MM5314N Driven Digital Clock Circuit

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

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.

Source:users.otenet.gr/~athsam/digital_clock_with_MM5314N.htm