This was one of my projects constructed during my college years. It is a digital chess game clock which can be operated at 9:00 minutes blitz game with 2 players competing in a game of chess. Time is accommodated for each player for each move they make. Several buttons and switches are used for setting the time, start and stop, and for reset. Each player touches a switch to stop his time and starts the opponent’s time. The game will end when the time will expire and it will determine the winner of the chess game.

The Plan:

My designs were based on a standard chess game clock except for the time setting. I chose a time setting which is intended for amateurs in chess games. My design were composed of two timers with set buttons for seconds and switch button for players. A 1 Hz clock pulse oscillator is also implemented in the timer for countdown purposes.

SWITCH and RESET BUTTONS

The set buttons are connected to pin 14 (CLK) and then to the 74LS08 on their pin 3. Pins 1 and 2 of the same IC then is connected to pin 7 (Q3) of 74LS190 which is the flip flop output.

The on/off switch which is a single pole – dual throw switch is connected to pin 14 (CLK) of the 74LS190 on the upper side circuit.

The dual pole – dual throw switch is connected to the on/off switch. The upper pole of the dual pole – dual throw switch is connected to the 1 Hz oscillator. The lower pole is connected to the 1 Hz oscillator and to pin 14 (CLK) of the lower side circuit.

2N222 transistors are also implemented so that the count for the set buttons will be descending to 0. The 2N222 transistor is connected to pin 11 (PL) Parallel load control input, and the base and emitter is connected to pin 7(Q3) and GND.

DISPLAY

The display used in the design is a common cathode BCD 7-segment decoder. I only used 3 digits for the dual timer. 470K resistors were connected to each pin of the decoder so that it will prevent overdrive of the LEDs. The 7 segment decoder is then connected to 74LS48 IC to their pins 9 to 14 which are the outputs for the display. The BCDA inputs which are the pins 1, 2, 6 and 7 are then connected to the flip flop outputs from the 74LS190 pins 3, 2, 6 and 7. The first IC of 74LS190 the parallel inputs pin 15, 1, 10 and 9 identified. Pins 1 and 9 were connected to Vcc=5V and pins 15 and 10 were connected to ground. The display in in the 7 segment decoder will now be on number 9. Next the second IC of 74LS190 parallel inputs were connected to display a certain number 5. Pins 15 and 10 were connected to Vcc=5V and pins 1 and 9 were connected to ground. The reading then displays the number 5.

THE OSCILLATOR

Explain here

A crystal oscillator is an electronic circuit that uses the mechanical resonance of a vibrating crystal of piezoelectric material to create an electrical signal with a very precise frequency. This frequency is commonly used to keep track of time (as in quartz wristwatches), to provide a stable clock signal for digital integrated circuits, and to stabilize frequencies for radio transmitters. The crystal oscillator circuit sustains oscillation by taking a voltage signal from the quartz resonator, amplifying it, and feeding it back to the resonator. The rate of expansion and contraction of the quartz is the resonant frequency, and is determined by the cut and size of the crystal.

Resonance modes

A quartz crystal provides both series and parallel resonance. The series resonance is a few kilohertz lower than the parallel one. Crystals below 30 MHz are generally operated between series and parallel resonance, which means that the crystal appears as an inductive reactance in operation. Any additional circuit capacitance will thus pull the frequency down. For a parallel resonance crystal to operate at its specified frequency, the electronic circuit has to provide a total parallel capacitance as specified by the crystal manufacturer.

Crystals above 30 MHz (up to >200 MHz) are generally operated at series resonance where the impedance appears at its minimum and equal to the series resistance. For these crystals the series resistance is specified (<100 Ω) instead of the parallel capacitance. To reach higher frequencies, a crystal can be made to vibrate at one of its overtone modes, which occur near multiples of the fundamental resonant frequency. Only odd numbered overtones are used. Such a crystal is referred to as a 3rd, 5th, or even 7th overtone crystal. To accomplish this, the oscillator circuit usually includes additional LC circuits to select the desired overtone.