rf - Free and Open Source Software

Add This Simple Decimal
Readout to Your IC Counter
An integrated circuit co unter is a pretty
satisfying project and I can find no primrose
paths in Wes Votipka's article in November
'68 " 73" magazine. One somewhat " un­
American" (whatever that means) aspect of
the counter described is that binary readout
- you must sum the values of the lights
on in each decade t o translate. There is a
fine excuse for this approach if illuminated
readouts are required - in each decade four
lamps and drivers do the job of ten lamps
(nine, if zero is understood), drivers and a
binary to decimal translator. If a diode matrix
is used to translate, forty good, high
back-resistance diodes are needed fo r each
decad e!
Now, my counter is not finished but perhaps
my readout system will be of interest
to others still in the building stage. This low
cost approach gives a true decimal readout.
I use a separate me ter to indicate the output
of each decade - 50 microampere meters
function very well when connected directly
to the outputs of 923 type flip flo ps. The
trick is to pro perly weigh t t he current passed
to the meter by each flip flop of the decade.
The circuit I've used is shown in the figure.
FLIP FLOP FLIP Fl..CP FLIP FLOP FLIP FLOP
"" r- r"
0 , 0 , 0 , 0 ,
'0'
""
'0'
"
'"
eo
,0
..L
C A ~R
Note the binary relationships among the resistors
-- the least significa nt bina ry digit ca n
o nly introduce one half the current supplied
by the next more significant digit and so o n.
Logic levels of individual flip flops will be
different, so equal increments of meter deflec
tion will probably not be observed.
However, the me ter will assume very distinct
positions for each co unt stored in the decade
. Purists ca n trim resistance values to
eq ualize de flection increments I'm satisfied
to let the chips fall where they will and
ma rk the meter scales accordingly.
If there are some misgivings about cost ­
50 microam pere meters are seldom the
cheapest on the list - imports go for about
MAY 1969
$3. Bemg pure Scotch I managed to cut that
by picking up a batch of brand new photographic
light meters from Olson Electronics
in Akron, Ohio, at two for a dollar! These
are 54 microampere movements and, though
not cased , are beautifully made.
I haven't
tackled the mounting problem but it doesn't
appear too difficult. Earl Bryant WA7EYR
San Francisco, Here I Come!
In connection with the hearing on the Miller
suit, I will be in San Francisco from May
26th through the 30th. If any clubs in the
area are interested in having a guest speaker
with a lot to say, please drop a note to me at
73 telling me which night you like. Questions
answered on anything and everything, if you
really want to know what's going on.
Wayne, W2NSD!1
For Your Next Converter
Good old Sears & Roebuck has done it
again. How many times have you battled with
copper flashing material-trying to get it to
take solder, attempting to form it into some
reasonable facsimile of a box or VHF cavity?
If you're tired of burned fingers and torchsoldering,
take heart. Rush down to your
nearest Sears & Roebuck store and invest
about $2. 50 in a roll of their Zinc-Copper
alloy flashing. It c omes I foot wide, and the
rolls are 10 feet long. That's a lot of converters!
It takes solder beautifully. You can lay a
bead with only a gun- no more torches. It
forms easily, and cuts with standard scissors,
or with a paper-cutter. In VHF and UHF applications,
it performs at least as well as co p­
per flashing-and it silver plates easily, to
boot.
Thanks to Jay, K8CJY, for tipping me off
to this great stuff!
Bob Grenell, W8RHR
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67