COURSE PROJECT OF ELECTRICAL AND

ELECTRONICS TECHNOLOGY REPORT

Digital Electronic Clock

Aeronautical Engineering Department

Class no. 1911611 / 1911612

Project By :

1.古尼尔 (Cornellius K) – 191161112

2.黄天福 (Metin Uengprasert) – 191161201

July 2, 2013

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Preface

Digital electronic clock is a timing device with a digital display. It has benefits with a high precision (no analog outputs / circuitry), and with a digital visual output. In a common digital clock, there are second, minute, hour, and week counters.

The purpose of this project is to make students understand how to connect decoders, displays, counters, and timers to the bread board. Students should understand the characteristics of the bread board (horizontal and vertical electrical conductivity), how to organize the circuitry to make it efficient, and characters of every chips used in the system so every student can wire it properly.

We also understand that wiring is an art which has a systematic and colorful way of connection that makes the overall circuit look presentable and easy to follow where the connection starts, leads to and ends.

Our digital clock contains displays LC5011-11, decoders, counters and timer. Some of the chips used in the system are the common 7400 series chips such as 74LS247, 74LS74, 74LS20 and 74LS90.

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Contents

Requirements3

Framework of The System4

Reference Circuit and its Principle 6-12

Reference Circuit 6

Bread Board 6

7-Segment Display7

7-Segment Decoder (74LS247)7

Dual D flip-flop (74LS74)8

“NAND” Gate (74LS20)8

Counter (74LS90) 9

Timer (555) 9

Resistor 10

Modulo-60 Counter and Modulo-24 Counter11

Modulo-7 Counter 12

Problems13

3

Problem Solving14

Advice and Expectation14

List of Apparatus and Equipments15

Reference15

Requirements

The digital electronic clock requires 5 displays on the bread board and it must display second and minute (modulo-60) counter displaying number from 00 to 59, hour (modulo-24) counter displaying number from 00-23, and week (modulo-7) counter displaying number from 1-6 for Monday until Saturday and 8 for Sunday.

All we have to do is assemble the displays, decoders and counters to the bread board, providing power and grounding, and inputting the frequency to the system to make it run.

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Framework of The System

5

TimerSignal or continuous pulse

Second

Correction

Hour

Correction

Minute

Correction

Second (60) Counter

Decoder

Display

Minute(60) Counter

Decoder

Display

Week

Correction

Hour(24) Counter

Decoder

Display

Week(7) Counter

Decoder

Display

Reference Circuit and its Principle

Reference Circuit

Bread Board

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A breadboard is a construction base for prototyping of electronics. The term is commonly used to refer to solderless breadboard.

Because of the solderless breadboard does not require soldering, it is reusable. This makes it easy to use for creating temporary prototypes and experimenting with circuit design. A variety of electronic systems may be prototyped by using breadboards, from small analog and digital circuits to complete central processing units (CPUs).

7-Segment Display

A seven-segment display (SSD), or seven-segment indicator, is a form of electronic display device for displaying decimal numerals that is an alternative to the more complex dot-matrix displays. Seven-segment displays are widely used in digital clocks, electronic meters, and other electronic devices for displaying numerical information.

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g f 共 a b

e d 共 c Dp

Power pin

Power pin

7-Segment Decoder (74LS247)

The 74LS247 IC has four input leads to which the 4-bit BCD numbers are applied. Each input is labeled with a capital letter, which represents one of the binary-weighted positional values.

The seven output leads of the 74LS247 IC, labeled a-g, connect to the seven input leads of the display that have the same letter. These outputs are active-low, which is indicated by the overbar at each letter and by the circle at each lead.

Dual D flip-flop (74LS74)

The 74LS74 is one of a set of integrated circuits in the 7400 family. It is a microchip that acts like a switch. It has 1 byte of memory to remember the status when it was last triggered. The “Dual Flip Flop” means there are two of these identical “switches” contained in the chip package. More modern variations of this unit are seen in many electronics devices, especially robotics.

“NAND” Gate (74LS20)

This device contains two independent gates, each of which performs the logic NAND function. The Negated AND, NOT AND or NAND gate is the opposite of the digital AND gate, and behaves in a manner that corresponds to the

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16 15 14 13 12 11 10 9

1 2 3 4 5 6 7 8

74LS247

Vcc f g a b c d e

B C LT I /Y I D A GNDB BR BR

14 13 12 11 10 9 8

1 2 3 4 5 6 7

74LS74

Vcc 2R 2D 2CP 2S 2Q 2QD D

1R 1D 1CP 1S 1Q 1Q GNDD D

14 13 12 11 10 9 8

1 2 3 4 5 6 7

74LS20

1A 1B NC 1C 1D 1Y GND

Vcc 2D 2C NC 2B 2A 2Y

opposite of AND gate. A LOW (0) output results only if both the inputs to the gate are HIGH (1); if one or both inputs are LOW (0), a HIGH (1) output results.

Counter (74LS90)

The 74LS90 is a decade counter, meaning it is able to count from 0 to 9 cyclically, and that is its natural mode. That is Qa, Qb, Qc and Qd are 4 bits in a binary number, and these pins cycle through 0 to 9.

You can also set the chip up to count up to other maximum numbers and then return to zero. You “set it up” by changing the wiring of the R0(1), R0(2), R9(1) and R9(2) lines. If both R0(1) and R0(2) are 1 (5 volts) and either R9(1) or R9(2) are 0 (ground), then the chip will reset Qa, Qb, Qc and Qd to 0. If both R9(1) and R9(2) are 1 (5 volts), then the count on Qa, Qb, Qc and Qd goes to 1001.

Timer (555)

9

14 13 12 11 10 9 8

1 2 3 4 5 6 7

74LS90

CPA NC Qa Qd GND Qb Qc

CPB R (1) R (2) NC Vcc R (1) R (2) 0 0 9 9

8 7 6 5

1 2 3 4

555

Vcc DIS TH CO

GND TR OUT RD

The 555 timer IC is an integrated circuit (chip) used in a variety of timer, pulse generation and oscillator applications. The 555 can be used to provide time delays, as an oscillator, and as a flip-flop element. Derivatives provide up to four timing circuits in one package.

Introduced in 1971 by Signetics, the 555 is still in widespread use due to its ease of use, low price and good

stability.

Internally, the 555 Timer IC provides 2 comparators, one for the input signal and the other for the capacitor voltage, and a flip-flop and output driver. Since the comparator reference voltage is chosen as a fixed ratio of the Vcc voltage, the timing is independent of the supply voltage. The 555 Timer IC’s key components are the 2 resistors and the 1 capacitor. The 2 components assist in providing the periodic waveform based on the charging/discharging of the voltage applied to the circuit network at pins 2(Trigger) and 7(Discharge).

Resistor (4 color rings)

We use the resistor to increase the resistance in

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8 7 6 5

1 2 3 4

555

Vcc DIS TH CO

GND TR OUT RD

Multiplier

Error

Second digit

First digit

the 7-segment display to avoid the damage in the display caused by great number of electric current. In this system, we used the orange black brown gold resistor which resistance is 300Ω.

Modulo-60 Counter and Modulo-24 Counter

Both second and minute counter is modulo-60 counter displaying number from 0 to 59; hour counter is modulo-24 counter displaying number from 0 to 23. The reference circuits designed with 74LS90 are shown in 4 Figures below.

(Decimal counter) (modulo-6 counter)

(modulo-60 counter)

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(modulo-24 counter)

Modulo-7 Counter

Week counter is modulo-7 counter displaying number from 1 to 6 and then 8 in accordance with people’s habits (using

日 from 星期日[Sunday]). Its truth table is shown in Table below. The reference circuit designed with 74LS74 is shown in Figure below.

Qd Qc Qb Qa display 0 0 0 1 Monday (1)

0 0 1 0 Tuesday (2)0 0 1 1 Wednesday (3)0 1 0 0 Thursday (4)0 1 0 1 Friday (5)0 1 1 0 Saturday (6)1 0 0 0 Sunday(8)

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Problems1) Lots of wiring leads into untidy wire arrangement. Do

the shortest connections first.2) Need to remember what each pins represent.3) Easy to connect, but the work is a little bit tedious.4) The IC chips label is not clearly visible.5) Some of the IC chips pins were bent.6) When cutting the plastic coating, we had to make sure

that the exposed wire is long enough to reach the conductor, around one centimeter.

7) It was not easy to peel the plastic coating of the wire.8) We was confident that our circuit will work, but it was

not working well in the end. We need to debug it for around 2 hours trying to find what’s wrong.

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Problem Solving1) Be extra careful when wiring.2) Make a wiring plan to avoid crossing wires.3) Color-code the connections, it’s easier to debug that

way.4) Check the labels on the IC chips under well-lit light.5) Carefully straighten the bent pins. 6) Ask the instructor to check for the broken chips.7) Ask the instructor to assist when using frequency

generator.

Advice and Expectation1) Listen carefully in the introduction class when the

instructor explains all about the experiment.2) Be patient with the bread board as it is a bit tedious

dealing with the wires.3) Plan your circuitry ahead to avoid crossing wires. 4) Understand how each chip works, represents, and how

the bread board works.5) Be patient with the debugging. It could just be a

problem in the components especially chips and displays.

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If you follow all of these advices, you surely can assemble this digital electronic clock project easily.

List of Apparatus and Equipments

No.

Name Spec. Quantity

1 DC Source 12 7-Segment

DisplayLC5011-11(common

anode)5

3 7-Segment Decoder

74LS247 5

4 Dual D flip-flop

74LS74 2

5 2 x four inputs

“NAND” gate

74LS20 1

6 Counter 74LS90 4

7 Resistor 300Ω (orange black brown gold)

5

8 Bread board 19 Tweezers,

scissors1

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Reference· 数字电子钟 – PPT

· www.howstuffworks.com

· en.wikipedia.org

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