About the MkII
This clock has been designed so that you can take it apart and see how each section works from the power supply up and you can watch the numbers travel through the boards. There are 283 transistors in this clock it uses a crystal oscillator for the main clock
the clock is spread over nine boards and the clock is 14cm high 11cm wide and 9cm deep so it can easily stand on your desk.
the clock is spread over nine boards and the clock is 14cm high 11cm wide and 9cm deep so it can easily stand on your desk.
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Display
The display is controlled from the multiplexer and each segment is flashed >50 times a second so that to the human eye it appear to always be on.
The two hour segments are both flashed at the same time so the frequency to drive all of the segments is 250Hz. 
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Display drivers and diode steering
This board takes the signal from the decoder and turns them into the numbers displayed. There are thirteen drivers on this board which represent zero to twelve from the decoder each driver is connected to a set of steering diodes to display the correct number on the display the drivers also have a zener diode on the input from the decode to stop ghosting on the display and give a clear defined number.
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Decoder 0 - 12
The decoder use npn and pnp transistor to makeup the thirteen logic gates each gate has a led on the output so you can watch the the numbers go through the decoder this was the first part of the clock that I designed.
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Multiplexer
The multiplexer takes the signal from the seconds, minutes and hours boards and combines them all into four bits to go into the decoder each set of bits to go into the multiplexer is clock from the hours / dmc board this board also changes the zero signal from the hours board into twelve and drives the common cathodes on the display segments.
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Hours and multiplexer counter
This board has seven positive edge flip flops four for the hours and three for the display multiplexer counter the display multiplex counter clock is supplied from an astable flip flop running at between 250Hz and 260Hz the counter counts up to five and on the next positive edge resets and the hours counter counts up to nine and on the next positive edge resets.
The hours and the dmc have leds showing the numbers in binary this board also has the button to set the hours when you press the button it disconnects the signal from the minutes board and connects the 2Hz signal from the clock divider board.
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Minutes
This board has seven positive edge flip flops four for the units and three for the tens it also has leds to display the numbers in binary the units count up to nine and on the next positive edge resets and sends a pulse to the minutes tens the minutes tens count up to five and on the next positive edge resets and sends a pulse to the hours board.
This board also has the button to set the minutes when you press the button it disconnects the signal from the seconds board and connects the 2Hz signal from the clock divider board.
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Seconds
This board has seven positive edge flip flops four for the units and three for the tens it also has leds to display the numbers in binary the units count up to nine and on the next positive edge resets and sends a pulse to the seconds tens the seconds tens count up to five and on the next positive edge resets and sends a pulse to the minutes board.
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32.768 KHz divider to 1Hz & 2Hz
This board has fifteen positive edge flip flops to divide the 32.768 KHz from the crystal oscillator down to the 2Hz and 1Hz
clocks the 1Hz is the main clock and the 2Hz is the clock for adjusting the time there are also two leds displaying the 2Hz and 1Hz.
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Power and crystal oscillator
This board has the power supply filtering bridge rectifier and fuse protection on it it also has the main crystal oscillator the main crystal is a standard watch crystal which is 32.768 KHz the wave form from the crystal oscillator goes into a schmitt trigger
which then produces the square wave to go into the clock divider. The clock runs on 5v but the clock without the display on can work down to <3v.
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