[time-nuts] Frequency divider design critique request

Bruce Griffiths bruce.griffiths at xtra.co.nz
Wed Jul 16 17:27:16 EDT 2008

David C. Partridge wrote:
> I'm waiting to see what Magnus Danielson has to say, as it was he after all
> who suggested adding caps in parallel to the pull-downs, and also series
> resistors.
> Thinking about it retrospect, I think he may have meant the series resistors
> to go between the pull-downs and the chip, rather than where the schematic
> fragment showed them.
> I don't *think* switch bounce is an issue here, as it will all settle to the
> right answer pretty sharply.
> Magnus, are you there?
> Cheers
> Dave

Switch bounce could be an issue if one wished to switch cleanly to 
another frequency output without incurring extraneous transitions during 
the changeover from one frequency to another.

A hex D(74HC174) or an octal D(74HC374 74HC574) could be used to 
synchronise debounced multiplexer select inputs.

Another issue is that all BCD switch contacts will not make or break at 
the same time.
Also the debounce filters will not all settle simultaneously.
Thus a debounced enable pushbutton may also be required.
When the enable pushbutton is depressed the current state of the 
selector switches is latched.
In this case only the enable pushbutton need be debounced.


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