself periodically by touching some metalwork which is earthed, such as a radiator

Pin Numbering on a Typical IC

The value of the output voltage from simple power supplies is often not curate enough for some electronic circuits

ac-The power supply voltage can also vary due to changes in the main supply, or variations in the current taken by the load

3.2.9 Some Lab Components

While working with electronic circuits we generally come across so many tronic components that one needs to know Some of the components that are most common are described below:

elec-IC 7805

The 7805 supplies 5 volts at 1 amp maximum with an input of 7–25 volts The 7812 supplies 12 volts at 1 amp with an input of 14.5–30 volts

The 7815 supplies 15 volts at 1 amp with an input of 17.5–30 volts

The 7824 supplies 24 volts at 1 amp with an input of 27–38 volts

The 7905, 7912, 7915, and 7924 are similar but require a negative voltage in and give a negative voltage out

Note that the electrolytic 10 uF must be reversed for negative supplies sure that the working voltage of this component is suffi cient Say 25 V for the 5-, 12-, and 15-volt supplies and 63 V for the 24-volt supply

FIGURE 3.26 (a) 78 series (b) 79 series voltage regulators.

The other two capacitors can be 100 nF/100 volt working

The 78L series can supply 100 mA and the 78S can supply 2 amps

Eight Darlington Arrays

High-voltage High-current Darlington Transistor Array

■ Eight Darlingtons with common emitters

■ Output current to 500 mA

■ Output voltage to 50 V

■ Integral suppression diodes

■ Output can be programmed

FIGURE 3.27 ULN 2803.

FIGURE 3.28 ULN 2803 (pin connection).

2k7

+ A

■ Inputs pinned opposite outputs to simplify board layout.

■ Versions for all popular logic families

Description

The ULN2801A–ULN2805A each contain eight Darlington transistors with common emitters and integral suppression diodes for inductive loads Each Darlington features

a peak load current rating of 600 mA (500 mA continuous) and can withstand at least

50 V in the off state Outputs may be paralleled for higher current capability

The output of the ULN2803 is “inverted.” This means that a HIGH at the put becomes a LOW at the corresponding output line E.g., if the motor line con-nected to pin 1 goes HIGH, pin 18 on the ULN2803 will go LOW (switch off)

in-The ULN2803 is described as an “8-line driver.” This means that it

con-tains the circuitry to control eight individual output lines, each acting ently of the others The IC can be thought of as an 8-line ‘black box.’

independ-LM 324 IC

FIGURE 3.29 14-pin DIP

LM324—Quad Operational Amplifi er

■ The LM 324 is a QUAD OP-AMP.

■ Minimum supply voltage 6 V

■ Maximum supply voltage 15 V

■ Max current per output 15 mA

■ Maximum speed of operation 5 MHz

FIGURE 3.30 Pin diagram of ULN 2803.

1 2 3

4 5 6

9 10 11 12 13 14

3.3 STEPS TO DESIGN AND CREATE A PROJECT

A design procedure is a series of steps which guide you through any electronic design-and-make process Sticking to the procedure will help deliver a fi rst-class product

Once you have defi ned the purpose of your project, there are two important documents you need to write These are:

■ The design brief is a short statement of the problem to be solved The brief

should outline the design problem you are tackling, perhaps including one

or two of the envisaged design features

■ The design specifi cation is a longer document, including full details of the

functional and design features of the fi nished electronic product as well as information on weight and size, maintenance, cost, and safety

The specifi cation for an electronic product should include electronic factors such as component details, maximum working voltages, maximum currents, and temperature or frequency ranges

FIGURE 3.31

Following a design process

Choose an area of study

Prepare a design beief Write down a specification Carry out research

Use graphics, computer software and other techniques

to generate design ideas Select the best design for further development Write down in a few words the purpose of the project

Ergonomics and Aesthetics

The factors which make a product effi cient, safe, and comfortable to use are

called ergonomics Considerations of style—the things which make a product look and feel good—are called aesthetics You need to consider both ergonomic

and aesthetic factors when planning your designs

When designing circuits, for example, ensure that switches and other control components are placed so that they can be easily reached, and that output com-ponents such as LEDs can be easily seen

A product’s style is a more subjective matter, as different people may have different ideas of what looks good Think about contemporary style, about what

is currently fashionable, when designing your product You may not want to low the fashion, but you still need to know what it is!

Without sensors, a robot is just a machine Robots need sensors to deduce what

is happening in their world and to be able to react to changing situations This section introduces a variety of robotic sensors and explains their electrical use and practical application The sensor applications presented here are not meant

to be exhaustive, but merely to suggest some of the possibilities

Analog and Digital Sensors

There are two basic types of sensors: analog and digital The two are quite

different in function, in application, and in how they are used with the

Robo-Board An analog sensor produces a continuously varying output value over

its range of measurement For example, a particular photocell might have a resistance of 1k ohm in bright light and a resistance of 300k ohm in complete darkness Any value between these two is possible depending on the par-ticular light level present Digital sensors, on the other hand, have only two states, often called “on” and “off.” Perhaps the simplest example of a digital sensor is the touch switch A typical touch switch is an open circuit (infi nite

resistance) when it is not pressed, and a short circuit (zero resistance) when

it is depressed

Some sensors that produce a digital output are more complicated These

sen-sors produce pulse trains of transitions between the 0-volt state and the 5-volt

state With these types of sensors, the frequency characteristics or shape of this pulse train convey the sensor’s measurement An example of this type of sensor is the Sharp modulated infrared light detector With this sensor, the actual element-measuring light is an analog device, but signal-processing circuitry is integral to the sensor producing a digital output

Sensor Inputs on the RoboBoard

The RoboBoard contains input ports for both analog and digital sensors While both types of ports are sensitive to voltage, each type interprets the input voltage differently and provides different data to the microprocessor The analog ports measure the voltage and convert it to a number between 0 and 255, correspond-ing to input voltage levels between 0 and 5 volts The conversion scale is linear,

so a voltage of 2.5 volts would generate an output value of 127 or 128 The digital ports, however, convert an input voltage to just two output values, zero and one

If the voltage on a digital port is less than 2.5 volts, the output will be 0, while if the input is greater than 2.5 volts, the output will be 1 Thus, the conversion is very nonlinear

Reading Sensor Inputs

The C library function analog (port-#) is used to return the value of a particular analog sensor port For example, the IC statement

val = analog(27);

sets the value of the variable val equal to the output of port #27

Many devices used as digital sensors are wired to be active low, meaning that

they generate 0 volts when they are active (or true) The digital inputs on the boBoard have a pull-up resistor that makes the voltage input equal to 5 volts when nothing is connected A closed or depressed touch switch connected to a digital port would change that voltage to 0 volts by shorting the input to ground The resulting outputs: open switch = 1, and closed switch = 0, are the logical opposite

Ro-of what we usually want That is, we would prefer the output Ro-of the digital port to have value 0 or False normally, and change to 1 or True only when the switch hit something (like a wall or another robot) and was depressed The IC library func-tion digital (port-#), used to read a True-or-False value associated with a particular sensor port, performs this logical inversion of the signal measured on a digital port Hence, the depressed touch switch (measuring 0 volts on the hardware) causes the digital () function to return a 1 (logic True) or logical True value

For example, the C statement

if (digital(2)) do_it();

returns a True value (the number 1) and calls the function do_it() if the value at port #2 was 0 volts (indicating a depressed switch)

Connector Plug Standard

The standard plug confi guration used to connect sensors to the RoboBoard is shown in Figure 3.32 Notice that the plug is asymmetric (made by removing one

pin from a four-pin section of the male header), and is therefore polarized The

plug can only be inserted in the RoboBoard port in one orientation, so once the plug is wired correctly, it cannot be inserted into a sensor port backward This makes the plug much easier to use correctly, but, of course, if you wire it incor-rectly, you must rewire it since you cannot turn the plug around

Generally, the sensor is connected to the plug with three wires Two of the wires supply 5-volt power from the RoboBoard, labeled “+5v” and “Gnd.” The third wire, labeled “Signal” is the voltage output of the sensor It is the job of the sensor to use the power and ground connections (if necessary) and return its

“answer,” as a voltage, on the Signal wire

Sensor Wiring

Figure 3.33 shows a diagram of circuitry associated with each sensor This cuitry, residing on the RoboBoard, is replicated for each sensor input channel

cir-The key thing to notice is the pull-up resistor wired from the sensor input signal

leads to the 5-volt power supply

There are two reasons why this resistor is used First, it provides a default value for the sensor input—a value when no sensor is plugged in Many ICs, such

as those on the board that read and interpret the sensor voltage, do not perform

FIGURE 3.32 Generic sensor wiring.

Sensor Plug

Gnd +5v

Signal

sensor device