Star Tech Journal

20
STAR*TECH JOURNAL/MARCH 1983
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The names of various video games comprise
this issue's word puzzle. Find and encircle
these words that appear below. They run
vertically, horizontally, diagonally and
sometimes backwards.
VIDEO GAMES
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Find these hidden words in the above puzzle:
JOUST
BURGERTIME
PACMAN
QBERT
MILLIPEDE
ZAXXON
PENGO
GALAGA
POPEYE
XEVIOUS
Here is the answer key
to February's puzzle:
PINBALL PLAYFIELD PARTS
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By Mark "Bear'' Attebery, Vending International Corp., San Juan Capistrano, CA
Hello there techs and future techs. The reason I say that is, I've had numerous calls from persons
working as gameroom personnel, doing game repair and board swapping that read Star*Tech
Journal and have asked that I go into more detail on digital logic and how it works. For those
people I will start expounding on basic digital building-block logic. For the more advanced
technicians, I will be finding and bringing basic building-block circuits each month also. But let's
start off with the first future techs lesson.
There are two states in digital logic: "on" and "off'', which is also known as "high" and "low",
or " l " and "0". I will use "l" and "0" as it is easier to write and sometimes I get lazy.
OK, a digital signal can be a solid I, a solid 0, or a pulse sequence that looks like this:
C
M
?4 i~~
D C, E
lJ j~•: C
·' A ::<
C .::::. z
~
C '3
p
;:1
* DIGITAL LOGIC INTRO* 555 TIMER CIRCUITS
* KASCO " DRIVER II" * TICKET DISPENSER FEEDBACK
Now when you have a signal that looks like this on an "0-scope", you should line up the lower side
of the pulse on the reference line of the "0-scope" and measure the voltage from there ...
-------·r-7-------- +10v
___ __j
l _ _ _____ Ov
. .. like that for instance. This is a square wave. Using a logic probe, your high, low, or pulse LED
indicator will light up, but we are going to stick with explaining the logic using oscilloscope
illustrations so that you can see the wave shapes. You also can put a signal other than a square
wave into IC chips and get a different predictable wave form out ( depending on the logic chip). For
you persons who have heard the abbreviations TTL, DTL, MOS, CMOS; these things mean
(respectively) "Transistor Transistor Logic", "Diode Transistor Logic", "Metal Oxide Silicon
( or semi-conductor)", and "Complimentary Metal Oxide Silicon ( or semi-conductor)".
Since a wave form shape can be changed by using a transistor, diode, or capacitor, then the
same changes can be accomplished using IC chips. (Keep this in mind when trying to figure out
why that sound board went out!) What I want you to do if you are really interested in learning how
digital logic works is this: Go down to your local Radio Shack or electronic supply house and
purchase a "proto board" ( your cost will run six to twelve dollars), a cheap + 12-volt power supply
( or if you prefer using TTL I Cs instead of CMOS, a +5-volt power supply) or make one using one
of the schematics (see Figures 1-A and 1-B on page 21).
.. . and the following IC chips: CMOS 4001, 4011, 4069, 4071, 4081, or TTL 7400, 7402,
7404, 7408, 7432. (Remember that if you choose TTL that you can only use a +5-volt power
supply.) You will also need some LEDs, and IC bread board, some 24-gauge solid wire, and that
will be enough. Since this column cannot consume the entire Star* Tech Journal, we will continue
this later.
Now on to a super linear IC that has a million uses. The NE555 timer chip. This chip can be
used to produce a clock pulse, cause frequency tone bursts, and many other functions. Let's disect
this bug. Pin# I is GND, #2 is trigger, #3 is output, #4 is reset, #5 is your control voltage, #6 is
your threshold pin, #7 is the discharge pin, and #8 is VDD. The NE555 IC was the first IC timer
chip and is probably the most widely used, and is extremely easy to use! First, remember your
formula for finding an RC time constant ... for you who have not done this . .. an RC time constant
stands for Resistor/Capacitor time constant and the formula is: (Time= T) T = 1.1 (RI .Cl) So
let's say you want a one second pulse.That means that your resistor value (IM) must negate your
capacitance value to = 1.1 second.
C
= .!.
R
I sec
.
-1 -
= lu or l nucro
meg
So your RC circuit should include I megil resistor and a l mf capacitor.
1.1 = 1.1 second. ((1 x 106) x (1 x 10-6)] = 1.1 second.
Now that you have that down, let's move on ... let's build a one-shot timer.