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Master Clock    

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Features

Master clock Synchronized to the DCF77 "Atomic" Clock in Frankfurt

·        1” High Brightness 7 segments display of Hours, Minutes and Seconds

·        24 Hour transistor switched pulse output with diode protection

·        1 Hour transistor switched pulse output with diode protection

·        30 Second transistor switched pulse output with diode protection

·        Seconds reset and pause for precise clock setting

·        30 Second pulse can be synchronised with clock display at 00 & 30 seconds

·        Hourly Chime with switch for silent night time running

The Master clock can run any number of slaves by adding extra relays/transistors

Master Clock video in HD

Complete Master Clock System Master & Slave Dials

Master Clock Construction Details
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Components 1.5” 7 segment displays are driven and controlled by CMOS ICs. The time is kept by a 32.768KHz Quartz Crystal.   Components are mounted on Tripad Board and fitted in an Oak case.

Operation

Time Display Diagram 1

The circuit uses 4026B Decade counter, decoder and display driver ICs to drive the 7 segment displays and decode the time.

The 1 second pulse from (diagram 2) is connected to the input pin 1 of  IC11. This IC counts from 1-0 and displays the seconds units via the LED display. When the count reaches 0 on the 10^th pulse the IC resets and outputs a pulse to IC9 input pin 1. This advances the seconds tens display by 1. Every 10 seconds IC9 is stepped by 1 until the count reaches 60 seconds or 6 pulses to IC9. IC9 & 11 are reset by IC2d and IC12a. This reset also steps the Minute Units by 1 via the Set Secs switch not operated, IC7a and IC7b to IC8 input pin1.

The minute unit segment is stepped every minute and as per the seconds unit it will be reset at 0 and pulse the minute tens segment. Again when the minutes tens segment steps to 6 (60 minutes have elapsed)  the minutes are reset IC6 & 8 via IC2 b&c. A pulse is also sent to the hours display via IC3 b&c to IC5 pin1.

The hours units are therefore pulsed every hour. When the hours units IC5 reaches 0 it  pulses the hours tens IC1. This continues until the hours units reaches 4 and the hours tens reaches 2 (24:00). The logic ICs IC2a & IC4a then reset IC1 & IC5.

Clock Setting

Seconds

Seconds can be reset by operating the reset button SW3. This applies +ve to the reset pins of IC 9 & 11 to reset the seconds display.

The seconds can also be stopped by operating SW4 this resets the divide by 2 counter. The seconds pulse is stopped as long as SW4 is held.

Pulses  Diagram 1

30 second sync pulse

This pulse is produced every 60 seconds from the reset pulse from  IC2d and IC12a. This is used to synchronise the display with a 30 second slave clock.

1 Hour Pulse

This is produced by the reset pulse from IC2b & IC2c. This is fed out externally via IC6c & IC6d and the output transistor TR2.

24 Hour Pulse

This is produced by the reset pulse from IC2a & IC4a. This pulse is used to synchronise the hourly chime at midnight. 

This is fed out externally via IC12c & IC12d and the output transistor TR3.

1 Second Pulse Diagram 2

The 1 second pulse is derived from a 4060 14 stage binary ripple counter IC with a built in oscillator. The oscillator is driven by a 32.768Khz Quartz crystal.

The 4060 divides the 32.768Khz by 2 to the power of 14. This gives a 2Hz output from this IC at pin 3. The 2Hz pulses are then fed into IC5 a Binary counter. The output from pin 12 (divide by 2) is used as a 1 second pulse.

30 Second Pulse Diagram 2

The 1 second pulse is fed into IC1 a 4017 decade counter/divider IC. Every 10 seconds IC1 pulses IC2. When IC2 receives 3 pulses (every 30 seconds) the IC is reset and a pulse is sent out on pin 7.

30 Second Pulse Synchronisation Diagram 2

The 30 second pulse can be synchronised with the display by operating SW1 until the seconds read 00. SW1 should then be released. When operated SW1 connects the reset pins of IC1 & 2 to the 60 sec pulse. This pulse is produced when the seconds display reaches 60 so IC 1 & 2 are therefore reset as the display reaches 60 and are then in perfect sync.

Output Pulses  Diagram 2

All pulses that drive external devices go through logic ICs configured as monostables. These monstable control the shape and timing of the pulses. The monostables then drive medium power transistors with diode protection so they can drive relays etc.

The 30 second pulse output can drive 1 30second clock. You can connect as many as you want by using external relays or power transistors.

30 Seconds Slave Clock Control Diagram 2

The slave clocks are controlled by SW5. In its normal position SW5 connects the 30 second pulse to the drive transistors so the clocks pulse as normal. SW5a lights the Gn LED “30sec clocks ON”. Note this LED lights rather than the RED led due to the extra voltage drop across the RED led and diode. The “30 sec” LED will also pulse to show the cct is working.

With SW5 set to “Retard” the 30 second pulse is disconnected from the drive transistors and the slave clocks stop. Note slave clocks cannot be stepped backwards. To set clocks for winter time the clocks are stopped for 1 hour. SW5a disconnects the Green “30sec clocks ON” LED and allows the Red “Retard” LED to light. Note on operating SW5 the clocks will step forward 1 pulse or 30seconds. This is useful for fine setting the slave clocks.

With SW5 set to “Advance” the slave clocks are advanced every second. SW5 connects the 1 second pulse to the drive transistors. The “30 sec” LED will light every second to show the slave clocks are being advanced.

Diagram 2

1 Second & 30 Second Pulse Generator with drive circuits

Master clock showing display board and external connections on main board below.

The quartz crystal trimmer capacitor is just visible above the white label bottom left.

Three silver toggle switches for 30sec synchronisation, advance & retard of 30sec slaves and chime on & off can

be seen above the white label to the bottom right.

The labels for the display are on a 2nd sheet of glass spaced 1mm from the front glass. Dry transfers were used for the lettering.

Hourly Chime Circuit   The chime circuit uses 2 CMOS 4516 Binary Up Down Counters to count then pulse out the hourly chime. The chime pulses drive a miniature relay with a copper wire soldered to the armature as the hammer. The bell is from an old telephone but any bell or gong can be used.   Hourly Chime Diagram 3   Operation Diagram 3 The 1 hour pulse is fed into the chime setting circuit at IC7c and out through IC7b. From IC7b the pulse is fed to IC5a one of a pair of D Type Flip Flops CMOS 4013. These flip flops are configured as Monostables. The not Q output is fed to IC5b the other Monostable pair. The Q output is fed to IC1 4516 configured to count up. The Q output is fed to IC2 4516 configured to count down.  Note there is a delay between the Q outputs on IC5a and IC5b see below. The Q output from IC5a steps IC1 up by 1 every hour pulse. This count is sent to IC2 via its BCD inputs from IC1. IC2 is now set at the count from IC1.   When the delayed Q output from IC5b is received at IC2 it will start to count down to 0. The delay allows IC1 to count up and set IC2 before IC2 counts down to 0. Chime count down is monitored by LEDs 6,7,8 & 9 and is displayed in BCD format.   The chime rate is set to 1 second and is fed from the 1 second pulse to IC4b & c to the drive transistor. The 1 second pulse is also fed back to the input of IC2 via inverter IC3d to count this IC down. When IC2 has counted down the 1 second feed to the drive transistor is turned off using logic via the inverter IC3b.   Although the Master clock displays in 24 hour format the chime will sound in 12 hour format. IC3a, IC3b & IC4a are logic gates that detect the 13th hourly pulse and then set IC1 back to 1.   Chime Setting Diagram 3 When setting up the clock the chime has to be synchronised with the display. IC7a, b, c & d are set up as a noiseless switch and by pressing and releasing SW1 the chime is advanced by 1. The chime will sound out each time SW1 is depressed but there is no need to wait for this just keep pressing SW1 until the BCD LED display shows the same hour as the clock. The chime is now set and will chime out as the main clock display hits the hour.   To ensure the chime remains synchronised with the display the 24 hour pulse is used to synchronise the chime at midnight. IC6a & b again configured as monstables are used for this purpose.   Chime Setting Diagram 3 cont. At midnight the 24 hour pulse is fed to the monostable IC6a. The Q output is fed to the D input of IC6b on the 1 second clock pulse. The Q output from IC6b is then used to reset IC1 again on the 1 or 2 sec second clock pulse. IC1 is now reset with enough delay to send BCD 12 to IC2 and also IC2 is allowed to pulse out 12 to the chime transistor. Chime  Control Diagram 3 The chime can be turned on and off by SW2. When SW2 is on it simply connects the chime relay to the supply rail. When SW2 is off the chime relay is disconnected and the chime off LED is connected instead to the supply rail.
Chime board mounted on the top of the master clock. Note tri-pad board has been sprayed green before mounting the components and wiring.
Chime Options
Chime via a min relay and telephone bell. This has a nice sound as is very compact but is not very loud.	Chime via a 4" longcase clock bell and 30sec clock movement. This option gives out a very loud chime but takes up a lot of space. I have fitted it into the case of my longcase clock and disabled the longcase clock chime.
The electromechanical bell chime installed in the base of my Longcase clock.     Wiring Due to the tight space on the boards I have used 0.4mm wire for the connections between components. I have used multiple Batt and Eth runs to spread the load on these small conductors. Wiring to slaves will depend on the number and distances involved.     I have used 4 boards for this project due to the limited space in the case. They are as follows.   Display Board I used the following  connections from the display board .           Mainboard This contains the display ICs and logic and is made using Tripad board. Mainboard rear. Oscillator Board front and back The oscillator board is mounted away from the main board in a position that is easy to reach so the oscillator can be adjusted to 32.768KHz.   The oscillator is effected by temperature but should be able to keep time well within a second a week at room temperature.   Quartz crystal accuracy  against temperatue graph for standard and temperature compensated types If the clock is used in building with wide temperature variations then a temperature compensated crystal should be used. In the graph above you can see the temperature compensated crystal is flat from -40˚C to 80˚C. If DCF77 synchronization is used then (see below) then problem with quartz accuracy can be ignored.               Hourly Chime Board

Master Clock Display

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