DLD PROJECTS: DIGITAL STOP WATCH

MADE BY:

Muhammad Inamullah (CEO)

Muhammad Mussab Bin Aamer (Wear house Manager)

Muhammad Shahab Ahmad (Marketing Manager)

Digital STOPWATCH:

Components:

IC 4026 - 4
555 timer IC -1
Common Cathode 7 Segment Display -4
150 Ohm -1
100K resistor -1
33K resistor -1
56K resistor -1
10uF capacitor -1
On/off switch -1
Push button -1
Breadboard -1
9 Volt Battery -1
Battery Connector -1
LED -1
Voltage Regulator 7805 -1
Connecting wires

Digital Stopwatch Circuit Diagram and Explanation:

In this circuit we have used a 555 timer IC based a stable multi-vibrator which is for creating 1-second delay. And two common cathode seven segment decoder IC’s namely CD4033. The output of a stable multi-vibrator is directly applied to seven segment decoder IC’s (U4) Clock pin (1) and carry output pin(5) of U4 IC is directly connected to the clock pin (1) of the second seven segment decoder(U3). And two seven segments are connected with this decoder (U3 and U4). Its connections are shown in the stopwatch circuit diagram given below. One push button is used to stop /start the stopwatch and one push button is used to reset the stopwatch. A 5-volt voltage regulator is used for providing 5 volts to the whole circuit. And a 9-volt battery is used for powering the circuit. Rest of connections are shown in the circuit diagram.

Working:

In this stopwatch circuit, we have generated one-second delay by using 555 timers based astable multi-vibrator. By using some calculation we can easily generate a one-second delay. In a stable multi-vibrator, there are two resistors and one capacitor is responsible for delay by charging or discharging the capacitor through resistors.

We can set the 555 to work at the desired frequency by selecting the right combination of resistances & capacitance.

Frequency = 1.44 / {(R1 + 2R2) * C1}

Also, 555 can produce waves with duty cycle else than the 50 % cycle.

Duty Cycle = (R1 + R2) * 100/ (R1 + 2R2)
where duty cycle = Ratio of the time period when the output is 1 to the time period when the output is 0.

In this project, we have selects R1 is 1K, R2 is a 100K variable resistor and C1 is 10uF. [Also check: 1 minute timer circuit]

As a stable multi-vibrator generates one second's delay, this delay is oscillations or pulse of 0 and 1. So we will use this pulse for triggering the seven segment decoder then seven segment decoder changes the digit number with the one second of time period.

When we ON the stopwatch (by start/stop button) it starts counting from zero and if we turned OFF the same button then counting is stop or pause until again turned ON the same button or press reset button.

There are four seven segments, so this stopwatch the circuit can count 00-59 seconds to 00-59 minutes time. Two seven segments are for seconds and the other two seven segments are for minutes.

Components descriptions:

IC 4026:

The IC CD4026 is an IC which can perform the function of both a counter as well a 7-segment Driver. One single IC can be used to count from zero (0) to nine (9) directly on a Common Cathode type 7-segment display. The count can be increased by simply giving a high clock pulse; also more than one digit (0-9) can be created by cascading more than one CD4026 IC. So if you have a 7-segment (CC) display on which you have to display numbers that are being counted based on some condition then this IC will be a perfect choice.

How to use a CD4026 IC

The IC can work from 3V to 15V, but normally powered with +5V to the Vdd/Vcc pin and the Ground/Vss the pin is connected to ground. We have 7 output pins naming from Out A to Out G which is directly connected to the 7-segment display. The clock inhibits pin (pin 2) has to be held low (ground/0V) so that the clock signals can be sent to the IC also the Enable Input pin (pin 3) should be made high (+5V) so that the output pins (Out A to G) can be made active.

The 7-segment pins will increment the count by one number each time when the clock pin (pin 1) is made high. This clock source can either be obtained from a 555 IC or any other digital IC which is TTL compatible. They simply have to generate a pulse of low voltage 0V and high voltage 5V. In the circuit below I have used a clock source of 1Hz to increment the count. So the number will get incremented for every (T=1/F) 1 second.

The Reset pin (pin 15) is used to reset the count back to zero when made high. There are three other output pins (pin 5,4,14) which will be used only when the IC needs to be cascaded. The pin Carryover (CO – pin 5) will stay high by default, but when the count reaches “9” it will give a small pulse and count will continue from “0” again. This small pulse can be used to drive the clock pin of a cascaded IC to display more than one digit. The Direct Enable output (DEO) pin will always stay high, to enable any cascaded IC, if available. The Ungated C segment pin (pin 14) is used for any division operation; this pin will stay high by default and will go low when the count reaches “2”.

Datasheet:

CD4026 Pin Configuration

*Pin Number*	*Pen Name*	*Description*
1	Clock (CLK)	The counting happens when this clock pulse goes high, this pin is normally connected to 555 timer or other uC to produce a pulse
2	Clock Inhibit (INH)	Connected to the Ground (low) of the circuit, to enable clock pin
3	Enable Input (DEI)	This the pin is connected to +5V (high) to enable the output pins (Out A to Out G)
4	Enable Output (DEO)	This is an output which always stays high, this pin will be only if more than one CD4026 IC is used (cascaded)
5	Divide by 10 (CO)	This is the carryover output pin; it produces a pulse after counting till 9. This the pin will be only if more than one CD4026 IC is used (cascaded)
6,7,9,10,11,12,13	Out A,B,C,D,E, F,G	These are the decoded output pins which should be connected to 7-Segment display.
8	Ground	The the ground pin should be connected to the ground of the circuit
14	Not 2 out (UCS)	This is Ungated C segment pin. This is an output pin which will be rarely used when division is required.
15	Reset	This input pin when made high (+5V) will reset the count to 0.
16	Vcc	This pin powers the IC, typically +5V is used.

Features:

· Counter for 7-Segment display

· Can drive a common cathode 7-Segment display directly

· Easy to interface with a timer or micron rollers (TTL compatible)

· Can be easily cascaded with more IC to display higher range of number

· Maximum Clock Frequency: 6Mhz

· Available in 16-pin PDIP, GDIP, PDSO packages

Clock Source (multivibrator):

Individual Sequential Logic circuits can be used to build more complex circuits such as Counters, Shift Registers, Latches or Memories, etc, but for these types of circuits to operate in a "Sequential" way, they require the addition of a clock pulse or timing signal to cause them to change their state. Clock pulses are generally square-shaped waves that are produced by a single pulse generator circuit such as a Multivibrator which oscillates between a "HIGH" and a "LOW" state and generally has an even 50% duty cycle, that is it has a 50% "ON" time and a 50% "OFF" time. Sequential logic circuits that use the clock signal for synchronization may also change their state on either the rising or falling edge, or both of the actual clock signal. There are basically three types of pulse generation circuits depending on the number of stable states,

• Astable - has NO stable states but switches continuously between two states this action produces a train of square wave pulses at a fixed frequency.

• Monostable - has only ONE stable state and if triggered externally, it returns back to its first stable state.

• Bistable - has TWO stable states that produce a single pulse either positive or negative in value.

IC N555 Timer:

Pin diagram and description:

*Pin*	*Name*	*Purpose*
1	GND	The ground reference voltage, low level (0 V)
2	TRIG	The OUT pin goes high and a timing interval starts when this input falls below 1/2 of CTRL voltage (which is typically 1/3 Vcc, CTRL being 2/3 Vcc by default if CTRL is left open). In other words, OUT is high as long as the trigger low. The output of the timer totally depends upon the amplitude of the external trigger voltage applied to this pin.
3	OUT	This output is driven to approximately 1.7 V below +Vcc, or to GND.
4	RESET	A timing interval may be reset by driving this input to GND, but the timing does not begin again until RESET rises above approximately 0.7 volts. Overrides TRIG which overrides threshold.
5	CTRL	Provides “control” access to the internal voltage divider (by default, 2/3 Vcc).
6	THR	The timing (OUT high) interval ends when the voltage at threshold is greater than that at CTRL (2/3 Vcc if CTRL is open).
7	DIS	Open collector output which may discharge a capacitor between intervals. In phase with output.
8	Vcc	Positive supply voltage, which is usually between 3 and 15 V depending on the variation.

Some important features of the 555 timer:

555 timer is used in almost every electronic circuit today. For a 555 timer working as a flip flop or as a multi-vibrator, it has a particular set of configurations. Some of the major features of the 555 timers would be,

· It operates from a wide range of power ranging from +5 Volts to +18 Volts supply voltage.

· Sinking or sourcing 200 mA of load current.

· The external components should be selected properly so that the timing intervals can be made into several minutes along with the frequencies exceeding several hundred kilohertz.

· The output of a 555 timer can drive a transistor-transistor logic (TTL) due to its high current output.

· It has a temperature stability of 50 parts per million (ppm) per degree Celsius change in temperature which is equivalent to 0.005 %/ °C.

· The duty cycle of the timer is adjustable.

· Also, the maximum power dissipation per package is 600 mW and its trigger and reset inputs has logic compatibility.