Introduction:

The toy named Hitting moles with a mallet consists of a board with five holes in its top and a mallet. Each hole contains a single plastic mole and the machinery necessary to move it up and down. Once the game starts, the moles will begin to flash up at random. The object of the game is to smash the individual moles when they flash up directly on the head with the mallet, thereby adding to the player's score. The more quickly this is done the higher the final score will be.

Step 1: Block Diagram

In this block diagram input is obtained from mallet striking
to push button (Switch). This switch is connected to NAND gate along with LED flashier circuit which acts a second input to NAND gate. Here NAND gate is used because counter circuit requires low clock signal for UP-counter.

Both the output of switch and LED flashed should be High to generate a low clock pulse at the output of NAND gate.

Step 2: LED Flasher Circuit

By connecting this diode, D1 between the trigger input and the discharge input, the timing capacitor will now charge up directly through resistor R1 only, as resistor R2 is effectively shorted out by the diode. The capacitor discharges as normal through resistor, R2.

An additional diode, D2 can be connected in series with the discharge resistor, R2 if required to ensure that the timing capacitor will only charge up through D1 and not through the parallel path of R2.

This is because during the charging process diode D2 is connected in reverse bias blocking the flow of current through itself.Now the previous charging time of t1 = 0.693(R1 + R2)C is modified to take account of this new charging circuit and is given as: 0.693(R1 x C).

The duty cycle is therefore given as D = R1/(R1 + R2). Then to generate a duty cycle of less than 50%, resistor R1 needs to be less than resistor R2.Although the previous circuit improves the duty cycle of the output waveform by charging the timing capacitor, C1 through the R1 + D1 combination and then discharging it through the D2 + R2 combination, the problem with this circuit arrangement is that the 555 oscillator circuit uses additional components, i.e. two diodes.

Step 3: Counter Circuit and 7- Segment Display:

·IC 4026 is basically a decade counter (10 States – counts 0 through 9).

Also it has an inbuilt 7 segment display driver which makes interfacing of 7 segment display easily.

·4026 drives only common cathode seven segment displays. As the name indicating a common cathode seven segment display has its cathode shorted and grounded.

·Pin 1 is the Clock input and Pin 2 is the clock inhibit which is used for disabling the clock. It can be used to pause the counting when desired.

·Pin 15 (Master reset pin) helps to reset the counter. Pin 2 and 15 are active high, so we are grounding them to enable the counting process. They should be connected to Vcc for their respective actions.

·Pin 3 is display enable pin which enables the display.

·Pin 5 is the carry output pin which generates a carry each time the count exceeds 9. It is used for extending the counting limit by connecting to the next IC’s clock pin.

·You can use a 555 astable multivibrator as clock input. To know more about the basic working of a 555 timer astable read Astable Multivibrator using 555 timer.

·For 2 digit display digital counter circuit 0 to 99 connect the carry out of the first IC as the clock of 2nd IC as seen below. You can increase the digits as much as you want by repeating the process with more ICs and displays.

·Resistor R1 is used as current limiting resistor. You can vary the brightness of the display by varying the resistance value. But this brightness will not uniform for each digit, Uniform brightness can be attained by connecting individual resistors for each anode segment.

·In this led 7 segment display counter circuit we are using a single digital counter IC (4026) both as counter and 7 segment driver. A common cathode 7 segment display is used here. The IC used here requires only clock pulses for operation.

Step 4: Flow Chart

Conclusion:

In this project we made a toy which helps kids for educational purpose, like how to have hand and eye coordination and learn how to count numbers and have fun.