Elenco Understanding Logic Gates and Circuits User Manual

Outline

Page # Title Page # Title

3 Parts List 17 Project 10: S-R NAND Latch

4-7 Introduction 18 Project 11: Gated S-R Latch

8 Project 1: NOT Gate (Inverter) 19-20 Project 12: J-K Latch

9 Project 2: AND Gate 21-22 Project 13: Gated D Latch

10 Project 3: OR Gate 23-24 Project 14: Comparator

11 Project 4: NAND Gate 25 Project 15: Half Adder

12 Project 5: NOR Gate 26 Project 16: Half Subtractor

13 Project 6: Exclusive OR (XOR) Gate 27-28 Project 17: Multiplexer

2

14 Project 7: De Morgan’s Law

Negation of Conjunction

15 Project 8: De Morgan’s Law

Negation of Disjunction

16 Project 9: S-R NOR Latch

29-33 Quiz

34-41 Quiz Answers

Warning: Shock Hazard – Never connect Snap Circuits® to the electrical outlets in your home in any way!

Warning: Choking Hazard – Small parts. Not for children under 3 years.

Warning: Always check your wiring before turning on a circuit. Never leave a circuit unattended while the batteries are installed. Never connect

additional batteries or other power sources to your circuits. Discard any cracked or broken parts.

Batteries:

• Use only 1.5V AA type, alkaline batteries.

• Insert batteries with correct polarity.

• Do not mix old and new batteries.

• Remove batteries when they are used up.

• Do not short circuit the battery terminals.

• Non-rechargeable batteries should not be recharged.

Rechargeable batteries should only be charged under adult
supervision, and should not be recharged while in the product.

• Do not mix alkaline, standard (carbon-zinc), or rechargeable

(nickel-cadmium) batteries.

• Do not connect batteries or battery holder in parallel.

• Never throw batteries in a fire or

attempt to open its outer casing.

• Batteries are harmful if swallowed,

so keep away from small children.

Parts List

ID Part Name Part Number QTY
1 1-snap wire 6SC01 7
2 2-snap wire 6SC02 10
3 3-snap wire 6SC03 5
4 4-snap wire 6SC04 1
5 5-snap wire 6SC05 2
6 6-snap wire 6SC06 1
7 7-snap wire 6SC07 2
B1 Battery Holder 4.5V (3-AA) 6SCB3 1

Base Grid (11.0” x 7.7”) 6SCBG 1

D1 LED red 6SCD1 1
D2 LED green 6SCD2 1

Jumper wire black 6SCJ1 1
Jumper wire red 6SCJ2 1
Jumper wire orange 6SCJ3A 1
Jumper wire green 6SCJ3C 3
Jumper wire gray 6SCJ3E 5

R2
S1 Slide switch 6SCS1 1
U15 NOT Gate 6SCU15 3
U16 AND Gate 6SCU16 2
U17 OR Gate 6SCU17 1
U18 NAND Gate 6SCU18 2
U19 NOR Gate 6SCU19 2
U20 XOR Gate 6SCU20 1

1kΩ Resistor

6SCR2 2

3

Introduction

Analog signals can take on a continuum of values while

Analog vs. Digital Waveforms

 Analog Waveform – can take on any voltage value

Voltage

4

Analog Signal

takes on a

Continuum of

Voltage values

5
4
3
2
1
0

Time

 Digital Waveform – takes on discrete voltage values

Voltage

5

Example of Digital

Signal taking on two

discrete values

(0 Volts and 5 Volts)

0

Time

digital signals take on only discrete values.

Introduction

Digital Signals

 Digital waveforms can be used to represent digital

signals (e.g. 0 or 1, true or false), for example

• 0 (false) – represented by 0 Volts

• 1 (true) – represented by a small voltage, e.g. 3 Volts

 Example of Digital Waveform representing digital

5

signals

3V

0V

Digital signals are represented by a “high” state (1) or “true” state consisting of a small voltage

(e.g. 3V) and “low” state (0) or “false” state consisting of 0 Volts.

True

1 0 0 1 0 1 1 0

False

False

True

False

True

True

False

Time

Introduction

only if both inputs are true (batteries are not dead AND it’s the top of the hour).

Logic Problem Statements

 Logic problems have outcomes (or outputs) that depend on events

(or inputs).

 For example

• The cuckoo clock makes noise if the batteries are not dead AND it’s the top of

the hour.

• In this example, the output is “the cuckoo clock making noise” and the inputs

are “the batteries are not dead” and “it’s the top of the hour”.

6

Batteries not dead?

Top of the hour?

Decision

Cuckoo clock makes noise?

Box

• Note that in this example, the output is true (cuckoo clock makes noise) if and

• You will see that this decision box can be represented by digital logic using an

AND gate, with the inputs and output being represented by digital signals.

You can think of digital logic gates as decision boxes that solve logic problems.

Introduction

Logic Gates

 A digital logic gate is an Integrated Circuit (IC) device that

makes logical decisions based on various combinations of
digital signals presented to it’s inputs.

 Digital logic gates can have more than one input signal,

but generally have a single output signal, just like the
decision box on the previous slide.

 In the following projects, the input digital signals will be

represented by A and/or B and the output digital signal
will be represented by Q.

7

 The next six projects will demonstrate how the output

Input Digital

digital signal is determined by the input digital signals for
various different digital logic gates (NOT gate, AND gate,

Signals

Output Digital

Signal

OR gate, NAND gate, NOR gate, XOR gate).

A

Digital Logic

 The remaining projects will demonstrate the input/output

Gate

characteristics of some common combinations of digital

B

logic gates, called digital logic circuits.

Almost all modern electronics such as computers and cellphones use digital logic circuitry.

Q

Project 1: NOT Gate (Inverter)

8

1

0

2

1

3

This circuit demonstrates how the NOT
Gate (U15) works. Turn the slide switch
(S1) on. Connect the loose end of the

A

2

2

U15

1

Q

1

2

1

red wire to either low voltage (denoted
as a “0”) or high voltage (denoted as
“1”). If input A is low (0), then the Q
output will be high (1), and the red LED
(D1) will be on. If input A is high (1),
then the Q output will be low (0) and

3

2

2

1

2

3

1

2

the red LED will be off.

A

Q

The inversion of a state is often
represented with a bar over the

variable, so Q = A.

Input (A) Output (Q)

0 1

1 0

NOT gates are used in digital logic circuits to “invert a voltage level”. A high voltage level (1)

into the NOT gate becomes a low voltage level (0) at the output and vice versa.

1

0

9

Project 2: AND Gate

This circuit demonstrates how the AND

2

1

2

3

A

2

B

1

2

1

2

3

Q

U16

1

2

2

2

1

3

1

2

Gate (U16) works. Turn the slide switch
(S1) on. Connect the loose ends of the red
and black wires to either low voltage
(denoted as a “0”) or high voltage
(denoted as a “1”). If, and only if, both
input A AND input B are high (both 1s),
then the Q output will be high (1), and the
red LED (D1) will be on.

A

Q

B

The output of an AND gate is often
represented as the product of the

inputs, so Q = AB.

Input (A) Input (B) Output (Q)

0 0 0

0 1 0

1 0 0

1 1 1

AND gates are used in digital logic circuits to perform a logical multiply. When one of the inputs is low (0),

the output is low (i.e. multiply by 0). The output will only be high (1) when both inputs are high.

1

0

10

Project 3: OR Gate

2

This circuit demonstrates how the OR Gate

1

2

A

2

B

1

2

1

2

3

Q

2

2

3

(U17) works. Turn the slide switch (S1) on.
Connect the loose ends of the red and
black wires to either low voltage (denoted
as a “0”) or high voltage (denoted as a

U17

“1”). If either input A OR input B are high

1

2

1

(1), then the Q output will be high (1), and
the red LED (D1) will be on.

1

A

Q

B

2

3

The output of an OR gate is often
represented as the sum of the inputs, so

Q = A+B.

Input (A) Input (B) Output (Q)

0 0 0

0 1 1

1 0 1

1 1 1

OR gates are used in digital logic circuits to perform a logical add. When one of the inputs is high (1), the

output is high. The output will only be low (0) when both inputs are low.

Project 4: NAND Gate

11

1

0

2

1

3

This circuit demonstrates how the NAND
Gate (U18) works. Turn the slide switch (S1)
on. Connect the loose ends of the red and

2

A

2

B

1

2

U18

1

2

1

black wires to either low voltage (denoted as
a “0”) or high voltage (denoted as a “1”). If
either input A OR input B are low (0), then
the Q output on U18 will be high (1), and the
red LED (D1) will be on. The output logic is
exactly the opposite of the AND gate, hence

3

Q

2

2

1

2

3

1

this gate is called the NOT AND or NAND
Gate.

2

A

Q

B

Input (A) Input (B) Output (Q)

0 0 1

0 1 1

1 0 1

1 1 0

NAND gates are used in digital logic circuits to perform an inverted logical multiply. When one of the

inputs is low (0), the output is high. The output will only be low (0) when both inputs are high.

Project 5: NOR Gate

12

1

0

2

1

2

3

A

2

B

1

2

U19

1

2

1

This circuit demonstrates how the NOR Gate
(U19) works. Turn the slide switch (S1) on.
Connect the loose ends of the red and black
wires to either low voltage (denoted as a
“0”) or high voltage (denoted as a “1”). If,
and only if, both input A AND input B are
low (0), then the Q output on U19 will be
high (1), and the red LED (D1) will be on.

3

Q

2

2

1

2

3

1

2

The output logic is exactly the opposite of
the OR gate, hence this gate is called the

NOT OR or NOR Gate.

A

Q

B

Input (A) Input (B) Output (Q)

0 0 1

0 1 0

1 0 0

1 1 0

NOR gates are used in digital logic circuits to perform an inverted logical add. When one of the inputs is

high (1), the output is low. The output will only be high (1) when both inputs are low.

Project 6: Exclusive OR (XOR) Gate

2

13

1

0

1

2

A

2

B

1

2

3

This circuit demonstrates how the Exclusive
OR (XOR) Gate (U20) works. Turn the slide
switch (S1) on. Connect the loose ends of
the red and black wires to either low voltage

U20

1

2

1

(denoted as a “0”) or high voltage (denoted
as a “1”). If input A and input B are

exclusive (i.e. different), then the Q output

3

Q

2

2

1

2

3

1

2

on U20 will be high (1), and the red LED (D1)
will be on.

A

Q

B

Input (A) Input (B) Output (Q)

0 0 0

0 1 1

1 0 1

1 1 0

XOR gates are used in digital logic circuits to perform a comparison. When the inputs are mutually exclusive

(i.e. different), then the output is high (1). When the inputs are the same, then the output is low (0).