Classic Mode

Star Tech Journal

Issue: 1983-November - Vol 5 Issue 9

7
STAR*TECH JOURNAL/NOVEMBER 1983
"Rally Video Car" continued from page 7.
blue field. CRASH is an enable pulse ( approx.
3-4 seconds duration) that causes the red
flashing of the screen when the driver crashes.
The flashing is at a 14Hz rate as controlled by
the 14Hz signal present on pin 2 of M4.
The function described above is the same
for green and blue circuits. It is important to
know that not all of the signals put color on the
screen. For example, to get a yellow car we
need 50% red and 50% green. In the red circuit
we see CAR4 present on pin 3 of L2. This
signal causes L2 to output a signal to generate a
small red car during a particular period of scan.
CAR4 on pin I of M2 in the green circuit will
cause a small green car to be generated at the
same location and during the same period of
~ that generated by the red circuit (L2).
CAR4 on pin 12 ofL3 (by passing the require-
ments of a NAND gate) is essentially being
inverted by that gate giving us CAR4 at pin 8 of
L3 (CAR4 inverted). CAR4 enters M2 of the
blue circuit at the same time ( forgetting about
propagation delays), as CAR4 enters the green
section of M2 (pin I) and the red section of L2
(pin 3). Since M2 and L2 are inverting gates,
the outputs of these gates are: L2, red, CAR4;
M2, green, CAR4; M2, blue CAR4. The
sections ofM3 are non-inverting and the moni-
tor sees signals that tell the CRT itself to emit a
red signal (active Hi CAR4), a green signal
( active Hi, CAR 4) which yields yellow ( 50%
red, 50% green). While this occurs our CAR4
on the blue gun tells the CRT to inhibit
emission of electrons to the blue phosphors
during the times when the yellow car is being
constructed.
I could have made this more confusing by
including the other signals that are present on
the inputs of these gates, but that would entail
Boulean Algebra and unnecessary confusion.
The principle of operation, however, is there
and the same thought flow can be used to
troubleshoot any problem the screen indicates.
This technique can be applied to any video
game.
The second basic function of the video
circuit is to produce what is known as the Y-
signal. The Y-signal is simply a combined
version of the 3 chroma signals. This signal
would generate luminance on the screen or, in
other words, brightness. It is also the black and
white portion of the picture. This signal is
present on all color picture reproducing devices.
If you turn the color level down fully on your
color TV receiver, you are observing the Y-
signal. If you tum the color up all the way
( excessive color) and then back the brightness
down to low luminance, you now see mostly
chroma or color signals. By adjusting these 2
controls, one can adjust the picture for high
quality resolution.
The Y-signal is applied to the cathode of the
CRT itself. The transistor Ql amplifies the
combined chroma signal through the three
resistors located at the base of Q 1. Sync
applied through D 1 is used to blank the picture
( shut off the Y-signal) during retrace.
Being an ex-television technician, I have
stared into fuzzy, splotchy, hazy screens for
hours and I fully believe in" a picture is worth a
thousand words." Determining where to start
looking by observing the screen can only be
done with an understanding of what goes on
inside. This series of articles will prove to
simplify this video game and hopefully others.
800/553-8000 reaches our service depart-
ment which is dedicated to decreasing, if not
eliminating, loss ofrevenue due to "down"time.
We encourage all owners and technicians to
call us between 8:15 a.m. and 5:00 p.m.
Monday through Friday to ask any question
concerning products we distribute.
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8
STAR*TECH JOURNAL/NOVEMBER 1983
PRICE
CONVERSION
BREAKTHROUGH!
FOR ROWE
CIGARETTE
MACHINES
• Will vend up to $1.75 in
increments of 5¢.
• Same mechanical
dependability using your
present totalizer. No
electronic components.
• Accepts any combination of
nickels, dimes and quarters.
• 4-minute installation on
location OR
• Send us your totalizer - we
will convert it ($5.00 service
charge).
?·SEGMENT DISPLAYS
By Mark "Bear" Attebery, Vending International Corp., San Juan Capistrano, CA
Hello out there techs and future techs. I'm in a
super mood this month because I now have
substantial proof that lots of experienced techs
also read my future tech articles! What proof,
you ask? Well, whether it was a typographical
error, or just that I pushed the wrong buttons
when finding the answers for the 10 work
problems in September's The "Bear" Facts
(S*TJVol. 5/#7) I don't know. But I do know
that a lot of techs called and let me know that
the answers to problems 3 and 10 were incorrect!
Here are the correct answers for any of you
who were hesitant about calling me and saying
"It ain't right!"
Problem #3's answers should read RT=
5.397k and that makes the IT = 3.335mA.
Problem# lO's answers should read RT=
8.090k and that makes the IT = l .483mA.
On to Future Tech Lesson #9. There are a
lot of CMOS applications that use LED or
LCD 7-segment displays. Everything from
wristwatches to arcade games use digital
displays, and since you can have so many
functions on a CMOS IC, they are very useful
for both space and design time savings. Case in
point! Cinematronics' laser disc game Dragon's
Lair uses an LED score display for player 1
and 2 scores, number of lives left for each
player, number of credits, etc. All of the logic
functions, driving functions, decoding functions,
etc., are done by two highly intelligent IC
chips. This chip is produced by INTERSIL
and is not a custom IC, but is known as the
ICM7218D IJI IC chip. By the way, both chips
are the same part number.
If you were using SSilogic to drive these 16
or so 7-segment LEDs, it would take 30 or
more chips to do the same function. So, for
troubleshooting purposes, design time, space,
and a lot of other reasons, CMOS chips are
widely accepted for use with digital displays.
A typical example of how a digital display
is driven is as follows: Say that every time you
PRICE
REDUCED
accomplish a feat _such as shooting a bear ( no
pun intended) or wacking a frog as he jumps up,
you trip a switch. That pulse is sent to a
decoder chip - a 4033 or 4026. What you'll
see is the figure below.
Now in watches, timers, frequency counters,
digital voltmeters, etc., LSI chips are used and
we will get to that in a moment, but the reasons
for using LSI are (as I stated before) design
simplicity, space saving, troubleshooting ease,
and the most important of all - cost savings.
As you'll note in Figure 1, when using one
or more ICs per decade you can simply keep
adding decades by repeating the circuitry over
and over and over again, but multiplexing is a
much better way to handle a lot of digits at one
time.
In a multiplexed display, all of the digits
share one decoder/driver just like in Dragon's
Lair. All of the digits in a multiplexed system
are scanned very quickly in order ( or sequence)
and only one digit is powered up at a time. At
the same instant that that digit is powered up
(by adding+ V to a common anode or GND to
a common cathode unit) the input to the
decoder/ driver is hooked up (via electronic
switching) to the right counter or latch output
for that LED digit.
Multiplexing simplifies the circuitry neces-
sary to drive an LED display by making only
one decoder/driver necessary for the whole
board, whereas in the strict digital system, it's
necessary to have one decoder/driver for each
digit.
Remember, if you have any questions,
answers or ideas for this column, you can send
them to me at Vending International Corp.,
33157 Camino Capistrano- Suite C, San Juan
Capistrano, CA 92675 or call me at
1-800-821-8990, or in California, Alaska or
Hawaii-1-714-661-6808.
Until next month ... "Bear''.
SCORE PUL£;E5
Jl__Jl.__JL
$29. 95 (In Lots of 10)
COMMON CATHObE:
LED DISPLAYS
ZI At-4D Z.2ARE
~02.l, 011 4033 I.CCHIPS.
C.L: C.LOC.K
EN= 1:NABUo
1 to 9 Units - $34.95 each
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All orders shipped UPS/COD.
~N
R~T=RESET
OUT :OUTPUT
A
B
UN I TS OF ONE"
C
D
516-928-6868
COIN UP-DATE
INDUSTRIES, INC.
14 Hulse Road
E. Setauket, NY 11733
E
l'
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TELEPHONE:
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OLIT
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PlJL5E
-----
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