12/15/12 Digital Stopwatch 0-99sec

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Digital Stopwatch 0-99sec

author: Pafilis Ioannis - Aristotle University of ThessalonikiDepartment of Electronics and Telecommunications

Introduction

In the present article, we will describe the function of a digital stopwatch, 0 99

the use of 4 integrated circuits, which in this case belong to National Semiconductor (httpintegrated circuits can be used to achieve the same result, however in this case we have used the following parts

Α. 1 x CD4060BM (14 stage ripple carry binary counter)B. 1 x CD4040BM (14 stage ripple carry binary counter)

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C. 1 x MC14518B (BCD counter)D. 2 x MC14511B (BCD to seven segment driver)E. 2 x 7 segment LED displays

The circuit that has been used is shown in picture 1. Through the experimental part we will explain each of the parts functionorder to have a notion of the basic idea, let just say, that this circuit besides the 5V power supply, is fed with a pulse from a crystal. The crystals pulse is devided properly in order to obtain the 1 Hz pulse which we need in order properly, and display the seconds on the 7 segment displays, through a procedure which we will explain part.

Description

We will begin the description of the digital circuit above. For our convenience we will devide the circuit togenerator, which produces the pulse of the desired frequency, and the part that does the actual counting.

Generator: The generator of the circuit comprises of theintegrated circuits CD4040CM and CD4060CM. We use a

signal has a frequency of 4,194,304Hz, we take a signal,which has a frequency of 256Hz

12/15/12 Digital Stopwatch 0-99sec

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crystal which oscillates at a frequency of 4,194,304MHz.It is obvious that this frequency is completely useless, asit is too big to be used as it is to our circuit. What weshould is devide this frequency, in a way that in its finalform, the pulse will have a frequency of 1Hz, which is thedesirable frequency. Initially we use the integratedCD4060, which devides the imported frequency in itsinput, by forces of 2. As we can see on the integratedcircuit the outputs are marked as Q4, Q5, Qn. Byimporting a pulse in the CLK input of the 4060, with afrequency f Hz, we take out of output Qn, a signal which

has a frequency equal to f/2n,. So, by exporting the signalout of Q14, knowing that the imported

By importing this signal through Q8 we have finally taken at the frequency of 1Hz. The fact that firstly doesnt affect the proper secondly is due to the inversion can see. This inversion just causesbe triggered with a logical 0. By output, we have a visual of the pulse the diode polarizes through it.

Counter: The signal of 1Hz, which we have taken fromthe generator, is imported to a BCD counter MC14518.This integrated circuit adds a logical 1 at each pulse, onits output.του. .The MC14518 is virtually divided into twosegment. One counts the units of the seconds, while theother the decades. As we can see in picture 1, thegenerators pulse is imported to the part which counts theunits. This is very logical, as we want in each secont thenumber of the display to be raised by 1. On the otherhand, we want the first display to raise by 1, every 10seconds. This is why, we ground the CLK input, and weuse the signal of Q3 to the CKE input.

By using this means, we make sure that the first displaywill be triggered, only when we have a decreasing signal onQ3; that is, only when the signal drops from logical 1 tological 0. As we can see, the first display increments every10 seconds, which means that after 9 on the seconddisplay (1001 on the display must be set to +1. That is that from descending pulse, as the last digit to logical 0 and triggers the BCD When the decades display becomes 9 goes to the next state, which is zero, and begins once more.

The integrated circuits MC14511 are BCD to 7 segment drivers. As its name clearly state, their sole purpose is to translate the BCD

information of MC14518, to a code understandable by the 7 segment displays. The inputs test the LEDs of the display and pulse modulate the brightness of the display. In this case we these inputs to logical need them. The LE input (Latch Enable) is used to keep the number of the displays while the pulse still runs. It is similar to the one of the modern stopwatches.

In addition, at any given moment we can restart the counting, by pressing the reset switch. By this means we set the input of the MC14518 to logical 1, which resets the counting to 0000.

Also check the Digital Stopwatch 0-60sec

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