This is only a preview of the March 1989 issue of Silicon Chip. You can view 34 of the 96 pages in the full issue, including the advertisments. For full access, purchase the issue for $10.00 or subscribe for access to the latest issues. Articles in this series:
Articles in this series:
Items relevant to "Studio Series 32-Band Equaliser":
Articles in this series:
Articles in this series:
Articles in this series:
|
SILICON CHIP
Publisher & Editor-In-Chief
Leo Simpson, B.Bus.
Editor
Greg Swain, B.Sc.(Hons.)
Technical Staff
John Clarke, B.E.(Elec.)
Robert Flynn
Advertising Manager
Paul Buchtmann
Regular Contributors
Neville Williams, FIREE, VK2XV
Bryan Maher, M.E. B.Sc.
Jim Yalden, VK2YGY
Garry Cratt, VK2YBX
Jim Lawler, MTETIA
John Hill
David Whitby
Photography
Bob Donaldson
Editorial Advisory Panel
Philip Watson, MIREE, VK2ZPW
Norman Marks
Steve Payor, B.Sc., B.E.
SILICON CHIP is published 1 2 times
a year by Silicon Chip Publications Pty Ltd. All material
copyright (c). No part of the contents of this publication may be
reproduced without prior written
consent of the publisher. Kitset
suppliers may not photostat articles without written permission
of the publisher.
Typesetting/makeup: Magazine
Printers Pty Ltd, Waterloo, NSW
2017.
Printing: Masterprint Pty Ltd,
Dubbo, NSW 2830.
Distribution: Network Distribution
Company.
Subscription rate: currently $42
per year (12 issues) inside
Australia. For overseas rates,
refer to the subscription page in
this issue.
Liability: Devices or circuits
described in SILICON CHIP may be
covered by patents. SILICON CHIP
disclaims any liability for the infringement of such patents by the
manufacturing or selling of any
such equipment.
Address all mail to: Silicon Chip
Publications Pty Ltd, PO Box
139, Collaroy Beach, NSW
2097. Phone (02) 982 3935.
ISSN 1030-2662
* Recommended and maximum
Australian price only.
2
SILICON CHIP
PUBLISHER'S LE'l-l'ER
Deceiving the eye of
the beholder
This month we have a number of interesting constructional projects
in the magazine but the one which is most appealing to us is the LED
Message Board. We feel that this will be very popular among computer users because it is one of the few build-it-yourself computer
peripherals that is really useful.
Apart from its ability to be controlled by a personal computer, the
LED Message Board is intriguing because of its wide variety of visual
displays: scrolling up and down, wiping up and down and from side to
side, flashing words and so on. It is all made possible by clever programming of the Message Board's ZBOA microprocessor but there is
another interesting aspect - the use of multiplexed drive to the LEDs,
all 672 of them.
Multiplexed displays make use of the well-known persistence of vision of the human eye. If it were not for this persistence, movie films,
TV screens and fluorescent lamps would flicker badly and virtually
every digital display would be unreadable as the digits flashed individually on and off.
Multiplexing digital displays achieves two economies. First, it
reduces the power needed to produce a perceived brightness level in
the display and secondly, it greatly reduces the number of connecting
wires. In a typical 4-digit 7-segment display, a minimum of 11 drive
wires is required if multiplexing is used, compared with 32 if each
digit is driven separately.
That is a big reduction but consider the Message Board: with 672
LEDs it would need a phenomenal number of drive wires and it would
be difficult to get the variety of visual effects. With multiplexing and a
clever serial to parallel data conversion it only needs a minimum of 8
signal drive wires.
But perhaps the most intriguing aspect of the Message Board is not
all the clever driving circuitry but the way in which the observer must
"cooperate" with it in order to see the moving messages. Your eyes
must follow the words as they move from right to left or from left to
right. If you stare fixedly at one of these displays, you will only see a
jumble of lights.
So as well as exploiting the persistence of vision, message boards
also exploit the natural tendency of our eyes to constantly scan our
field of vision and to follow moving objects. Not only are our eyes being
deceived but they are cooperating in the process.
Leo Simpson
|