Star Tech Journal

22
STAR*TECH JOURNAL/JULY 1983
"The 'Bear' Facts" continued from page 21.
The 7 4C90 has 4 flip-flops, 6 NAND gates and 2 inverters inside. The logic
schematic looks like this:
E to F would be a filtered DC waveform looking like this:
oc----------------
Ain
Ov ---------------- -----
o
As you see, the wave form of the filtered unit is still very unsteady.
A much better rectifier is a full wave bridge. This rectifier is as follows:
a
S R1
a
CLK
a
0
R2
B
CLK
Q
o
a
S R1
R2
0
Your wave form at points A to B without the rest of the circuit will be:
- ~ - -
So, if this is all there is to a Divid-by-Counter, you probably can figure that,
YES!!! you can build Divide-by-Counters using simple JK Flip-flops!
Here's how:
Your wave form at points C to D will be as follows:
OC---------
Ov ____ - ____ - - - - --
Now if your line voltage were to drop, so would your DC voltage, and when
working with logic family circuits, you just can't have that! So, the next step
is to have a regulator in your circuit Since we are talking about 12vdc
circuits (mostly) in this column, let's use a+ 12-volt regulator called a 7812.
The 7812 is capable of having upto I amp run through it which is plenty for
most logic boards. ( 12 watts is a lot of power for a logic board!) What the
regulator does is this: It takes an input of up to 35 vdc and regulates it down to
12vdc.
30
: :
'"1" I
~
0
Ok, now that you've done each step, put them all together and you've got:
~
J!!.
2
In
28.75vac
12vdc
12vdc
a
15
6
a
14
5
K
12
3 CLK
-
Voltage at points A to Breads +30vdc
Voltage at points C to D reads + 12vdc
115vac
0ivid&-by-3
V00
-
CLK
13
I~
10
l!l
a
J
3
K
a CLK
3
-
Divide-by-4s and Ss are similar. So, as you start troubleshooting score
displays and coin/game count circuits, remember that"-they all work
similarly and this is the basic theory behind the operation of such circuits.
o=-----•---- -1..---0-- B
Oivid&-by-2
voo
MotOf
t - - - -...... - - -.....
Your 12vdc regulated power supply!
Ok, I'm sure that most of you have used ohms law and the power laws,
and have learned them fairly well, but for you future technicians that are lost
when I mention these formulae, this is what we are talking about
Ohms law is the most useful formula in all of electronics! It reads as
follows: E (energy or voltage)= I (current)· R(resistance). Another useful
formula is P (power)= I (current)· E (energy or voltage). This last formula
is known as PIE. So, with these two formulae, you can move everything
around using algebra well enough to find every combination. As long as you
have two variables, the third and fourth can be found! Since a lot of you don't
know algebra, I'm going to give you the "PIE DISH". Keep it everywhere
and you'll never get stuck for a formula.
The center quadrant letter represents the value you're hunting and the
formulae on the outside ring equate how you get the answer.
P = Power, I= Current, R = Resistance, E = Energy or Voltage.
Ok, time to get complicated!
We've talked about counters like the4017 and the 74C90. Now let's see
what's making them work!
This month I'm going to be really skimpy on reviews as next month's column
is going to run extremely long.
First, some information has been given to me by Jim Augeri ofSkeeball.
Jim designed the ticket dispensing drive circuit used on Audio Skeeball and
has released some more information to me regarding the fiber problem on the
photo optic switch ticket count circuit
I . National tickets have much cleaner ( fiber dust free) ticket paper than
Globe tickets. If you must use Globe tickets, check them to see which side
most of the fiber dust is on and insert your tickets so that the cleanest side
passes through the optic switch.
2. The Audio Skeeball has a I Ok resistor on the dispenser motor driver
board that can go clear up to 20k to make the optic switch more sensitive.
But, some ticket brands are so thin that wnen the optic switch is made this
sensitive, the optic switch will read nght through the ticket! So, experiment
and feel free to call Skeeball if you have any questions.
Next month I will have a ton of information from Superball Corp. on all
the retrofit units that they have designed that will work on all ball roll-type
games!
Vending International released their first cotton candy vendor units about
eight months ago and the units have been found to have two major weak
spots. Both have corrections and I want anyone who has the unit to be made
aware ofit
The major problem was in the Iron Pot Spinner Assembly. This has been
redesigned and all units can be retrofitted at no charge simply by calling
1-800/821-8990.
The symptoms were: The lower bearing going bad and a short to ground
developing in the AC heater circuit causing the heater band to bum up. The
newly redesigned assembly eliminates both problems.
The second problem was discovered at a Showbiz Pizza Place location
that had people standing twenty deep to buy a cotton candy. When the unit
was run continuously, there was a heat build-up problem in the Iron Pot
Assembly that caused the cotton candy to be shaped improperly.
The correction for this problem is a new EPROM with a 10-second
cooling spin cycle added into each vend. That takes care of the heat problem!
If anyone has any questions concerning this or any non-video unit, give
me a call at 1-800/821-8990.
Well, Peter Gurko of Kiddie Rides U.S.A. has been as tied up as myself this
month, but he did manage to get some info out to me, so once again, here's
Peter ... (P.S. Thanks, Peter!)
Continued on page 25.