ECE301 Digital Design

Learning / Prototyping Objectives:

Introduction to reading circuit schematics: VCC, GND.

Familiarize with 3 specific circuit elements: Light Emitting Diode (LED), Resistor

(R), Power supply.

Build a simple LED circuit using a 330 Ohm resistor, red LED, and your 3V

battery pack.

Lab 1 Description:

In Lab 1, we will build the circuit shown in Schematic 1.

Introduction to breadboard-based prototyping: breadboard, jumpers, power rails,

connection rows.

3V

LAB1

330 Ω

RED

LED

Schematic 1:

This circuit will light up a

red Light Emitting Diode

(LED). The 3300 (Ohm)

resistor serves the

purpose of "limiting the

current going through the

LED. Without this resistor,

your LED would burn out.

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First of all let us define what "schematic" means. You can think of it as "a

connection diagram of circuit elements". In Lab 1, the circuit we will build is

depicted in Schematic 1, which shows three circuit elements that are connected to

each other in a certain way. These 3 circuit elements are shown below:/n330Ω

www

1

RESISTOR

Understanding

CATHODE

ANODE

Type

Resistor

ANODE

M

T.

POWER

LED

SOURCE

the parts required to build Schematic 1:

The circuit elements used in Schematic 1 are: 1) a 330 Ohm resistor, 2) a red LED,

and 3) a 3V voltage source. The following table summarizes these three elements:

Element #

CATHODE

3V

Value

330 Ω

Red

3 V

+

2

LED

3

Power source

Let us understand the circuit elements in detail:

Resistor is a two-terminal circuit element that is primarily used to control

voltage/current values. A terminal is the metal "leg" of the circuit element that is

used to make an electrical connection.

o In Schematic 1, the resistor limits the amount of current flowing through the

LED to avoid exposing the LED to a high amount of current, which will

destroy the LED.

o Resistor values are measured in Ohms, symbolized by the Greek letter

Omega (2). Some resistors have higher values than 1000 Ohm; so, instead

of calling it 10000, we call it 1k0 (pronounced kilo Ohm).

o The resistor used in Schematic 1 is 3300 (330 Ohms), which limits the LED

current at 3 mA (milli Amperes). This is a fairly low amount of current,

however, it will make the LED will be reasonably bright. Your LED will

consume 6 mW (milli Watts) while lit up.

o In Schematic 1, we could have called our resistor 0.33kQ, but this is

awkward; calling it 3300 is the standard practice.

Lights Emitting Diode (LED) is a circuit element that is used to "light up" to

indicate something happening, for example, your device in ON, etc. We see LEDS

in all electronic devices. They are probably one of the most useful electronic

circuit elements.

o The reason LEDs are called "Light Emitting Diode", rather than just "Light" is

that LEDS are in fact in are in the "diode" circuit element family. The

difference between an LED and an actual diode is the fact that the chemical/nstructure of an LED allows it to shine a visible light when current flows

through it. Because of this, the circuit symbol of a diode is identical to an

LED, with the exception of the additional lightning bolt next to the LED.

o The purpose of a diode is to flow the current only in one direction, but not in

the other (reverse) direction. Its "arrow" shape shows exactly which

direction the current flows in. Both diodes and LEDs share this property of

single-directional current flow; if you connect an LED in the opposite

direction, the current doesn't flow and your LED doesn't light up.

o While lit up, your LED will consume 6 mW (6 milli Watts) of power. Compare

this to the old-style incandescent light bulbs, which consume 60 W (60

Watts). Your LED consumes 10,000 times less power! No wonder you can

power the LED using a small battery pack!

Power source is a circuit element that provides a constant voltage at its two

terminals:

o vcc is the + terminal that has the "high" voltage. Since our battery pack is

3V, the Vcc terminal is always 3V (three volts); throughout the entire

ECE301 course, Vcc will mean 3V.

o

GND (Ground) is the terminal. This is the point in your circuit that has a

voltage level of OV (zero Volts).

Note that sometimes we refer to the power source as a "voltage source" or even

"energy source". They are interchangeable terms. An energy source stores a certain

amount of energy, which continuously loses a portion of the stored energy as you

use it to energize your circuit. If you use it long enough it will eventually run out of

energy and you will no longer be able to light up your LED.

How to setup your battery pack:

Take the two AA batteries provided in your lab kit and place them inside your

battery pack.

Each AA battery has a flat bottom, which is its - terminal and connects to the

springy metal.

Each AA battery also has a pointy top, which is its + terminal and connects to the

non-springy metal.

The battery pack has two cables coming out of it:

The RED cable is the 3V (the Yçç)

The Black cable is the OV (the GND)

The ON/OFF switch on top of the battery pack turns OFF the 3V supply when

we are not using the circuit. You must turn OFF your battery pack when you are

done with your experiment, since this will stop the energy drain on the battery

pack; if you forget to turn it OFF, your batteries will drain and you will need 2

new batteries !/nGathering the parts for building Schematic 1:

We will need a 3300 resistor, a red LED, and the battery pack to build Schematic 1.

You can locate them in your lab kit by following the information below:

3V Battery pack:

Your battery pack is

designed to provide a

constant 3V voltage by

serially-connecting two AA

batteries inside. Each AA

battery has a 1.5 V

voltage; connecting two of

them in series -inside the

battery pack- increases the

voltage of the battery pack

to 3V. This internal

structure of the battery

pack is not something we

will repeat beyond this lab,

since we only care about

the fact that the battery

pack itself provides 3V.

330 Resistor:

Resistors have color coding

on them, which allows you

to "read" their value by

deciphering the color code.

Color code of 330Qis:

Orange, orange, brown,

gold

Which translates to: 3300

±5%

5% tolerance means that

the resistance can be in

the range [313.5 ... 346.5]

Ohms

Red LED:

We are looking for an LED

that has a red color. If you

look "inside" the plastic

casing of the LED, you will

see a distinct pattern. One

HIGH ENERGY

Understand how to read Resistor Color Code:

https://en.wikipedia.org/wiki/

Electronic_color_code# Resistor_code

Learn more about LEDS:

https://en.wikipedia.org/wiki/Light-emitting_diode

RAYOVAC/nof its pins is called the

cathode and the other

anode. Cathode must be

connected to the lower

voltage (GND in our case)

and it looks like an

umbrella over the anode.

Building Schematic 1:

Now that we have the three parts we need, let us connect them and light up your

LED.

Before learning best practices, the

hard-wiring option shown on the right

is a bad way to build Schematic 1.

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As long as the electrical connections

of the three parts in Schematic 1 are

correct, the LED will light up. So, you

could very well get the 3300 resistor,

red LED, and the 3V battery pack and

connect them as shown on the right.

This is the "hard-wired" way of

connecting them. The anode of the

LED and one terminal of the 3300

resistor are "twisted together" to

connect them electrically. They are

ruined and you won't be able to use

them in the future labs.

The "hard-wiring" idea introduced above is terrible! Although hard-wiring will allow

you to demonstrate that Schematic 1 works, you just ruined one pin of the LED and

the resistor. Our intention is to use the parts in your kit over and over again

throughout the entire semester. The right way to build a prototype of Schematic 1 is

by using a breadboard (shown below)./nWe will use a breadboard to

build Schematic 1. A

breadboard is a

"prototyping" tool. It can be

thought of as a "temporary

connection board", which

allows you to build a working

version of the circuit,

demonstrate its functionality,

and disconnect everything

when done; after this

disconnection, all of the

original parts are intact and

can be used to demonstrate

a new circuit. The

breadboard prototype of

Schematic 1 is shown on the

right.

Understanding the Breadboard Vcc and GND Supply Rails:

Let us now understand how a breadboard works. For now, we will introduce some

elementary breadboard principles and will expand on them in the future labs. The

most important part of the breadboard is the VCC and GND supply rails. They are

indicated by the and signs.

The entire rail is connected electrically, supplying 50 (5x10) holes that can

connect your devices to the Ground (GND) pin, as shown below.

Similarly, the rail provides 50 holes for device terminals that need to be

connected to VCS:/nL

*****

GND

Vcc

*****

Additionally, there is a + and on the bottom.

50 pins on the top Vcc rail are connected to each other (the top + rail).

50 pins on the top GND rail are also connected to each other (the top

Notice that there is also a VCC and GND rail on the bottom.

The top XCC rail and the bottom XCC rail are not connected by default.

Similarly, the top GND rail and the bottom GND rail are not connected by default.

In Lab 1, we will only work with a single VCC and single GND supply rail. In Lab 2, we

will see how we can connect the top and the bottom rails to make longer (100-hole)

rails.

rail).

Understanding the Breadboard General Connections:

Although the VCC and GND supply rails are the most important parts of any circuit,

there are also many intermediate connections we have to establish. For this, the

breadboard has many options. Think of the breadboard as a connection matrix.

Excluding the supply rails, all of the other holes in the middle have a (Row, Column)

coordinate.

Top rows are numbered 1, ..., 5, ..., 60 ... Top columns are numbered A, B, C, D,

E./n.

L

Bottom rows are numbered 1, ..., 5, ..., 60 ... Bottom columns are numbered F,

G, H, I, J.

Columns A, B, C, D, E of any given row are connected to each other. So, for Row

6, columns A-E are connected; ie., 6A=6B=6C=6D=6E are the same electrical

connection! Shown as Top Row 6 below.

Every single hole in the Top Row 6 are connected to each other.

There are two other random examples shown below; Top Row 1 and Bottom Row

2. No particular reason for choosing any; just randomly chosen.

Top Row 1 holes are 1A=1B=1C=1D=1E; these 5 holes are connected to each

other.

Bottom Row 2 holes are 2F=2G=2H=21=2J. These 5 holes are also connected to

each other.

There is no connection from the top rows to the bottom rows. In other

words, for example, 2A and 2F are completely separate connections.

Top Vcc rail

Top GND rail

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BCDE

GHIJ

+

Top Row 1

Top Row 6

Bottom

Row 2

Bottom

Vcc rail

Bottom

GND rail

Understanding the Breadboard Prototype of Schematic 1:/nNow that we understand Vcc and GND rails, as well as the intermediate

connections, let us take a close look at the breadboard construction of Schematic 1,

which is shown below. The 3V battery pack's red cable (Vcc) is connected to the top

Xcc rail and its black cable (GND) is connected to the top GND rail. This will energize

our circuit and will bring the + and from the battery into the breadboard.

The cathode of the diode is connected to the GND rail (any one of the 50 holes will

be fine).

One terminal of the 3300 resistor is connected to the Vcc rail (any one of the 50

holes is fine).

E

+

F

B C D E

EU

ΕΠ

Looking at Schematic 1, we see that we still need the intermediate connection that

connects the second terminal of the 3300 resistor and the anode of the LED. We will

use one of the intermediate breadboard connections for this; the question is: which

one? The answer is always "whichever one is physically closer to the already

existing devices". If we look carefully at the already-made connections to the XCC

and GND supply rails, we are pretty close to the top rows (somewhere between Row