TV and video games have become very popular, both with children and grown-ups. These games provide good recreation as the animated figures make the player feel as if he is actually playing with another human being.
The circuit described here is the basic circuit for all electronic games of this kind. Once you assemble it only a little imagination is required to make other games.
In this circuit, costly and not easily available LCD panel is avoided and only LEDs are used for display- For low static power dissipation, fully CMOS ICs art used.
The game and how to play it
Like all electronic video games this one also tests one’s reflex action, i.e. the speed with which one reacts. The quicker one acts, the faster one scores over the opponent.
Nine switches are used in 3×3 matrix form. In the same way, nine LEDs arc fixed in identical places (Fig. 7). These LEDs arc lit one by one at random. ‘Hie player has to press the switch of identical place where the LED glows. If the switch is pressed before the LED goes off the player scores one point.
Fig. 1 shows the block diagram of the circuit. The pulse generator produces positive clock pulses to run the random number generator and for the proper operation of debouncer and foul play checker circuit.
Ten outputs of the random number generator go high one by one on every positive clock pulse. The outputs are buffered before connection to the LEDs of the display circuit for good illumination. The triggering circuit contains nine switches for shooting (triggering) the number in this game. The circuit may have only one or a few switches in other games, A debouncer and a foul play checker circuit prevents the player from using unfair means.lt also shapes edges of the trigger pulses.
One output is taken from debouncer circuit to the counter/driver circuit for the scoreboard.
Clock pulse generator circuit
Let us first see the requisite of the clock pulses. It takes as some time (fraction of a second) to react to an action. The reaction time varies from individual to individual. If a period of one second (that is LED glow period) is allowed as reaction time, the player would surely shoot all the randomly generated numbers. If it is 0.5 second then the player has to show some skill. A challenge begins when the set time period is 0.3 seconds. With this setting, one has to press three switches (of course the correct one) every second. Below 0.3 seconds more swiftness is required to score more.
So, for our game, a maximum variable period of one second between successive clock pulses is required. Usually. timer ICs, inverters, NAND, NOR or schmitt trigger NAND gates are employed to produce clock pulses. But here JK type flip-flop is used because of the foul play checker circuit. These being two flip-flops in a single chip. So the unused flip-flop is wired as an as* tabic multivibrator.
CMOS ICs for almost all their operations such as setting, resetting, changing states require positive going clock pulses. The output of CMOS IC2 is high and the LCD stays lit until the arrival of the next clock pulse. The player has to shoot the number by pressing the correct switch before the beginning of the next clock pulse. Hence the period between the two consecutive pulses should be variable.
Fig. 2 shows the circuit diagram of number shooting game. The clock pulse generator circuit is wired around half of CD4027 (IC1) which is a dual JK type flip-flop. Suppose IC1 ’s output Q (pin 15) is high and 0 (pin 14) is low, then capacitor Cl charges through VRl. When the voltage across Cl crosses half of the power supply voltage, it resets the output 0 to low and Cl discharges through D1. Now Q being high and 0 low. C2 charges through VR2 and Rl. When C2 reaches half of the power supply voltage it again sets Q to high and 0 to low. Here C2 discharges through D2. Thus the cycle repeats. VR2 sets the low period and clock pulses are taken from output Q,
Random number generator, trigger, buffer, and display circuit
CD4017 (IC2), a decade counter/ divider, is used for random number generation. Actually this IC does not produce any number. But its ten outputs go high one by one for every positive going clock pulse and each output I remains high until the next clock pulse I comes. So only one output remains high at a time.
The first nine outputs Qo through | Q8(and all ten outputs in other games) are buffered by CD4050 (IC3, IC4) and connected randomly to the nine LEDs placed and numbered in order. Thus random position here means random number generation.
In our case the numbers generated i are 1,9,83,4,2,6,7 and 5, and the cycle repeats. One can connect the outputs to LEDs (after buffering) in any order.
One terminal of the triggering switches are connected to the outputs of IC2 and the common terminal is taken to the debouncer circuit (pin 3 of IC1).
The 100k resistors connected to reset terminal (pin 15) and chip enable (pin 13)of IC2 connect these pins to ground fa this game. These pins can be used in other games.
‘ The LED current limiting resistor 9.6 of lk is chosen to get optimum flluminance of LEDs. Its value may be Increased or decreased. But do not try to approach the maximum current limit
LEDs or IC4050.
Debouncer and foul play checker circuit
All mechanical switches when activated bounce before coming to the steady state and produce spurious pulses that result in erratic operation of the circuit.
One may try foul play by pressing a switch before the identically positioned LED lits or pressing the switch repeatedly in an effort to score more points.
So for a fool-proof system, the circuit requirements are:
(a) The spurious pulses must be ignored.
(b) Only one point must be given even if one triggers several times during the LED’s lit period.
(c) The triggering before any LED lits must be ignored.
All these conditions are easily met by the JK flip-flop. Once the clock pin 3 of 1C 4027 is triggered positively its output at pin 1 goes high and activates the counter. At the same time the output at pin 2 (which is connected to pin 6)goes low. As pin 5 input is also low the IC is inhibited and ignores further pulses (requirements a and b).
The output changes the stale only on positive going pulse. Suppose one keeps pressing the switch and waits for the respective LED to lit. When any output of IC2 is high the clock input of IC 1 (pin 3) gets high as the corresponding switch is kept pressed. But Q output of IC1 will not change its slate. Because the reset pin (pin 4) is also receiving positive clock pulses from the clock pulse generator, it overrides all output at pin 1 to low state.
Though the reset pin goes low when the switch is kept pressed, the output will not go high as only the positive going clock pulse will change the output, i.e triggering after the LED is on.
Counter and scoreboard
Any CMOS compatible counter and display may be used, but here (CD 4033) a decade counter/seven-segmet driver and common-cathode LED display is used. The 100k resistor connected at lamp test terminal (pin 14) is useful for checking the display. When this terminal is high the display should light up all segments. Switch S10 is used for resetting the counter.
Sound effect generator
When a successful shooting is announced by a sound, it is more exciting. Sound generation can be obtained if the output of debouncer,IK flip-flop is buffered before being connected to the piezo buzzer. It may also be connected to the gun sound generator or any other circuit like it.
The soldering sides of the PCBs and the component layouts are shown in Figs 3. 4, 5 and 6. All measures have been taken to make the design flexible and to suit all similar games. For this reason the reset and clock enable pins of IC2 are grounded through 100k resistors. Besides, two PCBs are being recommended, one for the control circuit (which should remain common) and the other for display and switches.
As the PClis are small they can be fixed easily on available plastic cabinets, You will be surprised to see that many games can be played simultaneously. So wait until you decide on the number of games you prefer. Then choose the cabinet.
Nine LEDs and switches are arranged in a rectangular shape. However, all the ten outputs (including output Q9 of IC’2) can be used to get any shape. And don’t forget that the arrangement of LEDs and switches must be identical.
LEDs of any shape and colour can be used but the flat type will give a better look. For triggering, switches of any type, from membrane to simple push-to-on or even switch pad of a worn-out calculator, would serve the purpose.