Seven Segment Digital Clock Circuit Using MM5314
Overview
The circuit has been designed to create a digital
clock using a single IC MM5314N with all the
functions provided in the operation.
Terminology
- MM5314
– a monolithic MOS integrated circuit that utilizes P-channel low
threshold, enhancement mode and ion planted, depletion mode devices which
has features such as internal multiplex oscillator, fast and slow set
controls, single power supply, 7-segment outputs, leading zero blanking,
operating at 50 Hz or 60 Hz, and 12 or 24 hour display format
- 7
Segment LED – is a form of electronic display device for
displaying decimal numerals that is an alternative to the more complex
dot-matrix displays also known as seven-segment indicator
Circuit Explanation
A digital clock is a type of
clock in which the time is displayed in a numerical form being associated with
electronic devices. It uses a digital display rather than moving hands. The
basis of the circuit design evolves in a single MOS IC MM5314N.
Other necessary circuits are operated through the MM5314 IC
which works together with six common anode 7-segment displays. The multisegment
LED common anode configuration reduces the number of wires between the LED
modules where all positive ends are connected together. In practical design,
the longest pin of the LED is the positive or the anode part.
The 7-segment displays are driven by thirteen transistors
consisting of BC550 and BC560. The timing of
the circuit is determined by the frequency of the network with a value of 50
Hz, which imposes the simplest solution. To maintain a stable output frequency, a crystal oscillator may be used. It
uses a quartz crystal to produce fixed frequency oscillations where accuracy
and stability are the primary considerations. It uses the mechanical resonance
of a vibrating crystal to produce a very precise frequency from the creation of
an electrical signal.
The six displays of 7-segment common anode
provide the output for the time. LEDs DS1 and DS2 represent the Hour, LEDs DS3
and DS4 represent the Minutes, and LEDs DS5 and DS6 represent the
Seconds. The collector of transistors Q8 to Q13 powers the common anode
of each display. Each display consists of individual LEDs a, b, c, d, e, f,
& g, are linked in parallel combination, which are then driven by the
transistors Q1 to Q7. This type of connection creates a multiplexing system
with a frequency of 1 KHz that is controlled by the RC circuit R3 and C3. The
power supply contains the typical circuit having a bridge rectifier across the
secondary coil with a parallel capacitor across the bridge. The resistor R2 and
capacitors C2 to C5 handles the separation and limiting of voltage to protect
the integrated circuit from surge and peak voltages.
The rectified vibrations in pin 16 are limited by
the diode D1 while resistors R18 to R24 are limiting the excess current from
the LED. The use of switch S1, if put in position 1, is to adjust the clock to
the required time and display. It will remain open unless it is switched to the
other position which causes the display to be in a fixed value and save the
settings, resuming the operation of the clock. In this scenario, the clock may
be placed with a tolerable distance to avoid the effect of light from the LED
display. Switch S2 on the other hand is responsible for adjusting the clock to
operate on a 12-hour or 24-hour basis by changing the positions of the
contacts. The adjustments of seconds are made possible when switch S3 is in
position 1. The setting for the seconds is saved when the contact is changed to
position 2. During an interruption in the operation of the clock, switches S3,
S4, and S5 can be used for alterations. These are push-to-make switches which
return to its normally open or OFF position upon releasing the button, like the
standard doorbell switch.
The frequency of the main voltage around 50 Hz or
60 Hz is fed into pin 11 which is connected to pin 2 if the main voltage is 110
VAC at 60 Hz. Otherwise, pin 11 will not be connected anywhere if the main
voltage is 220 VAC at 50 Hz. Pin 16 handles the incoming 50 Hz or 60 Hz at the
input with the sample from the main voltage. The counter circuits are triggered
by the sample function which becomes the adjustment of time. Having 110 V
causes the pin 11 to connect Vss at pin 2 while having a 220 V nulls the
function of pin 11.
Part List
|
R1=
100Kohms
R2= 47Kohms
R3= 100Kohms
R4.....10= 2.2Kohms
R11.....17= 10Kohms
R18.....24-25-26= 220 ohms 0W5
R25-26=1.2Kohms 0W5
|
C1= 2200uF
25V
C2= 100uF 25V
C3= 18nF 100V polyester
C4-5= 10nF ceramic OR polyester
Q1....7= BC550
Q8....13= BC560
IC1= MM5314N
|
D1= 1N4148
GR1= 4X1N4002
S1...3= 1X2 mini switch
S4...6= Push Button normal open
T1= 220V AC/12V 1A
DS1....DS7= 7 Seg. Disp. Common Anode
|
Application
Digital clocks are widely used
as desk clocks, interval timers, industrial clocks, or automobile clocks. They
can also be utilized in cell phones, computers, microwave ovens, televisions,
and radios, since digital clocks are inexpensive and very small devices, which
make them more popular in the designs. The LED digital clocks are also used as
digital electronic time zone displays used in governments and companies with
more than one office across the country or around the world. Schools,
universities, and hospitals are using wireless clocks as the desired method for
providing synchronized clocks without the need to lay sync wire.
