ground ONLY to the active-input display. Even
though a counter is outputting the data for the
zero in the reset condition, the lack of a ground
through FET T1 to the display did not show it
[preserving battery energy].
With the next input pulse count (number 1),
the FET is turned on to provide a ground to
display the intended number 1. Note here that
the number 0 is not stored within the counter
on a reset if it’s disabling the DE input at that
time with a low input.
If the display enable is returned to a high, it
would then output and display the number 0 on
the next input clock pulse and not the intended
number 1. Using FETs allows for the DE inputs
to be constantly enabled and prevents this
And a One, and a Two ...
Notice that regardless of which input device is
activated, all counters receive and store the exact same
input pulses, and they are counted and stored within
each of them as the same value. For example, if DV1
receives the first input, a number 1 is shown on its
associated display, but a count of 1 is also stored within
all of the other counters. However, only the DV# active
input will display its immediate counter-input order
The very next device input will display a number 2
on its associated counter, even though all of the other
counters have a 2 stored within them (but not displayed).
Once a device input is made to its respective counter,
the input order number is displayed but the chip enable
pin 2 input is disabled, and prohibits any further inputs
while continually displaying its initial input number.
Diodes D3 and D4 prevent other high output pulses
to the clock inputs from being present on the AND gate
output pins. As many as five boards can be ganged
together by using jumper wires between each two-display
boards, or by using two of the available four-display
boards for eight display outputs.
What Else Ya Got?
Another use for this project might be to monitor (at
the sound of a bell or light activation) the reaction input
speed of pitching a ball at switch-activated targets among
competing pitchers, or perhaps as an associated-type
table game item.
To store this project, simply press the reset button to
shut off all the displays and put it away. No negotiable
power is consumed during this time. I recommend using
a nine volt battery.
Putting It All Together
I constructed the project with four red displays
[two boards jumpered together] in a 6” x 3” x 2” plastic
enclosure. You can use any color display indicated in the
Parts List; blue is the most expensive but yet the most
visible. I recommend the use of a circuit board assembly.
I had no problems whatsoever constructing this
project. I used jumpers between two two-input/two-display boards as indicated in the schematic. I combined
two of these latter boards together for a single four-input/four-display board. If you use two two-display
boards, I recommend that you solder in the .100 male
headers [snapped off by two’s] to easily place in each of
the jumper locations, and use them to wire wrap
between the board jumper connections.
As mentioned earlier, I do have four-input board
layouts available, as well as the files for either board for
those that want them. Again, simply email me and I will
send the files for your use.
As a construction hint, solder all the resistors and
March 2014 31
■ Two-input circuit board layout.
■ A look at the monitor.